Дисертації з теми "Thermal and mechanical stability"

Hard coating 's thermal stability is essential due to the high temperature environment of high-speed cutting applications, while the induced phase and microstructure evolution affects the mechanical properties. In this thesis, the mechanical stability of arc-evaporated hard nitride coatings annealed at high temperature is analyzed and connected to the phase evolution. In addition to hardness, fracture toughness is evaluated by surface and cross-sectional investigations by scanning/transmission electron microscopy of damage events by mechanical tests. The crack resistance of Ti1-xAixN with a range of Al content (x = 0.23-0.82) is studied by contact fatigue tests, where the difference in the microstructure plays a major role. Superior mechanical properties are found in annealed Ti0.63AI0.37N at 900 oC due to the spinodal decomposition. The mechanical and high-temperature properties of hard coatings can be enhanced by alloying or multi-layering. Quaternary Ti-Al-X-N (X = Cr, Nb and V) alloys are studied, and superior toughness is found in TiAI(Nb )N in both the as-deposited and annealed (1100 oC) states. The h-AIN formation in TixAI0.37Cr1-0.37-xN (x = 0.03 and 0.16) is analyzed by in-situ x-ray scattering during annealing. The kinetic energy for h-AIN formation is found to be dependent on the microstructure evolution during annealing, which varies with coating composition. High Al content h-ZrAIN/c-TiN and h-ZrAIN/c-ZrN multilayers are investigated through scratch tests followed by focused ion-beam analysis of the crack propagation. A c-Ti(Zr)N phase forms in h-ZrAIN/c-TiN multilayers at high temperatures and that contributes to enhanced hardness and fracture toughness by keeping the semi-coherency at the sub-interfaces. Finally, an in-situ analysis of coatings by x-ray scattering during a turning process is carried out. lt demonstrates the possibility of observation of stress evolution and thermal expansion of the coatings or the work piece material during machining. This experiment provides real-time information on the coating behavior during cutting.
La estabilidad térmica del recubrimiento es esencial debido a que estos recubrimientos durante su aplicación son utilizados a elevada temperatura y a alta velocidad. Durante dicho proceso, la evolución microestructural afecta a las propiedades mecánicas. En dicha tesis, la estabilidad mecánica de los recubimientos duros base nitruro producidos mediante arco y recocidos a elevada temperatura son analizados y se correlacionado con su transformación de fase. La dureza, la resistencia a la fractura son evaluados mediante la observación tanto superficial como transversal mediante microscopia electrónica de barrido. La resistencia a la propagación de grieta de Ti1−xAlxN con un contenido en Al que fluctúa entre 0.23-0.82 se estudia mediante ensayos de fatiga por contacto, donde la diferencia microstructural juega un papel importante. Las mejores propiedades mecánicas se encentran en las muestras con un 0.63 de Ti donde se ha realizado un proceso de recocido a 900o C debido a la descomposición espinoidal. Las características mecánicas y de alta temperatura de recubrimientos duros pueden ser mejoradas si tenemos un recubrimiento multicapa. Aleaciones cuaternarias de Ti-Al-X-N (X = Cr, Nb y V) son estudiada, y una mejor tenacidad de fractura se encuentra para la muestra TiAl(Nb)N sin tratamiento de recocido como recocida a 1000ºC. La formación del AlN con una estructura hexagonal en la muestra TixAl0.37Cr1−0.37−xN (x = 0.03 y 0.16) son analizadas mediante ensayos in-situ de difracción de rayos X durante el proceso de recocido. Cabe mencionar que la energía cinética para la formación de la AlN con una estructura hexagonal depende del proceso de recocido, la cual hace variar la composición química del recubrimiento. Multicapas de h (hexagonal)-ZrAlN/c (cúbica)-TiN con un elevado contenido de Al son estudiadas mediante ensayos de rayado y la generación de daño es observado mediante la técnica del haz de iones focalizados. Las formas de la fase de c-Ti(Zr)N en las multicapas de (h)-ZrAlN/c-TiN formadas a elevadas temperaturas contribuyen a mejorar la dureza y la tenacidad de fractura manteniendo la semicoherencia en las intercaras entre cada capa. Finalmente, se realiza un análisis in-situ de los diferentes recubrimientos me diante dispersión de rayos X durante un proceso de torneado. En este caso, se demuestra la posibilidad de observar la evolución de las tensiones residuales y de la expansión térmica durante el proceso de conformado. Dicho experimentos proporciona información en tiempo real sobre el comportamiento del recubrimiento en condiciones de servicio.
Hårda skikts högtemperaturstabilitet är viktig på grund av den höga temperaturskikten utsätts för under skärande bearbetning, och den utveckling av faser och mikrostruktur som då sker påverkar skiktets mekaniska egenskaper. I den här avhandlingen har den mekaniska stabiliteten hos arcförångade, hårda metallnitridskikt som värmebehandlats vid höga temperaturer studerats. Förutom hårdhet har även skiktens seghet utvärderats genom yt- och tvärsnittsstudier av den sprickbildning som uppstår vid mekanisk provning med hjälp av svep- och transmissionselektronmikroskopi. Segheten hos Ti1−xAlxN skikt med varierande Al-halt (x = 0.23-0.82) studerades genom utmattningsprovning och resultaten visar att förändringar i mikrostrukturen spelar en stor roll. Ti0.63Al0.37N skikten hade överlägsna mekaniska egenskaper; på grund av en fördelaktig kornstorlek i de obehandlade skikten och efter värmebehandling som ett resultat av det spinodala sönderfall som skett. De mekaniska egenskaperna och högtemperaturegenskaperna hos hårda skikt kan förbättras genom legering eller genom multilagring. I den här avhandlingen har kvarternära Ti-Al-X-N (X = Cr, Nb eller V) skikt studerats och TiAl(Nb)N skikten hade en överlägsen seghet i både obehandlat och värmebehandlat (1100oC) tillstånd. Bildandet av h-AlN i TixAl0.37Cr1−0.37−xN (x = 0.03 and 0.16) skikt studerades genom in situ röntgenspridning under värmebehandling. Den energi som krävs för att bilda h-AlN beror av mikrostrukturutvecklingen under värmebehandling vilken i sin tur beror av skiktens kemiska sammansättning. h-ZrAlN/c-TiN och h-ZrAlN/c-ZrN multilager med hög Al-halt undersöktes genom reptester följda av tvärsnittsstudier av sprickbildningen genom en analys med en fokuserad jonstråle (FIB). En c-Ti(Zr)N fas bildas vid höga temperaturer i h-ZrAlN/c-TiN multilagren och det bidrar till förhöjd hårdhet och förbättrad seghet på grund av en bibehållen koherens mellan lagren. Slutligen har in situ röntgenspridningsstudier av ytskikt utförts vid svarvning. Studien visar på möjligheten att observera spänning och värmeutvidgning av skikten eller arbetsmaterialet under bearbetning. Experimenten ger information om skiktens beteende under bearbetning i realtid.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 97-103).
A fundamental challenge in solar-thermal-electrical energy conversion is the thermal stability of materials and devices at high operational temperatures. This study focuses on the thermal stability of tungsten selective emitters for thermophotovoltaic (TPV) systems which are anticipated to enhance the conversion efficiency. Selective emitters, 2-D photonic crystals, are periodic micro/nano-scale structures that are designed to affect the motion of photons at certain wavelengths. The structured patterns, however, lose their structural integrity at high temperatures, which disrupt the tight tolerances required for spectral control of the thermal emitters. Through analytical studies and experimental observations, the failure modes of tungsten 2-D photonic crystal are indentified. There were four major mechanisms of thermal degradation by which micro/nano-scale structures change their geometry when heated: grain growth and recrystallization, oxidation, surface diffusion, and evaporation. A novel idea of flat surface tungsten photonic crystal (FSTPC) was proposed and was validated by theoretical modeling and by experiments. Pre-annealing or using single crystalline tungsten will prevent the grain growth. A thin layer of diffusion barrier will prevent oxidation and/or evaporation and maintain the optical performance. By filling in the micro/nano-scale cavities with a damascened IR transparent ceramic, the surface of the emitter will have negligible second derivative of the curvature, and thus eliminates the surface diffusion even at high temperatures. Accelerated tests on silicon-based 2-D photonic crystal show that the micro/nano-scale structures on the silicon surface survive for at least 100 hours at 400 °C, homologous temperature of 0.4, which is equivalent temperature of 1200 °C for tungsten. Based on a scale-accelerated failure model, the life time of the Flat Surface Tungsten Photonic Crystal (FSTPC) is estimated to be at least 40 years at 800 °C.
by Heon Ju Lee.
Ph.D.

Polymer composites formed from layered fillers with high surface volume ratio show enhanced reinforcement. Graphite oxide is a high modulus material that can be separated into thin layers with high surface area. The aim of this study is to prepare polymer layered graphite oxide composites using functionalised polyolefin to enhance compatibility with various forms of layered graphite oxide in varying concentration. Functionalised polyolefins reinforced with layered graphite oxides and expanded graphite oxides were prepared using solution blending and melt blending methods. Three different mixing methods with varying shear intensity were employed to prepare polymer layered graphite oxide composites. The crystalline structure, thermal and mechanical properties of the prepared polymer layered graphite oxide composites was studied. Oxidised graphite prepared from the Staudenmaier method and its exfoliated form were dispersed in poly(ethylene-co-methyl acrylate-co-acrylic acid) (EMAA) via solution blending to prepare EMAA layered composites. The thermal stability was determined using thermogravimetric analysis. The EMAA layered composites showed higher thermal stability in comparison with pure EMAA. The mechanical properties of these EMAA layered composites were determined through dynamic mechanical analysis. Shear modulus, yield stress and storage modulus of EMAA in the presence of graphite oxide fillers decreased. A solution blending method was used to prepare poly(propylene-grafted-maleic anhydride) layered expanded graphite oxide composites (PPMA-EGO). Two types of PPMA-EGO were prepared using different mixing methods - low and high shear were employed. The effects of preparative mixing methods on the PPMA-EGO properties were investigated. The mechanical properties of PPMA-EGO obtained from dynamic mechanical analysis indicated that EGO had a reinforcing effect on the elastic behaviour of PPMA-EGO. This is due to strong interfacial adhesion between PPMA and EGO as a result of hydrogen bonding. The elastic behaviour of PPMA-EGO was affected by the surface area of graphite flakes. Low sheared PPMA-EGO elastic behaviour was found to be higher compared with that of high sheared PPMA-EGO. A melt blending method was used to prepare PPMA-EGO with varying EGO concentration. The interconnected network structure of EGO in the PPMA-EGO was not observed as shown by its scanning electron microscopy images. Thermogravimetric analysis of PPMA-EGO indicates increased decomposition temperature of the PPMA matrix. Dynamic mechanical analysis showed enhanced storage modulus of PPMA-EGO. The maximum elastic modulus of PPMA-EGO was observed at 3 %wt of EGO. The electrical conductivity of PPMA-EGO was measured only for EGO concentrations above 2 %wt. The EGO concentration was found to be the most critical factor in the enhancement of the electrical conductivity of PPMA-EGO. Wide angle X-ray diffraction analysis of all polymer layered graphite oxide composites revealed no change in interlayer spacing of graphite layers, indicating the absence of EMAA intercalation in the graphite layers. The crystallisation temperature and crystallinity of all polymer layered graphite oxide composites were determined using differential scanning calorimetry. The results indicated that graphite oxide and expanded graphite oxides acted as nucleating agents in inducing the crystallisation of functionalised polyolefin in the layered composites. However, the degree of crystallinity of functionalised polyolefin decreased in the layered composites.

