Tesis sobre el tema "High Niobium"
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Lyne, Michael Peter. "High resolution spectroscopy of aminoborane and niobium nitride". Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/26442.
Texto completoScience, Faculty of
Chemistry, Department of
Graduate
Huang, Gejian. "High resolution spectroscopy of niobium nitride and vanadium oxide". Thesis, University of British Columbia, 1988. http://hdl.handle.net/2429/27961.
Texto completoScience, Faculty of
Chemistry, Department of
Graduate
Cain, Victoria. "High temperature creep behaviour niobium bearing ferritic stainless steels". Thesis, Cape Peninsula University of Technology, 2005. http://hdl.handle.net/20.500.11838/1249.
Texto completoThe objective of this project was to monitor the high temperature creep behaviour of 441 stainless steel. Two different alloys of 441 were investigated; the main difference between them being the Niobium content. Particularly imporlant to the project was how the Niobium content and grain size affected the creep resistance of the material. Creep tests were performed using purpose built constant load creep test rigs. Initially the rigs were not suitable for the testing procedures pertaining to this project. This was due to persistent problems being experienced with regards the reliability and reproducibility of the rigs. After various modifications were made the results produced from the rigs were consistent. Creep test data was used in order to determine the mechanism of creep that is operative within the material (at a predetermined temperature) under a predetermined load. Particular attention was paid to the resulting stress exponents. in order to identify the operative creep mechanism. The identification of the operative creep mechanisms was also aided by microscopical analysis. This analysis was also necessary to monitor how the grain size had altered at various annealing temperatures. Heat treatment was used as a method to alter the high temperature strength and microstructure of the material. Heat treatments were performed at various temperatures in order to determine the ideal temperature to promote optimum creep resistance of 441. All heat treatments were performed in a purpose designed and built high temperature salt bath furnace. The commissioning of the salt bath formed part of the objectives for this project. Sag testing was also conducted, using purpose built sag test rigs. It was necessary to design and manufacture a sag test rig that could be comparable to the industry accepted method of sag testing known as the two-point beam method, as this method is believed to produce inconsistent results. Conclusions have been drawn from the results of the data and from previous research on the subject matter.
Wynn, C. L. "Vanadium and niobium high strength low alloy steels for light gauge high strength strip". Thesis, Swansea University, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636700.
Texto completoKakarlapudi, Purushotham Raju. "High temperature oxidation response of Nb-20W-10Cr alloy in air". To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2008. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.
Texto completoGOMEZ, LUIS BELTRAN. "HIGH FREQUENCY ELECTRICAL TRANSPORT MEASUREMENTS OF NIOBIUM SNS JOSEPHSON JUNCTION ARRAYS AND NIOBIUM THIN FILMS WITH NANOSCALE SIZE MAGNETIC DOT ARRAY". University of Cincinnati / OhioLINK, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1054743123.
Texto completoVentura, Julieta Angelica. "High temperature oxidation behavior of Nb-20Mo-15Si-5B-20Cr alloy". To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2009. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.
Texto completoDicks, Robert Paul. "The development of niobium-silicide based materials for high temperature applications". Thesis, University of Birmingham, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.521943.
Texto completoMignanelli, Paul Michael. "The design of new nickel-base superalloys with high niobium contents". Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709110.
Texto completoPortillo, Benedict I. "High temperature oxidation behavior of the Nb-W-Cr system and response of boron additions". To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2008. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.
Texto completoSucci, Giovanni. "Analysis of impregnated Niobium-Tin coils for the High-luminosity LHC magnets". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/17800/.
Texto completoMoricca, Maria del Pilar. "High temperature oxidation characteristics of Nb-10W-XCr alloys". To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2009. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.
Texto completoDevillet, F., J. M. Geets, M. Ghyoot, E. Kral, R. Mooij, B. Nactergal y M. Vosjan. "High power conical-shaped Niobium targets for reliable [18F-] production and lower [18O] water consumption". Helmholtz-Zentrum Dresden - Rossendorf, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-164985.
Texto completoCallender, Chad M. "Refractory metal to nickel-based alloy joining technologies for high temperature applications". Auburn, Ala., 2006. http://repo.lib.auburn.edu/2006%20Summer/Theses/CALLENDER_CHAD_35.pdf.
Texto completoWang, Jing. "Electrodeposition and characterisation of nickel-niobium-based diffusion barrier metallisations for high temperature electronics interconnections". Thesis, Loughborough University, 2016. https://dspace.lboro.ac.uk/2134/20590.
Texto completoBuck, Terry J. "Muon spin rotation characterization of superconducting niobium for applications in high field superconducting radio frequency cavities". Thesis, University of British Columbia, 2016. http://hdl.handle.net/2429/57093.
Texto completoScience, Faculty of
Physics and Astronomy, Department of
Graduate
Duncan, Julia Carmel. "The effect of nitrogen, niobium and temperature of the high temperature oxidation of titanium aluminide alloys". Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/49663.
Texto completoIncludes bibliographical references (leaves 237-247).
This is especially attractive for reducing the engine weight and increasing the thrust