The large elastic limit, the strength close to the theoretical limit, the excellent magnetic properties and good corrosion resistance of bulk metallic glasses (BMGs) make them promising for several applications such as micro-geared motor parts, pressure sensors, Coriolis flow meters, power inductors and coating materials. The main limitation of these materials is their reduced macroscopic ductility at room temperature, resulting from an inhomogeneous deformation concentrated in narrows shear bands. The poor ductility can be overcome by the incorporation of a ductile second phase in the glassy matrix to form composites, which exhibit a better balance between strength and ductility. Different types of BMG composites have been developed to date but considerable plastic strain during tensile or bending tests has been only obtained for composites with in-situ formation of the second phase during solidification. Among these in-situ formed composites, significant tensile ductility has been only observed for two types of alloys so far: TiZrBe-based and CuZr-based BMG composites. The former precipitate dendrites of the cubic β-(Ti,Zr) phase in the glass matrix, whereas the latter combine spherical precipitates of the cubic B2-CuZr shape memory phase within the glass. The CuZr-based BMG composites have certain advantages over the TiZrBe-based composites such as the absence of Be, which is a toxic element, and exhibit a strong work-hardening behaviour linked to the presence of the shape memory phase. This concept of “shape memory” BMG composites has been only applied to CuZr-based alloys so far. It is worth investigating if such a concept can be also used to enhance the plasticity of other BMGs. Additionally, the correlation between microstructure, phase formation and mechanical properties of these composites is still not fully understood, especially the role of the precipitates regarding shear band multiplication as well as the stress distribution in the glassy matrix, which should be significantly influenced by the precipitates. The aim of the present work is to develop a new family of shape memory bulk metallic glass composites in order to extend the concept initially developed for CuZr-based alloys. Their thermal and mechanical properties shall be correlated with the microstructure and phase formation in order to gain a deeper understanding of the fundamental deformation mechanisms and thermal behaviour. A candidate to form new shape memory BMG composites is the pseudo-binary TiCu-TiNi system because bulk glassy samples with a critical casting thickness of around 1 mm have been obtained in the compositional region where the cubic shape memory phase, B2-TiNi, precipitates. This phase undergoes a martensitic transformation to the orthorhombic B19-TiNi during cooling at around 325 K. The B2- and B19-TiNi exhibit an extensive deformation at room temperature up to 30% during tensile loading. Compositions in the Ti-Cu, Ti-Cu-Ni, Ti-Cu-Ni-Zr, Ti-Cu-Ni-Zr-(Si) and Ti-Cu-Ni-Co systems were selected based on literature data and on a recently proposed λ+Δh1/2 criterion, which considers the effect of atomic size mismatch between the elements and their electronic interaction. Samples were then produced by melt spinning (ribbons) and Cu-mould suction casting (rods and plates). The investigation started in the Ti-Cu system. A low glass-forming ability (GFA) was observed with formation of amorphous phase only in micrometer-thick ribbons and the results showed that the best glass former is located around Ti50Cu50. Considering that the GFA of the binary alloys can be further improved with additions of Ni, new Ti-Cu-Ni shape memory BMG composites were then developed in which the orthorhombic Ti(Ni,Cu) martensite precipitates in the glassy matrix. These alloys exhibit a high yield strength combined with large fracture strain and the precipitates show a reversible martensitic transformation from B19 to B2-type structure at a critical temperature around 320 K (during heating). The amorphous matrix stabilizes the high-temperature phase (B2 phase), which causes different transformation temperatures depending on whether the precipitates are partially or completely embedded in the glassy matrix. The deformation starts in the softer, crystalline phase, which generates a heterogeneous stress distribution in the glassy matrix and causes the formation of multiple shear bands. The precipitates also have the important function to block the fast movement of shear bands and hence retard fracture. However, the size of such composites is limited to 1 mm diameter rods because of their low GFA, which can be further improved by adding CuZr. New Ti-Cu-Ni-Zr composites with diameter ranging from 2 to 3 mm were developed, which consist mainly of spherical precipitates of the cubic B2-(Ti,Zr)(Cu,Ni) and the glassy phase. The interrelation between composite strength and volume fraction of B2 phase was analysed in detail, which follows the rule of mixture for values lower than 30 vol.% or the load-bearing model for higher values. The fracture strain is also affected by the volume fraction of the respective phases with a maximum observed around 30 vol.% of B2 phase, which agrees with the prediction given by the three-body element model. It was observed that the cubic B2 phase undergoes a martensitic transformation during deformation, resulting in a strong work hardening and a high fracture stress of these alloys. The GFA of the Ti-Cu -based alloys can be further increased by minor additions of Si. A maximum GFA is observed for additions of 1 and 0.5 at.% Si to binary Ti-Cu or quaternary Ti-Cu-Ni-Zr alloys, respectively. This optimum GFA results from the formation of a lower amount of highly stable Ti5Si3 precipitates, which act as nuclei for other crystalline phases, and the increased stability of the liquid and the supercooled liquid. The addition of Co has the opposite effect. It drastically decreases the GFA of Ti-Cu-Ni alloys and both the martensitic transformation temperature and their mechanical behaviour seem to correlate with the number and concentration of valence electrons of the B2 phase. The transformation temperature decreases by increasing the concentration of valence electrons. An excellent combination of high yield strength and large fracture strain occurs for Ti-Cu-Ni-Zr and Ti-Cu-Ni-Zr-Si alloys with a relatively low amount of CuZr, with a fracture strain in compression almost two times larger than the one usually observed for CuZr-based composites. For instance, the Ti45Cu39Ni11Zr5 alloy exhibit a yield strength of 1490±50 MPa combined with 23.7±0.5% of plastic strain. However, a reduced ductility was found for the CuZr-richer Ti-Cu-Ni-Zr compositions, which results from the precipitation of the brittle Cu2TiZr phase in the glassy matrix. The present study extends the concept of “shape memory BMG matrix composites” originally developed for CuZr-based alloys and delivers important insights into the correlation between phase formation and mechanical properties of this new family of high-strength TiCu-based alloys, which upon further optimization might be promising candidates for high-performance applications such as flow meters, sensors and micro- and mm-sized gears
Auf Grund der hohen Elastizitätsgrenze, Festigkeiten, die nahe an der theoretischen Grenze liegen, sehr guten magnetischen Eigenschaften, sowie einer guten Korrosionsbeständigkeit erscheint der Einsatz massiver metallischer Gläser (BMG) vielversprechend in zahlreichen Gebieten, wie z.B. in Mikro-Getriebemotorteilen, Coriolis-Massendurchflussmessern, Drucksensoren, Speicherdrosseln und als Beschichtungsmaterialien. Der Einsatz dieser Materialien wird jedoch hauptsächlich durch ihre begrenzte makroskopische Duktilität bei Raumtemperatur eingeschränkt. Diese resultiert aus einer inhomogenen Verformung, die in schmalen Scherbändern konzentriert ist. Die unzureichende Duktilität kann durch das Einbringen einer zweiten, duktilen Phase in die Glas-Matrix verbessert werden, so dass Komposite gebildet werden. Diese Komposite weisen in der Regel immer noch hohe Festigkeiten auf, lassen sich aber gleichzeitig deutlich besser plastisch verformen. Es wurden bereits verschiedene Arten von massiven metallischen Glas-Matrix-Kompositen entwickelt. Jedoch konnte die plastische Verformbarkeit in Zug- oder Biegeversuchen nur in den Materialien erhöht werden, in denen sich die zweite Phase bei der Erstarrung ausscheidet. Unter diesen in-situ Kompositen konnte eine signifikante Duktilität lediglich für zwei Legierungstypen beobachtet werden: massive metallische Gläser auf TiZrBe- und auf CuZr-Basis. Die Ausscheidungen der kubischen β-(Ti,Zr) Phase wachsen dendritenartig in die Glas-Matrix, wohingegen sich in letzterem Legierungstypen sphärische Ausscheidungen der Formgedächtnislegierung, B2-CuZr, im Glas bilden. CuZr-Basislegierungen haben dabei den großen Vorteil, dass sie kein Be enthalten, welches toxisch ist. Außerdem weisen diese Komposite auch dank der Formgedächtnisphase eine starke Kaltverfestigung auf. Das Konzept, massive metallische Formgedächtnis-Glas-Matrix-Komposite herzustellen, um die mechanischen Eigenschaften zu optimieren, wurde bisher nur auf CuZr-Basislegierungen angewandt. Es soll mittels dieser Arbeit nun erforscht werden, ob dieses Konzept auf andere massive metallische Gläser übertragbar ist. Des Weiteren ist der Zusammenhang zwischen Gefüge, Phasenbildung und mechanischen Eigenschaften der Komposite noch nicht vollständig verstanden, insbesondere die Rolle der Ausscheidungen in Bezug auf die Scherbandbildung und die Spannungsverteilung in der Glas-Matrix. Das Ziel der vorliegenden Arbeit ist die Entwicklung einer neuen Klasse massiver, metallischer Formgedächtnis-Glas-Matrix Komposite um das Konzept, welches ursprünglich für CuZr-Basislegierungen entwickelt wurde, zu erweitern. Die thermischen und mechanischen Eigenschaften sollen mit dem Gefüge und der Phasenbildung in Beziehung gesetzt werden, um so die fundamentalen Verformungsmechanismen und ihre Ursachen besser zu verstehen. Der Ausgangspunkt bei der Herstellung neuer massiver metallischer Formgedächtnis-Glas-Matrix Komposite ist das pseudobinäre TiCu-TiNi-System. In diesem System konnten massive Glasproben mit einem kritischen Gießdurchmesser von circa 1 mm hergestellt werden und zwar in dem Zusammensezungsbereich, in dem die kubische Formgedächtnisphase, B2-TiNi, gebildet wird. Während der Abkühlung findet in diesen Kompositen bei etwa 325 K eine martensitische Umwandlung der B2-Phase zur orthorhombischen B19-TiNi Phase statt. B2- und B19-TiNi weisen eine gute Verformbarkeit von bis zu 30% bei Raumtemperatur unter Zugbelastung auf. Die hier erzeugten Ti-Cu, Ti-Cu-Ni, Ti-Cu-Ni-Zr, Ti-Cu-Ni-Zr-(Si) und Ti-Cu-Ni-Co-Legierungen basieren auf Literaturangaben und Vorhersagen bezüglich der Glasbildungsfähigkeit in diesen Systemen mittels λ+Δh1/2-Kriterium, welches die Auswirkungen der Atomgrößenunterschiede der Elemente und deren elektronische Wechselwirkung einbezieht. Die Proben wurden im Schmelzspinnverfahren (Bänder) und mittels Saugguss in einer Cu-Kokille (Stäbe und Bleche) hergestellt. Die Weiter- und Neuentwicklung von Legierungen, beginnt mit dem Ti-Cu-System. Die Glasbildungsfähigkeit in diesem binären System ist nur gering, so dass lediglich mikrometerdicke amorphe Bänder hergestellt werden können. Die Ergebnisse zeigen, dass der beste Glasbildner eine Zusammensetzung von etwa Ti50Cu50 hat. Die Glasbildungsfähigkeit von binären Legierungen kann durch die Zugabe von Ni weiter verbessert werden. Dies führte innerhalb dieser Arbeit zur Entwicklung neuer Ti-Cu-Ni Formgedächtnis-Glas-Matrix Komposite, in welchen die orthorhombische Martensitphase in der Glas-Matrix ausgeschieden wird. Diese ternären Legierungen zeigen eine hohe Zugfestigkeit in Kombination mit einer hohen Bruchdehnung. Beim Überschreiten einer Temperatur von etwa 320 K vollziehen die Ausscheidungen eine reversible martensitische Umwandlung vom B19- zum B2-Strukturtyp. Durch die amorphe Matrix wird die Hochtemperaturphase (B2 Phase) stabilisiert. Dies verursacht unterschiedliche Umwandlungstemperaturen im Kompositmaterial, die davon abhängig sind, ob die Ausscheidungen nur teilweise oder vollständig in der Matrix eingebettet sind. Die Verformung beginnt in der weichen kristallinen Phase, welche eine heterogene Spannungsverteilung in der Glas-Matrix erzeugt und eine hohe Dichte an Scherbändern in der Matrix verursacht. Die Ausscheidungen haben zudem die Funktion, die Ausbreitung der Scherbänder zu blockieren und das Versagen des Materials zu verzögern. Die Größe der Komposite ist jedoch auf Grund der geringen Glasbildungsfähigkeit auf einen Stabdurchmesser von ca. 1 mm begrenzt. Dies kann mit dem Zulegieren von CuZr verbessert werden. Es wurden hier auf diese Weise neue Ti-Cu-Ni-Zr Komposite entwickelt, deren Durchmesser zwischen 2 und 3 mm liegt. Diese bestehen hauptsächlich aus sphärischen Ausscheidungen der kubischen B2-(Ti,Zr)(Cu,Ni)- und der Glasphase. Die wechselseitige Beziehung zwischen der Streckgrenze und dem Volumenanteil der B2-Phase wurde im Detail untersucht. Für kristalline Volumenanteile kleiner als 30 Vol.-% folgt die Streckgrenze der Mischungsregel und für größere Volumenanteile dem „lasttragenden Modell“ (load bearing model). Die Bruchdehnung wird ebenfalls vom Volumenanteil der Phasen beeinflusst und zeigt ein Maximum bei etwa 30 Vol.-% an B2-Phase. Dies stimmt mit der Vorhersage des „Drei-Element-Modells“ überein. Es wurde festgestellt dass die kubische B2-Phase während der Verformung eine martensitische Umwandlung durchführt, was die starke Kaltverfestigung und die hohen Bruchspannungen dieser Legierungen zur Folge hat. Die Glasbildungsfähigkeit von TiCu-Basislegierungen kann im Gegenzug weiterhin durch geringe Si-Zusätze gesteigert werden. Hierbei tritt jeweils ein Maximum bei Zusätzen von 1 und 0,5 at-% Si zu binären Ti-Cu- oder zu quarternären Ti-Cu-Ni-Zr-Legierung auf. Das Optimum der Glasbildungsfähigkeit ist das Ergebnis sowohl eines geringeren Anteils hochschmelzender Ti5Si3-Ausscheidungen, die als Keimbildner für andere kristalline Phasen dienen, als auch der erhöhten Stabilität der Schmelze sowie der unterkühlten Schmelze. Der Zusatz von Co wiederum hat einen gegenteiligen Effekt. Er vermindert die Glasbildungsfähigkeit von Ti-Cu-Ni-Legierungen drastisch. Zudem scheinen sowohl die martensitische Umwandlungstemperatur als auch das mechanische Verhalten mit der Zahl und Konzentration der Valenzelektronen der B2-Phase zu korrelieren. Die Umwandlungstemperatur sinkt mit steigender Valenzelektronenkonzentration. Eine ausgezeichnete Kombination von hoher Streckgrenze und Bruchdehnung tritt für die Legierungen Ti-Cu-Ni-Zr und Ti-Cu-Ni-Zr-Si mit einem relativ geringen CuZr-Anteil auf. Die Bruchdehnung unter Druck ist fast zweimal höher als es für CuZr-Basis-Komposite gewöhnlich beobachtet worden ist. Die Legierung Ti45Cu39Ni11Zr5 zeigt beispielsweise eine Streckgrenze von 1490±50 MPa in Kombination mit einer plastischen Dehnung von 23,7±0,5%. Für die CuZr-reicheren Ti-Cu-Ni-Zr Zusammensetzungen wurde jedoch eine geringere Duktilität festgestellt, was das Resultat spröder Cu2TiZr-Ausscheidungen in der Glas-Matrix ist. Die vorliegende Arbeit erweitert folglich das Konzept der „Formgedächtnis-Glas-Matrix Komposite“, welches bisher auf CuZr-basierte Legierungen beschränkt war und liefert wichtige Einblicke in die Beziehung zwischen Phasenbildung und mechanischen Eigenschaften der neuen Klasse hochfester TiCu-Basislegierungen, welche nach weiterer Optimierung vielversprechend sein könnten für Hochleistungsanwendungen wie Durchflussmesser, Sensoren und mikrometer- und mm-große Antriebe

Polymeric materials have a wide variety of applications in many manufacturing industries. However, because of the molecular structures and chemical compositions of polymeric materials, they have considerably low resistances against fire or heat. Although these materials are highly flammable, their flame retardancy can be improved significantly by incorporating the flame retardant nanomaterials. Nanoclay, nanotalc and graphene are some of the examples of the flame retardant nanomaterials. These are highly cost effective and environmentally friendly for these applications. These inclusions have a great potential to improve thermal, electrical, and mechanical properties of the new materials. This study is mainly focused on the effects of nanoparticle additions in the polyvinyl chloride (PVC) in terms of the flame retardancy. Five sets of nanocomposite materials were prepared using the solvent casting method at different weight percentages of the nanomaterials. The flame retardancy values of the resultant nanocomposite samples were determined using the ASTM UL 94 standard tests. The results of the experiment were also supported by the thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Surface characterization of the resultant materials was carried out using scanning electron microscopy (SEM), while mechanical properties were determined through a tensile test method. Test results showed that the flame retardancy values of the new nanostructured materials were significantly enhanced in the presence of nanoscale inclusions, which may be useful for various industrial applications. This study may open up new possibilities of using many nanoscale inclusions in various polymers as flame retardant materials for different industrial applications.
Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Mechanical Engineering

In this study, Al-Al2O3 nanocomposite powders containing 5, 10 and 15 Wt% of nanopowder were produced by mechanical alloying. For comparing, Al-Al2O3 composite powder containing 5Wt% of micrometric Al2O3 was also produced. The powder was then hot-pressed in a mold to produce bulked parts. The effect of Al2O3 content on grain growth, density, hardness and bending strength of bulked composite was discussed and microstructures were investigated by optical, scanning and transmission electron microscopy. The results revealed that when nanometric particles were used instead of micrometric particles the grain growth was reduced, while the increase of particle weight percentage did not affect the grain growth. The results also showed that when weight percentage of nanometric particles was increased, although hardness of bulked parts was increased but relative density and bending strength was reduced severely. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/34932

Equal Channel Angular Pressing (ECAP) is one of the methods which allows to obtain ultrafine-grained and nanocrystalline metallic materials. It is well known that microstructure of materials pro-cessed by ECAP in not very stable. There were published many experimental and theoretical evidences of this fact obtained by various methods such as microstructure observations, properties measurement and computer modeling. The aim of presented paper was to investigate the thermal stability of microstructure and mechanical properties of the Al 5483 alloy processed by ECAP. As a result of performed investigations it was concluded that accumulated plastic deformation has no influence on the thermal stability of Al 5483 alloy processed by ECAP. It was also found that properly chosen parameters of ECAP and subsequent annealing allows to produce materials with high strength and plasticity. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35435

La synthèse par métallurgie des poudres de nickel à grains ultrafins (UFG) a été effectuée, et l’effet de l’affinement de la microstructure sur le comportement mécanique et les propriétés physiques a été étudié. La possibilité de coupler le broyage et le frittage flash est étudiée avec des résultats prometteurs. Des échantillons de haute densité avec des tailles de grains d = 0.65 – 4 µm, caractérisés par une fraction élevée des joints de grains Σ3 et un faible niveau de contrainte ont été synthétisés. Les propriétés mécaniques des échantillons UFG montrent une bonne combinaison ductilité-résistance mécanique, avec un impact mineur des porosités présentes. L’étude de l’influence de la taille de grain dans le régime UFG sur les propriétés mécaniques montre une limite d’élasticité supérieure à celle attendue et une capacité d’écrouissage plus faible. Ces observations sont cohérentes avec la microstructure déformée à rupture, étudiée par diffraction d’électrons rétrodiffusés et microscopie électronique en transmission. Une haute diffusivité, mesurée par des expériences de traceurs radioactifs, montrent des profils de pénétration très différents liés aux structures de porosités diverses présents dans les échantillons. Ces différentes structures sont aussi responsables de la densification rétrograde observée, uniquement pour les échantillons frittés à partir de poudres broyées
The present manuscript concerns the synthesis of ultrafine grained (UFG) Ni by powder metallurgy, and the study of the influence of UFG microstructures on the mechanical behavior and physical properties. The possibilities of coupling ball milling and Spark Plasma Sintering are presented showing promising results. Highly dense homogeneous specimens are obtained, with average grain sizes d = 0.65 - 4 µm, and microstructures highlighted by a high fraction of Σ3 grain boundaries dependent on grain size. The mechanical properties in tensile testing for UFG samples are evaluated showing a good combination of strength and ductility, with little impact from porosities, the major drawback of powder metallurgy. The influence of grain size in the UFG regime on the mechanical properties is investigated, showing strength values that deviate from the expected behavior for grain refinement. Likewise, a reduced strain hardening capacity is depicted which correlates to the microstructural observations performed on the deformed state. High diffusivity measured by means of radiotracer experiments is observed in the sintered samples, displaying different penetration profiles that relate to diverse porosity structures. Such structures are also responsible for retrograde sintering observed exclusively in samples processed from BM powders

The geological disposal of nuclear waste, in underground openings and the long-term performance of these openings demand a detailed understanding of fundamental rock mechanics. A full scale field experiment: Äspö Pillar Stability Experiment was conducted at a depth of 450 m in sparsely fractured granitic rock to examine the rock mass response between two deposition holes. An oval shaped tunnel was excavated parallel to the σ3 direction to provide access to the experiment and also provide elevated stress magnitudes in the floor. In the tunnel floor two 1.75-m diameter 6-m deep boreholes were excavated so that a 1-m thick pillar was created between them. In one of the holes a confinement pressure of 700 kPa was applied and in the other displacement transducers were installed. The pillar volume was monitored by an Acoustic Emission System. Spatially distributed thermocouples were used to monitor the temperature development as the pillar was heated by electrical heaters. The excavation-induced stress together with the thermal-induced stress was sufficient to cause the wall of the open borehole to yield. The temperature-induced stress was increased slowly to enable detailed studies of the rock mass yielding process. Once the rock mass loading response was observed, the rock mass was unloaded using a de-stress slotting technique. This thesis focuses on the in-situ study of the rock mass response to coupled mechanical thermal loading and thermal-mechanical unloading. The experiment, its design, monitoring and observations are thoroughly described. An estimate of the yielding strength of the rock mass is presented and compared with laboratory test and results from other rock mass conditions reported elsewhere in the open literature. General conclusions about the effect of the confining pressure and the observations from the unloading of the pillar are also presented. Important findings are that the yielding strength of the rock mass has been successfully determined, low confinement pressures significantly affects the onset of yielding, the primary mode of fracture initiation and propagation is extensional, no significant time dependency of the yielding process was observed. The unloading studies also indicated that what appeared to be shear bands likely was a propagating zone of extensile failure that weakened the rock so that displacements in the shear direction could occur.

QC 20100622

This Thesis demonstrates an experimental study on the development of thermoset-based natural fiber particle-reinforced composite. The overall objective was to improve the mechanical properties and investigate the thermal stability of the composite. It addresses, the effect of various chemical treatment of filler types, filler size, filler percentage and matrix type on the mechanical properties and thermal stability of the composite. To improve the mechanical performance, a hybrid composite containing carbon nanotubes was also synthesized.

This licentiate thesis reports experimental and theoretical work on the high temperature mechanical properties and the thermal stability of cubic (c)-(Ti-Cr-Al)1-N1 coatings. It is demonstrated that it is possible to tailor and improve the properties of hard nitride coatings by different degrees of multicomponent alloying. When Cr is added to Ti-Al-N the coatings exhibit age hardening up to 1000 ºC which is higher compared to what is observed for Ti-Al-N. In addition, the coatings show a less pronounced hardness decrease when hexagonal (h)-Al-N is formed compared to Ti-Al-N. The improved thermal stability is discussed in terms of a lowered coherency stress and a lowered enthalpy of mixing due to the addition of Cr. When Ti is added to Cr-Al-N the formation and growth of the detrimental h-Al-N phase is suppressed and delayed improving the mechanical properties. This is discussed in terms of kinetic effects where the Ti atoms obstruct the Al diffusion and consequently the growth of h-Al-N precipitates. The microstructure evolution investigated at different stages of spinodal decomposition, coarsening and phase transformations are correlated to the thermal responses and the mechanical hardness of the coatings. Upon annealing up to 1400 ºC the coatings decompose into c-TiN, bcc-Cr and h-AlN. The decomposition takes place via several intermediate phases, c-CrAlN, c-TiCrN and hexagonal (β)-Cr2N.    The oxidation resistance of (Tix-Cry-Al60)1-N1 is also investigated and presented for different x/y ratios. The results show that it is possible to generate coatings with both excellent mechanical properties and oxidation resistance improving the functionality in the working temperature range of 850-1100 ºC of for example cutting tools.

COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
Neste trabalho são apresentados os efeitos nas propriedades mecânicas, estruturais e tribológicas da incorporação de flúor em filmes de carbono amorfo hidrogenados depositados por Deposição na Fase Vapor Assistido por Plasma . A estabilidade térmica de filmes de carbono amorfo fluorados também foi estudada. Os filmes foram depositados a partir de uma mistura dos gases C2H2 e CF4 com uma tensão de autopolarização de - 350V. A mistura de gases da deposição foi variada de uma concentração de 0% até 90% de CF4. A estabilidade térmica foi verificada em filmes depositados com 50% de C2H2 e 50% de CF4 na atmosfera precursora. Os filmes foram submetidos a temperaturas variando de 200oC a 600oC por 30 minutos. As propriedades mecânicas, estruturais e tribológicas dos filmes foram estudados com o uso de técnicas nucleares (retroespalhamento de Rutherford e Detecção por recuo elástico), espectroscopia Raman, espectroscopia de fotoelétrons induzida por raios-X, perfilometria (tensão interna), nanoindentação (dureza), de microscopia de força atômica e de ângulo de contato. Os resultados obtidos mostraram que a incorporação de flúor produzem filmes com as propriedades indo em direção às propriedades do Teflon. Os filmes ricos em flúor são menos densos, mais macios, mais hidrofóbicos e tem um menor coeficiente de atrito do que filmes de carbono amorfo hidrogenados. O tratamento térmico realizado mostrou que os filmes são estáveis a temperaturas de até 300oC. A partir desta temperatura os filmes sofreram perda de flúor e mudanças nas suas propriedades indicando a formação de uma estrutura mais grafítica.
This work presents the effects on the mechanical, structural and tribological properties of the incorporation of fluorine in amorphous carbon films deposited by PECVD (Plasma Enhanced Chemical Vapor Deposition). The thermal stability of fluorinated amorphous carbon films was also studied. The films were deposited using mixtures of C2H2 and CF4 gases with a self-bias voltage of - 350V. The concentration of CF4 in the gases mixture was varied from 0% to 90%. The thermal stability was investigated in films deposited with 50% C2H2 and 50% CF4 as precursor atmosphere. These films were annealed in the temperatures range of 200oC to 600oC during 30 minutes for each sample. The mechanical, structural and tribological properties were studied using nuclear techniques (Rutherford Backscattering and Elastic Recoil Detection Analysis), Raman and X-ray photoelectron spectroscopy, profilometry (for internal stress) and nanoidentation (for hardness), atomic force microscopy and contact angle measurements. The results showed that fluorine incorporation produces films with properties resembling the Teflon's properties. The films rich in fluorine appear to have lower density, more hydrophobicity and lower friction coeficient than amorphous carbon films. They are also softer than them. The thermal annealing shows that films were thermally stable within temperatures up to 300oC. Above this temperature the films tend to loose fluorine and their properties change revealing a more graphitic structure.

Thesis (MScEng)--Stellenbosch University, 2013.
ENGLISH ABSTRACT: An accurate description of the atmospheric boundary layer (ABL) is a prerequisite for computational fluid dynamic (CFD) wind studies. This includes taking into account the thermal stability of the atmosphere, which can be stable, neutral or unstable, depending on the nature of the surface fluxes of momentum and heat. The diurnal variation between stable and unstable conditions in the Namib Desert interdune was measured and quantified using the wind velocity and temperature profiles that describe the thermally stratified atmosphere, as derived by Monin- Obukhov similarity theory. The implementation of this thermally stratified atmosphere into CFD has been examined in this study by using Reynoldsaveraged Navier-Stokes (RANS) turbulence models. The maintenance of the temperature, velocity and turbulence profiles along an extensive computational domain length was required, while simultaneously allowing for full variation in pressure and density through the ideal gas law. This included the implementation of zero heat transfer from the surface, through the boundary layer, under neutral conditions so that the adiabatic lapse rate could be sustained. Buoyancy effects were included by adding weight to the fluid, leading to the emergence of the hydrostatic pressure field and the resultant density changes expected in the real atmosphere. The CFD model was validated against measured data, from literature, for the flow over a cosine hill in a wind tunnel. The standard k-ε and SST k-ω turbulence models, modified for gravity effects, represented the data most accurately. The flow over an idealised transverse dune immersed in the thermally stratified ABL was also investigated. It was found that the flow recovery was enhanced and re-attachment occurred earlier in unstable conditions, while flow recovery and re-attachment took longer in stable conditions. It was also found that flow acceleration over the crest of the dune was greater under unstable conditions. The effect of the dune on the flow higher up in the atmosphere was also felt at much higher distances for unstable conditions, through enhanced vertical velocities. Under stable conditions, vertical velocities were reduced, and the influence on the flow higher up in the atmosphere was much less than for unstable or neutral conditions. This showed that the assumption of neutral conditions could lead to an incomplete picture of the flow conditions that influence any particular case of interest.
AFRIKAANSE OPSOMMING: 'n Akkurate beskrywing van die atmosferiese grenslaag (ABL) is 'n voorvereiste vir wind studies met berekenings-vloeimeganika (CFD). Dit sluit in die inagneming van die termiese stabiliteit van die atmosfeer, wat stabiel, neutraal of onstabiel kan wees, afhangende van die aard van die oppervlak vloed van momentum en warmte. Die daaglikse variasie tussen stabiele en onstabiele toestande in die Namib Woestyn interduin is gemeet en gekwantifiseer deur gebruik te maak van die wind snelheid en temperatuur profiele wat die termies gestratifiseerde atmosfeer, soos afgelei deur Monin-Obukhov teorie, beskryf. Die implementering van hierdie termies gestratifiseerde atmosfeer in CFD is in hierdie studie aangespreek deur gebruik te maak van RANS turbulensie modelle. Die handhawing van die temperatuur, snelheid en turbulensie profiele in die lengte van 'n uitgebreide berekenings domein is nodig, en terselfdertyd moet toegelaat word vir volledige variasie in die druk en digtheid, deur die ideale gaswet. Dit sluit in die implementering van zero hitte-oordrag vanaf die grond onder neutrale toestande sodat die adiabatiese vervaltempo volgehou kan word. Drykrag effekte is ingesluit deur die toevoeging van gewig na die vloeistof, wat lei tot die ontwikkeling van die hidrostatiese druk veld, en die gevolglike digtheid veranderinge, wat in die werklike atmosfeer verwag word. Die CFD-model is gevalideer teen gemete data, vanaf die literatuur, vir die vloei oor 'n kosinus heuwel in 'n windtonnel. Die standaard k-ε en SST k-ω turbulensie modelle, met veranderinge vir swaartekrag effekte, het die data mees akkuraat voorgestel. Die vloei oor 'n geïdealiseerde transversale duin gedompel in die termies gestratifiseerde ABL is ook ondersoek. Daar is bevind dat die vloei herstel is versterk en terug-aanhegging het vroeër plaasgevind in onstabiele toestande, terwyl vloei herstel en terug-aanhegging langer gevat het in stabiele toestande. Daar is ook bevind dat vloei versnelling oor die kruin van die duin groter was onder onstabiele toestande. Die effek van die duin op die vloei hoër op in die atmosfeer is ook op hoër afstande onder onstabiele toestande gevoel, deur middel van verhoogte vertikale snelhede. Onder stabiele toestande, is vertikale snelhede verminder, en die invloed op die vloei hoër op in die atmosfeer was veel minder as vir onstabiel of neutrale toestande. Dit het getoon dat die aanname van neutrale toestande kan lei tot 'n onvolledige beeld van die vloei toestande wat 'n invloed op 'n bepaalde geval kan hê.

The effects of octadecylamine-functionalized reduced graphene oxide (FRGO) on the frictional and wear properties of diglycidylether of bisphenol-A (DGEBA) epoxy are studied using a pin-on-disk tribometer. It was observed that the addition of FRGO significantly improves the tribological, mechanical, and thermal properties of epoxy matrix. Graphene oxide (GO) was functionalized with octadecylamine (ODA), and then reduction of oxygen-containing functional groups was carried out using hydrazine monohydrate. The Raman and x-ray photoelectron spectroscopy studies confirm significant reduction in oxygen-containing functional groups and formation of ODA functionalized reduced GO. The nanocomposites are prepared by adding 0.1, 0.2, 0.5 and 1.0 wt % of FRGO to the epoxy. The addition of FRGO increases by more than an order of magnitude the sliding distance during which the dynamic friction is ≤ 0.1. After this distance, the friction sharply increases to the range of 0.4 - 0.5. We explain the increase in sliding distance during which the friction is low by formation of a transfer film from the nanocomposite to the counterface. The wear rates in the low and high friction regimes are approximately 1.5 x 10-4 mm3/N·m and 5.5 x 10-4 mm3/N·m, respectively. The nanocomposites exhibit a 74 % increase in Young’s modulus with 0.5 wt. % of FRGO, and an increase in glass transition and thermal degradation temperatures.

Mechanical property and thermal stability of Zr-Si-N films of varying silicon contents deposited on Al₂O₃ (0001) substrates are characterized. All films provided for characterization were deposited by reactive DC magnetron sputter deposition technique from elemental Zr and Si targets in a N₂/Ar plasma at 800 ^oC. The hardness and microstructures of the as deposited films and post-annealed films up to 1100 ^oC are evaluated by means of nanoindentation, X-ray diffractometry and transmission electron microscopy. The Zr-Si-N films with 9.4 at.% Si exhibit hardness as high as 34 GPa and a strong (002) texture within which vertically elongated ZrN crystallites are embedded in a Si₃N₄ matrix. The hardness of these two dimensional nanocomposite films remains stable up to 1000 ^oC annealing temperatures which is in contrast to ZrN films where hardness degradation occurs already above 800 ^oC. The enhanced thermal stability is attributed to the presence of Si₃N₄ grain boundaries which act as efficient barriers to hinder the oxygen diffusion. X-ray amorphous or nanocrystalline structures are observed in Zr-Si-N films with silicon contents > 13.4 at.%. After the annealing treatments, crystalline phases such as ZrSi₂, ZrO₂ and Zr₂O are formed above 1000 ^oC in the Si-containing films while only zirconia crystallites are observed at 800 ^oC in pure ZrN films because oxygen acts as artifacts in the vacuum furnace. The structural, compositional and hardness comparison of as-deposited and annealed films reveal that the addition of silicon enhances the thermal stability compared to pure ZrN films and the hardness degradation stems from the formation of oxides at elevated temperatures.

Recent experimental advances for the fabrication of various borophene sheets introduced new structures with a wide range of applications. Borophene is the boron atom analogue of graphene. Borophene exhibits various structural polymorphs all of which are metallic. In this work, we employed first-principles density functional theory calculations to investigate the mechanical properties of five different single-layer borophene sheets. In particular, we analyzed the effect of the loading direction and point vacancy on the mechanical response of borophene. Moreover, we compared the thermal stabilities of the considered borophene systems. Based on the results of our modelling, borophene films depending on the atomic configurations and the loading direction can yield a remarkable elastic modulus in the range of 163–382 GPa nm and a high ultimate tensile strength from 13.5 GPa nm to around 22.8 GPa nm at the corresponding strain from 0.1 to 0.21. Our study reveals the remarkable mechanical characteristics of borophene films.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, June 2011.
"June 2011." Cataloged from PDF version of thesis.
Includes bibliographical references (p. 51-52).
As the world's traditional energy sources come under scrutiny due to dwindling supply and negative environmental impact, a global effort is being made into alternative energy systems. One such system involves the use of thermophotovoltaics (TPV), which convert thermal energy to electricity. Nano-patterned features can im prove electromagnetic emission from the TPV emitter, increasing system efficiency. These features, however, degrade at high temperatures over tine. One of the main contributors to surface evolution is surface diffusion. This investigation tested surface diffusion based simulation modeling, comparing computational results with experimental findings for high temperature annealed silicon, a cost effective material for testing instead of tungsten. Although the simulation model fits within 25% of the post-annealed curvature caused by surface diffusion, discrepancies in the simulation's time scale need to be addressed in future models for accurate time dependent modeling.
by Sun K. Kim.
S.B.

Thesis submitted in fulfillment of the requirements for the degree Doctor of Technology: Mechanical Engineering Cape Peninsula University of Technology, 2013
Fluid flow through a porous channel and cylindrical pipe walls are important area of research due to its wide applications in transpiration cooling, gaseous diffusion technology, cooling of rocket, mechanized irrigation and filtration processes. It is therefore necessary to examine the effect of Navier slip, combined effects of buoyancy forces and variable viscosity on the entire flow structure. Analyzing the magneto- hydrodynamics (MHD) of unsteady flow with buoyancy effect and also investigate numerically the entropy generation in an unsteady flow through porous pipe. We have also examined the thermal stability and entropy generation in the system. The problems were investigated theoretically using appropriate mathematical models for both transient and steady state scenario. Both analytical techniques and numerical methods are employed to tackle the model nonlinear equations derived from the law of conservation of mass, momentum and energy balance. Some definitions of terms to come across and introduction to fluid flow are given in chapter 1, together with literature reviews, statement of problem and objectives of the study. Chapter 2 lays the foundation for basic fundamental equations governing fluid flow. In chapter 3, the combined effect of suction/injection and asymmetric Navier slip on the entropy generation rate for steady flow of an incompressible viscous fluid through a porous channel subjected to different temperature at the walls are investigated. Chapter 4 analyze combined effects of buoyancy forces together with Navier slip on the entropy generation in a vertical porous channel wall with suction/injection wall. Analysis of MHD unsteady flow through a porous pipe with buoyancy effects are carried out in chapter 5, while chapter 6 investigates numerically entropy generation of unsteady flow through a porous pipe with suction and chapter 7 gives concluding remarks.

Equal channel angular pressing ECAP is a process whereby simple shear is applied to a billet during multiple passages through an angled channel of constant cross section. The process is capable of generating very large plastic strains that significantly refines the microstructure without altering the external dimensions of the billet. A number of properties are influenced by grain refinement with the generation of a submicron grain structure SMG by ECAP resulting in improved strength and hardness and enhanced superplasticity. In this thesis, both an AA7075 alloy and AA7075 Al-base metal matrix composite MMC reinforced with 5 wt. percent of 50 nm diameter SiC particles was produced by a powder metallurgy route followed by hot extrusion. The materials were subsequently deformed by ECAP at 350 C to a true effective strain of 4.6 in an attempt to refine the microstructure and further distribute the SiC reinforcement phase in the composite. The high temperature microstructural stability of both the as-deformed alloy and composite was investigated to elucidate the effect of the reinforcement phase on continuous and discontinuous grain coarsening. It was found that ECAP generated a fine equiaxed grain size of ~ 2.3 !m and ~1.8 !m in the alloy and composite, respectively. The composite was more refined after ECAP since the SiC particles allow the matrix to undergo more grain refinement during deformation. ECAP was found to be a reasonable method for further distributing SiC clusters in this composite which is important for optimizing the reinforcement phase in terms of ambient temperature strengthening and enhanced grain stability at elevated temperature. Both the alloy and composite were annealed at times up to 5h at 500 C to assess grain stability. During annealing, the grain structure of both materials evolved in a continuous manner unlike the discontinuous process of recrystallization. Such a process is similar to continuous recrystallization observed in a range of heavily deformed Al alloys. Substantial grain boundary interactions with MgZn2 precipitates and oxide particles were found in the alloy, with precipitate, oxide and SiC particles found in the composite. The strong pinning force exerted by these particles minimised grain growth in both materials with the composite exhibiting a finer less than 2.5 !m grain size than the alloy less than 3.5 !m after extended annealing. This enhanced grain stability was attributed to the high volume fraction SiC particles which resulted in a large value of the dispersion parameter f/d which results in significant boundary pinning during annealing. Grain stability was also analysed in terms of a recently-proposed mean field model of annealing where it was predicted that the composite should not undergo discontinuous coarsening, as observed experimentally.

In this thesis, the effect of mechanical deformation on structure, thermal stability and hardness of a single-phase spray-deposited quasicrystalline alloy with composition Al62.5Cu25Fe12.5 has been investigated in detail. The purpose of the investigation was to study the effect of mechanical milling at different milling speeds (which approximately scale with the milling intensity) on mechanically-induced phase transformations during milling and on the phase evolution during subsequent heating. The results of the milling experiments indicate that, irrespective of the milling speeds used, mechanical milling of Al62.5Cu25Fe12.5 quasicrystals leads to the formation of a disordered CsCl-type ß phase with grain size of about 10 – 20 nm. The analysis of the kinetics of the QC–to–ß phase transformation reveals that the milling intensity has a considerable effect on the characteristics of the transformation. The increase of the milling speed considerably shortens the incubation time needed to start the QC–to–ß phase transformation. Also, the overall transformation is much faster for milling at high speeds. The QC–to–ß phase transformation starts when the grain size of the quasicrystals is reduced to about 10 nm irrespective of the milling speed used and clearly indicates that a critical grain size of the quasicrystals for initiating the transformation exists. On the other hand, no critical value of lattice strain was found for the QC–to–ß transformation. This indicates that the phase transformation is controlled by the local length scale (i.e. the grain size) and by the corresponding grain boundaries rather than by the energy stored in the lattice. Energetic considerations obtained through a simple model based on the mass and velocity of the milling balls reveal that the energy needed for the QC–to–ß transformation increases with increasing the milling speed, that is, the energetic efficiency of the process decreases with increasing the milling intensity. This indicates that part the extra energy supplied during milling at high intensities is not used to induce the phase transformation but it is dissipated by heat. During heating, the milled powder displays a multi-step thermal behavior characterized by the grain growth of the disordered ß phase at low temperatures, followed, at higher temperatures, by its transformation into the original icosahedral quasicrystalline phase. The transformation is gradual and the quasicrystals and the disordered ß phase coexist over a temperature interval of more than 250 K. The phase transformations occurring during milling and subsequent annealing have a remarkable effect on the hardness, which can be tuned within a wide range of values (7–9.6 GPa) as a function of the volume fraction of the different phases. This suggests that a composite material with optimized mechanical properties can be produced by an appropriate thermo-mechanical treatment. The quasicrystals milled at a very low speed show a transition between Hall-Petch to inverse Hall-Petch behavior at a grain size of about 40 nm, which represents the critical value for grain size softening of the present Al62.5Cu25Fe12.5 quasicrystals. This behavior may be attributed to the complexity of the quasicrystalline structure and to its peculiar deformation mechanism at room temperature (i.e. shear banding), where meta-dislocation-assisted deformation is almost absent. In order to analyze the effectiveness of the Al62.5Cu25Fe12.5 quasicrystals as reinforcing agent in metal matrix composites, Al-based composites were synthesized by hot extrusion of elemental Al blended with different amounts of Al62.5Cu25Fe12.5 quasicrystalline particles. The work was focused on two specific aspects: evaluation of the mechanical properties through room temperature compression tests and modeling of the resulting properties. The addition of the quasicrystalline reinforcement is very effective for improving the room temperature mechanical properties of pure Al. The compressive strength increases from 155 MPa for pure Al to 330 and 407 MPa for the composites with 20 and 40 vol.% of reinforcement, respectively, reaching an ultimate strain of 55 % and 20 % before fracture occurs. These results indicate that the addition of the QC reinforcement leads to composite materials with compressive strengths exceeding that of pure Al by a factor of 2 – 2.5, while retaining appreciable plastic deformation. The mechanical properties of the composites have been modeled by taking into account the combined effect of load bearing, dislocation strengthening and matrix ligament size effects. The calculations are in very good agreement with the experimental results and reveal that the reduction of the matrix ligament size, which results in a similar strengthening effect as that observed for grain refinement, is the main strengthening mechanism in the current composites. Finally, the interfacial reaction between the Al matrix and the QC reinforcement has been used to further enhance the strength of the composites through the formation of a new microstructure consisting of the Al matrix reinforced with Al7Cu2Fe w-phase particles. The optimization of the structure-property relationship was done through the systematic variation of the processing temperature during consolidation. The mechanical behavior of these transformation-strengthened composites is remarkably improved compared to the parent material. The yield strength of the composites significantly increases as the Al + QC -> ω transformation progresses from 195 MPa for the sample reinforced only with QC particles to 400 MPa for the material where the Al + QC -> ω reaction is complete. These results clearly demonstrate that powder metallurgy, i.e. powder synthesis by ball milling followed by consolidation into bulk specimens, is an attractive processing route for the production of novel and innovative lightweight composites characterized by high strength combined with considerable plastic deformation. In addition, these findings indicate that the mechanical behavior of Al-based composites reinforced with Al62.5Cu25Fe12.5 quasicrystalline particles can be tuned within a wide range of strength and plasticity depending on the volume fraction of the reinforcement as well as on the extent of the interfacial reaction between Al matrix and QC reinforcing particles.

The GMT-Consortium Large Earth Finder (G-CLEF) is an echelle spectrograph with precision radial velocity (PRV) capability that will be a first light instrument for the Giant Magellan Telescope (GMT). G-CLEF has a PRV precision goal of 40 cm/sec (10 cm/s for multiple measurements) to enable detection of Earth-like exoplanets in the habitable zones of sun-like stars'. This precision is a primary driver of G-CLEF's structural design. Extreme stability is necessary to minimize image motions at the CCD detectors. Minute changes in temperature, pressure, and acceleration environments cause structural deformations, inducing image motions which degrade PRV precision. The instrument's structural design will ensure that the PRV goal is achieved under the environments G-CLEF will be subjected to as installed on the GMT azimuth platform, including: Millikelvin (0.001 K) thermal soaks and gradients 10 millibar changes in ambient pressure Changes in acceleration due to instrument tip/tilt and telescope slewing Carbon fiber/cyanate composite was selected for the optical bench structure in order to meet performance goals. Low coefficient of thermal expansion (C 1E) and high stiffness-to-weight are key features of the composite optical bench design. Manufacturability and serviceability of the instrument are also drivers of the design. In this paper, we discuss analyses leading to technical choices made to minimize G-CLEF's sensitivity to changing environments. Finite element analysis (FEA) and image motion sensitivity studies were conducted to determine PRV performance under operational environments. We discuss the design of the optical bench structure to optimize stiffness to -weight and minimize deformations due to inertial and pressure effects. We also discuss quasi-kinematic mounting of optical elements and assemblies, and optimization of these to ensure minimal image motion under thermal, pressure, and inertial loads expected during PRV observations.

Combined thermionic emission and tunneling of hot electrons (thermo-tunneling) has emerged as a potential new solid state cooling technology. Practical implementation of thermotunneling, however, requires the formation of a nanometer-sized gap spanning macroscopically significant surfaces. Thermotunneling is a term used to describe combined emission of hot electrons (thermionic emission) and tunneling of electrons through a narrow potential barrier between two surfaces (field emission). Thermo-tunneling of hot electrons across a few nanometer gap has application to vacuum electronics, at panel displays, and holds great potential in thermo-electric cooling and energy generation. Development of new thermo-tunneling applications requires creation of a stable nanometer gap between two surfaces. Formation of such a small scale gap is very challenging. Due to the various type of the forces that come to the picture in the scale of nanometer gap creates a complex interaction between the engaged surfaces. In this project different setups of a test device is suggested to form a nanometer-sized gap appropriate for tunneling current generation. Having a mathematical model describing the physical characteristics of such a system is inevitable in order to examine the stability of the system's dynamics. The first set of externally applied forces selected to stabilize the system is composed of electrostatic force that attracts two surfaces opposed by an electro-magnetic force. The electro-magnetic force is produced by applying an external magnetic field to in the proximity of the thin flexible electrode which carries electrical current due to the electron tunneling. The orientation of the external magnetic field is set to generate a force in the opposite direction of the electrostatic force. The second setup of the experimental model is composed of electrostatic force opposed by the thermoelastic force. The thermoelastic force is generated due to the thermal expansion/contraction of the flexible beam. The configuration of the designed device determines the direction of which the thermoelastic force is applied. This project is focused on our effort to investigate the stability of the thin flexible micro structure under mentioned opposing forces and feasibility study of the fabrication of such a device.

This thesis deals with complex analysis of fine-grained magnesium alloy AZ91 prepared by ECAP process. Mechanical properties of investigated alloy in different states at various external conditions are compared. The structure of this material is inherently unstable therefore changes on microstructural and sub-microstructural level occur during thermal exposure and/or mechanical loading. These changes are analysed and quantified for investigated alloy in selected states in this thesis.

Cette étude porte sur l’apport de nouvelles fonctionnalités à des matériaux élastomères qui seront utilisés pour la réalisation de gants. Des additifs possédant des propriétés antimicrobiennes ainsi que des charges possédant des propriétés radioprotectrices sont insérées dans des matrices polymères. La méthode de mise en œuvre utilisée est l’enduction par trempage, l’impact de ces additifs sur les propriétés rhéologiques de solutions dans lesquelles les élastomères sont dissous sont analysées. L’incorporation de certaines amines peut entraîner une vulcanisation des élastomères en solution. Après la réalisation d’échantillons par trempage, la stabilité thermique des élastomères est étudiée par analyse thermogravimétrique ainsi que par une analyse infrarouge. Certains oxydes métalliques peuvent modifier la dégradation thermique d’élastomères comportant des groupes chlorés en favorisant la déchlorination. L’impact des additifs sur les élastomères vulcanisés a également été étudié, ces mesures ont permis de mettre en évidence l’impact de certains additifs sur la vulcanisation ainsi que les interactions charges-élastomère par la mise en évidence de l’effet Mullins. Enfin, une méthode de détermination des propriétés radioprotectrices des élastomères a été mise en place afin de déterminer les formulations fournissant la meilleure atténuation aux rayonnements ionisants
The aim of this study is to give new functionalities to elastomers that will be used as gloves. Some antimicrobials and radioprotective additives will be incorporated in different polymer matrixes. The elastomers have been realized by dip coating, the impact of the additives on the rheological properties of the solutions of elastomers was analysed. Some amines can interact with the elastomers in the solvent and accelerate the vulcanization. The thermal stability of the charged elastomers has then been investigated by thermogravimetric analysis and infrared measurments. Some metallic oxides interact with elastomers containing chlorine and change the dehydrochlorination process. The impact of the additives on the mechanical properties of vulcanized elastomers has been studied, the impact of some additives on the vulcanization and the existence of strong charge-polymer interactions have been demonstrated. Finally, a method to measure the radioprotective properties of filled elastomers has been developed to measure the attenuation of the composite against ionizing radiations

This thesis is a study of the heat transfer correlations between a wire and liquid helium cooled to either 1.9 or 4.3 K. The wire resembles a part of a superconducting magnet used in the Large Hadron Collider (LHC) particle accelerator currently being built at CERN. The magnets are cooled to 1.9 K and using helium as a coolant is very efficient, especially at extremely low temperatures since it then becomes a superfluid with an apparent infinite thermal conductivity. The cooling of the magnet is very important, since the superconducting wires need to be thermally stable.

Thermal stability means that a superconductive magnet can remain superconducting, even if a part of the magnet becomes normal conductive due to a temperature increase. This means that if heat is generated in a wire, it must be transferred to the helium by some sort of heat transfer mechanism, or along the wire or to the neighbouring wires by conduction. Since the magnets need to be superconductive for the operation of the particle accelerator, it is crucial to keep the wires cold. Therefore, it is necessary to understand the heat transfer mechanisms from the wires to the liquid helium.

The scope of this thesis was to describe the heat transfer mechanisms from a heater immersed in liquid and superfluid helium. By performing both experiments and simulations, it was possible to determine properties like heat transfer correlations, critical heat flux limits, and the differences between transient and steady-state heat flow. The measured values were in good agreement with values found in literature with a few exceptions. These differences could be due to measurement errors. A numerical program was written in Matlab and it was able to simulate the experimental temperature and heat flux response with good accuracy for a given heat generation.

The present study was aimed at exploring the purification and modification of montmorillonite rich Turkish bentonites by organic salts and their subsequent effects on the morphology (X-diffractometry, transmission electron microscopy, scanning electron microscopy), melt flow index, mechanical (Tensile, Impact) and especially thermal stability (thermal gravimetric analysis, differential scanning calorimetry) properties of polymer/organoclay nanocomposites with and without an elastomeric compatibilizer. The bentonite clay mined from Resadiye (Tokat/Turkey) was purified by sedimentation, resulting in higher cation exchange capacity and thermal stability in comparison to unpurified clay, and then used in the synthesis of six thermally stable organoclays by replacing the interlayer inorganic sodium cations with two (alkyl, aryl) phosphonium and four di-(alkyl, aryl) imidazolium surfactant cations in an attempt to overcome the problem of early decomposition of alkyl ammonium organoclays usually used in polymer nanocomposites. An optimum amount of these organoclays (wt %2) was then used in the production of Polyamide 66 and Poly(ethylene terephthalate) based nanocomposites by melt blending with the help of an optimum amount of elastomeric compatibilizer (wt %5) which also acted as impact modifier. Phosphonium organoclays were used in the production of nanocomposites for both polymers, whereas imidazolium organoclays were used with PET only. The importance of clay purification was revealed in the removal of non-clay minerals available in the raw bentonite clay as confirmed by XRF and XRD, the significant increase in cation exchange capacity and the improved thermal stability of the purified clays as proven by TGA. The interlayer spacing of the phosphonium organoclays ranged from 1.78 to 2.52 nm indicating arrangement between pseudo-trilayers and paraffin-type chains, while the interlayer spacing of imidazolium organoclays ranged between 1.35 nm and 1.45 nm indicating a monolayer arrangement. The effects of chemical structure (chain type), counter ion and alkyl chain length on the thermal stability of the imidazolium salts were investigated. TGA analysis showed that the thermal stability of (alkyl, aryl) phosphonium and di-(alkyl, aryl) imidazolium organoclays proved to be superior to conventionally used quaternary alkyl ammonium organoclays. Not only the thermal stability of the organoclays prevented the nanocomposite from early decomposition, but these organoclays also improved the onset decomposition temperatures of PA66 and PET nanocomposites compared to the pure polymer owing to the dominant barrier effect of the silicate layers as a result of the formation of carbonaceous-silicate char. The reinforcement of PA66 with surface modified phosphonium organoclays and PET with surface modified phosphonium and imidazolium organoclays enhanced the mechanical and thermal properties of the binary and ternary nanocomposites. The mechanical properties were in good agreement with DSC analysis for all the PA66 and PET compositions. The presence of elastomer and organoclays promoted the nucleation process in PA66 blend, binary and ternary nanocomposites. However, the presence of elastomer and organoclay retarded the nucleation in most of the PET composites.

Fundamental thermodynamic investigations have been carried out regarding the phase equilibria of La0.8Sr0.2MnO3±δ (LSM), a cathode of a solid oxide fuel cell (SOFC), utilizing the CALculation of PHAse Diagram (CALPHAD) approach. The assessed thermodynamic databases developed for LSM perovskite in contact with YSZ fluorite and the other species have been discussed. The application of computational thermodynamics to the cathode is comprehensively explained in detail, including the defect chemistry analysis as well as the quantitative Brouwer diagrams, electronic conductivity, cathode/electrolyte interface stability, thermomechanical properties of the cathode and the impact of gas impurities, such as CO2 as well as humidity, on the phase stability of the cathode. The quantitative Brouwer diagrams for LSM at different temperatures are developed and the detailed analysis of the Mn3+ charge disproportionation behavior and the electronic conductivity in the temperature range of 1000-1200°C revealed a good agreement with the available experimental observations. The effects of temperature, CO2 partial pressure, O2 partial pressure, humidity level and the cathode composition on the formation of secondary phases have been investigated and correlated with the available experimental results found in the literature. It has been indicated that the CO2 exposure does not change the electronic/ionic carriers’ concentration in the perovskite phase. The observed electrical conductivity drop is predicted to occur due to the formation of secondary phases such as LaZr2O7, SrZrO3, SrCO3 and Mn oxides at the LSM/YSZ interface, resulting in the blocking of the electron/ion transfer paths. For the thermo-mechanical properties of LSM, a new weight loss Mechanism for (La0.8Sr0.2)0.98MnO3±δ using the La-Sr-Mn-O thermodynamic database is modeled with respect to the compound energy formalism model. This newly proposed mechanism comprehensively explains the defect formation as a result of volume/weight change during the thermal cycles. According to the proposed mechanism the impact of cation vacancies regarding the volume change of cathode was explained.

Au cours de cette étude, nous nous sommes intéressés à l’influence de l’acide (sa force, sa structure, sa taille, sa nature, etc. ) et de l’ajout d’eau sur les caractéristiques des CLIPs. Nous avons pu démontrer que la stabilité thermique dépend fortement de la basicité et de la nature de l’anion (Td > 300°C). Les conductivités sont plutôt influencées par la structure et la taille de l’anion, les meilleures conductivités étant obtenues pour des anions de super acide de petite taille. Pour ce qui est des membranes, celles à base de Nafion® ont démontré une très bonne conduction protonique mais une tenue mécanique insuffisante. Les membranes denses à base de polysulfone ont des propriétés très insuffisantes tant du point de vue mécanique que de la conduction. Les dernières membranes étudiées à base de polymères macropreux de type polyimide ont montré les meilleures performances dans tous les domaines étudiés et semblent les mieux adaptées pour l’application PEMFC « Haute température »
The purpose of this thesis was to study the effect of the starting acid (strength, structure, size, type…) and of the water concentration on the CLIP’s properties. We showed that thermal stability was controlled by the anion’s basicity and its nature (Td > 300°C). On the other hand, conductivity has been found dependent on the size and the type of the anion (best conductivities for small sized super acid anion). Membranes are based on the association of a CLIP with a polymer (Nafion®, sulfonate polysulfone, polyimide). Nafion® based membranes showed good conductivities but poor mechanical properties at high temperature. Sulfonated polysulfone based membranes have both low toughness and low conductivities. The last studied electrolyte, based on macroporous polyimide, exhibited the highest conductivities and the best thermomechanical properties; they seem to be the most adapted membranes for the PEMFC application

La technologie de pulvérisation magnétron par impulsions de haute puissance (HiPIMS) a été développée et est considérée comme une méthode efficace pour la préparation des films. La technologie HiPIMS permet une bien plus grande flexibilité pour ajuster la structure et les performances du film, conduisant à des films avec des propriétés uniques qui sont souvent irréalisables dans les autres approches PVD. Cependant, le mécanisme sous-jacent du plasma pour soutenir la croissance du film impliqué est actuellement flou. De plus, la technologie HiPIMS est limitée au laboratoire, de nombreux films aux propriétés souhaitables n'ont pas été explorés dans le cadre de la pulvérisation HiPIMS. Dans ce travail, (i) le l’origine de la structure cohérente du plasma haute densité (les « spokes ») dans la décharge HiPIMS et (ii) comment la structure et les propriétés des films de TaC/a-C:H et HfC/a-C:H sont gérées par HiPIMS ont été étudiés. Dans l'étude du mécanisme de formation des « spokes », basée sur la relation de dispersion du plasma HiPIMS et l'évolution du couplage entre deux ondes azimutales, un modèle d'onde induit par couplage a été proposé. Dans l'étude des films TaC/a-C:H et HfC/a-C:H, les états des liaisons chimiques, la structure, la morphologie, les propriétés mécaniques et tribologiques, la stabilité thermique ainsi que la résistance à l'oxydation des films ont été étudiés. En comparaison avec ces films déposés par pulvérisation magnétron DC, il est démontré que la technologie HiPIMS permet une stratégie potentielle pour préparer des films TaC/a-C:H et HfC/a-C:H plus performants en termes de dureté, de coefficient de frottement et de résistance à l'usure, de résistance à l'oxydation et de stabilité thermique en modulant l'état de liaison chimique et la structure nanocomposite des films à travers un plasma réactif
High Power Impulse Magnetron Sputtering technology (HiPIMS) has been developed and considered as an effective method for film preparation. HiPIMS technology allows for much greater flexibility for manipulating film structure and performance, leading to films with unique properties that are often unachievable in the other PVD approaches. However, the underlying plasma mechanism for supporting film growth is currently blurred. Moreover, HiPIMS technology is still stationed in the laboratory, many films with desirable properties have not been explored under HiPIMS framework. In this work, (i) the driven mechanism of high density plasma coherent structure (i.e., spokes) in the HiPIMS discharge and (ii) how the structure and properties of the TaC/a-C:H and HfC/a-C:H films are regulated by HiPIMS were investigated. For the driven mechanism of spokes, based on the dispersion relationship of HiPIMS plasma and the evolution of the coupling between two azimuthal waves, the coupling-induced wave model was proposed. For the TaC/a-C:H and HfC/a-C:H films, the chemical bond states, structure, morphology, mechanical and tribological properties, thermal stability as well as oxidation resistance of the films were investigated. By comparison with DC deposited films, it is demonstrated that HiPIMS technology provides a potential strategy for preparing higher performance TaC/a-C:H and HfC/a-C:H films in terms of hardness, friction coefficient and wear resistance, oxidation resistance and thermal stability by modulating the chemical bonding state and nanocomposite structure of the films through HiPIMS reactive plasma

The glassy wormlike chain model is a highly successful phenomenological model recently introduced to describe anomalously slow subdiffusive dynamics in biopolymer networks and living cells. Here we extend this model by proposing a generic scheme how to include nonlinear plastic effects by introducing the possibility of force-dependent opening and closing of internal bonds. Further, we discuss physiological implications of this bond kinetics. Stability arguments lead us to the postulation of a “physiological sheet” in the parameter space. This sheet defines the set of parameters characterizing cells which are flexible enough to perform biological tasks while still being able to bear external perturbations characteristic of their surroundings and their internally generated prestress without damage. At the end of this contribution, we speculate about the connection between prestress and cell stiffness and about the mechanism by which the cell adapts to its mechanical environment.

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The three cylinder motors tend to vibrate more than the conventional four cylinder ones. In this new condition the transmission system and in particular the torsional damper of the clutch disc is subjected to sever wear and friction. The great challenge is to select new materials with low wear rate and adequate friction coefficient to attenuate this new vibration level. In this work three different candidate materials to be used as friction rings inside the torsional damper of clutch discs were tested in terms of wear resistance and friction. Two of the studied materials are currently used in the market (PA66 35 GF and NBR) in four cylinder motors and the third is currently used in clutch facing (NBR matrix composite). The materials were purchased from Schaeffler suppliers. The first step was the microstructural characterization and determination of the thermal stability of the three materials without the influence of friction. For that, the microstructure was analyzed by optical and electronic microscopy of Scanning (SEM), the amount of fibers and inorganic reinforcers was determined by burning tests and,the transition temperatures were determined by differential calorimetry. Two aging temperatures were studied 80 and 150oC. The effect of the ageing time was determined by hardness and infrared spectroscopy measurements. Among the three materials and clutch facing, they show a more stable structure in the temperature range between 80 and 150ºC. The PA66GF35 suffered changes in crystalline content and the NBR thermal degradation. The second step consisted in determining the wear characteristics of the material in bench tests with the objective of measuring the wear rate and friction coefficient of the material under extreme conditions of specific pressure and velocity (DIN50320, 1979). The results of the friction test had the following classification: NBR (0.13)> PA66GF35 (0.11)> clutch facing (0.09). Despite having a lower coefficient of friction, the clutch facing was the only material that achieved the minimum wear resistance required for the friction ring. Therefore the clutch facing is the best material for a 3 cylinder engine that requires a higher wear and thermal resistance on the clutch plate.
O motor de três cilindros tende a ter vibrações maiores que do motor de quatro cilindros. Nesta nova configuração o sistema de transmissão e, em particular, o amortecedor torcional do disco de embreagem fica sujeito a condições de desgaste e atrito mais severas. O grande desafio atual está na busca de componentes com baixo desgaste e um coeficiente de atrito adequado e que elimine os ruídos. Neste trabalho foram caracterizados os materiais utilizados na fabricação de anéis de atrito do amortecedor torcional de discos de embreagem quanto à resistência ao desgaste e atrito. Dois dos três materiais são hoje utilizados no mercado como componente de anel de atrito (PA66GF35 e elastômero NBR) em motores de quatro cilindros e o terceiro é atualmente utilizado em Lonas de embreagem. A primeira etapa consistiu na caracterização microestrutural e determinação da estabilidade térmica dos três materiais sem a influência de atrito. Para isso foram realizadas análises em microscopia óptica e eletrônica de varredura (MEV), teste de queima para porcentagem de fibra e tratamentos de envelhecimento, seguido de análises através de calorimetria diferencial, dureza, espectroscopia no infravermelho. Dentre os três materiais a lona de embreagem mostrou ser a mais estável na faixa de temperaturas entre 80 e 150ºC. O PA66GF35 sofreu alteração de cristalinidade e o NBR endurecimento devido à degradação térmica. A segunda consistiu na determinação das características de desgaste do material em função das variáveis de influência em condições controladas de laboratório. Para isso foi realizado um teste de bancada com o objetivo de medir a taxa de desgaste e coeficiente de atrito do material em condições extremas de pressão específica e velocidade (DIN50320, 1979). Os resultados do ensaio o atrito teve a seguinte classificação: NBR (0,13) >PA66GF35 (0,11)>Lona (0,09). Apesar de ter um coeficiente de atrito menor, a Lona de embreagem foi o único material que atingiu a resistência ao desgaste mínima exigida para o anel de atrito. Portanto a Lona de embreagem é o melhor material para um motor 3 cilindros que exige uma maior resistência ao desgaste e térmica, no disco de embreagem.

Etude des proprietes mecaniques, de la stabilite thermique de la diffusion de l'eau et de sels radioactifs dans des polyurethannes. Les polyetherurethannes souples ont un comportement moyen a la temperature et a la diffusion. Les polyesterurethannes ont un meilleur comportement mais sont hydrolyses rapidement les polyetherurethannes rigides (tv=20 a 40#oc) sont le meilleur compromis; amelioration de la tenue en temperature vers 350-500#oc par addition de derives furanniques

Les alliages de cuivre sont utilisés dans de nombreuses applications électriques car ils offrent un bon compromis de résistance mécanique, de résistance à la corrosion et de conductivité électrique. Cependant pour certaines applications comme les contacteurs électriques, des matériaux plus performants sont recherchés. L’affinement de la taille de grains et l’implantation ionique sont deux voies que nous avons explorées dans ce but. Afin d’obtenir un bon compromis entre la dureté, la résistance à la corrosion et la conductivité électrique du cuivre pur (99,90%) et un bronze commercial monophasé contenant 8 % massique d’étain ont été nanostructurés par déformation plastique intense, et ensuite implantés à l’azote. Dans un premier temps, nous avons étudié l’évolution de la dureté des matériaux que nous avons corrélée aux changements microstructuraux induits par déformation plastique intense. Grâce à la microscopie électronique en transmission (MET) et la diffraction des rayons X (DRX), nous avons pu mettre en évidence la formation de grains ultrafins. Et nous avons prouvé que la solution solide CuSn métastable n’était pas décomposée au cours de la déformation. Par ailleurs, il a été montré que l’étain en solution solide favorise l’affinement des grains et que la déformation du CuSn8 à des vitesses plus rapides limite la restauration dynamique des défauts en engendrant une plus grande dureté. Un modèle qualitatif prenant en compte la production et l’annihilation de dislocations a été développé permettant de prédire l’influence des paramètres procès sur l’évolution de la microstructure et de la dureté. La stabilité thermique des nanostructures formées par déformation intense a également été étudiée, notamment par calorimétrie différentielle à balayage. Il a été montré que l’ajout d’étain en solution solide retarde la recristallisation alors que la densité de défauts et donc la force motrice est plus importante. Le Cu et le CuSn8 recristallisés et à grains ultrafins ont été implantés à l’azote. Il a été montré par nanoindentation que les duretés superficielles du Cu recristallisé et du Cu nanostructuré augmentent significativement après implantation. Nous avons mis en évidence par MET (SAED, STEM HAADF et EELS) la formation de nitrures de cuivre qui sont à l’origine du durcissement superficiel. Des nitrures de cuivre ont été également été formés dans le CuSn8 alors qu’aucun nitrure d’étain n’a été détecté. Par ailleurs, il est intéressant de noter que les défauts et notamment les mâcles formées après déformation intense semblent favoriser la diffusion de l’azote et être des sites de germination préférentielle des nitrures de cuivre
Copper is the most used material in electrical field applications. For electrical contacts, its oxidation behavior, thermal stability and hardness is essential. In this work, we attempted to find the key to make strong, but also conductive metal with a high corrosion resistance by finding an appropriate copper microstructure and surface treatment. It is well known that material properties are determined by their microstructure. Also, it was seen that nitride films enhance the oxidation resistance and the surface hardness. Therefore, to achieve our goal, pure copper and a bronze alloy Cu-8wt. %Sn have been subjected to high pressure torsion to make ultra-fine-grains and the surface was then implanted with nitrogen ions. We have investigated the effect of deformation on the hardness and the thermal stability by Vickers microhardness and DSC measurements. It is shown that tin in solid solution delay the recrystallization of the UFG produced by HPT. Tin also promotes the grain refinement and limit the dynamic annihilation during HPT deformation. Furthermore, a correlation between the properties and the microstructure was done by SEM and TEM analyses. A qualitative model taking into account the production and annihilation of dislocations has been developed to predict the influence of process parameters on the evolution of microstructure and hardness. Recrystallized and UFG Cu and CuSn8 were implanted with nitrogen. It has been shown by nanoindentation that their surface hardness increase significantly after implantation. TEM analyses (SAED, STEM HAADF and EELS) demonstrated the formation of copper nitrides which cause superficial hardening. Copper nitrides were also formed in CuSn8 whereas no tin nitride was detected. Moreover, it is interesting to note that the defects (in particular deformation twins) seem to be preferential nucleation sites for copper nitrides

This investigation was done at NTNU and together with Statoil research and development department in Rotvoll, Trondheim to facilitate a new semi dynamic amine thermal degradation rig.This study was an initial attempt to investigate semi dynamic thermal stability rig as an alternative to thermal degradation study. The major purposes are: (1) to study MEA and MDEA thermal degradation by thermal stability rig apparatus which is designed by Statoil. (2) to demonstrate the result differences between the new and conventional experimental method. MEA and MDEA were selected in this study due to have more available literature data in amine based absorption process. The loaded liquid was circulated through the pipe from the cold stream to the hot stream. There is no analytical method was connected to the rig therefore a regular sample was taken every week and sent to SINTEF analytical lab to identify degradation products.Residence time of solution in high temperature zone also was calculated as an important factor in thermal degradation investigation. Different authors have been provided to understand: the background, the experimental set up, the analytical method to describe the degradation products, data interpretation and the mechanism of the degradation.Based on analytical results, it seems that only small portion of MEA and MDEA were degraded. It showed that the elapsed time was not enough to observe degradation in a significant amount. Metal qualification tests showed low metal concentration in solutions and generally very little corrosiveness effect. However, few degradation products were reported in this study the most probably degradation mechanism is estimated similar to suggested degradation pathway by Davis (2009). More works are required in future to better interpret the new thermal stability rig.

The objective of this research was to quantitatively describe the the denaturation and aggregation processes of a-lactalbumin at neutral pH in order to understand their interrelationship and effect on solution stability. Three different preparations of a-La had similar denaturation temperatures, enthalpies and % reversibility as measured by differential scanning calorimetry. However, Native PAGE reveled three non-native monomer bands that corresponded to three distinct dimer bands indicating specific intramolecular disulfide bond shuffling leads to formation of disulfide-specific dimers. The apo protein was the most thermostable to turbidity development. The Ca-La was the most thermostable holo- preparation. Turbidity development at 95 degreesC (95 degrees C) indicated pure preparations intensely associate through hydrophobic interactions through bridging by divalent phosphate and this effect was mitigated by decreasing the ionic strength, decreasing the phosphate charge to ¡V1 (at pH 6.6) or decreasing the temperature. The aggregation behavior of a commercial a-La was investigated at neutral pH and 95?aC in a complex mineral salt environment to understand general stability factors involved in a nutritional beverage. The objective was to understand the effect of a-La lot variation, relative b-lactoglobulin concentration and excess calcium on the aggregate size development as measured by light scattering and turbidity development. The lot of holo-a-La possessing a higher intrinsic b-Lg concentration had higher solubility at pH 6.80, evolved more reactive thiol groups, had a 25% faster first order rate constant, dissociated only slightly with cooling and formed spherical aggregates with a much higher molecular weight. Aggregates intrinsic to the protein powder may play a role in aggregate growth and shape. Adding increasing quantities of b-Lg generally decreased solubility. The highest b-Lg concentrations investigated demonstrated a net thiol oxidation and, subsequently, had a diminished ability to aggregate through hydrophobic interactions. Adding excess calcium caused a dramatic loss of solubility at pH 7.0 and required an increase in pH to 7.5 to regain solubility.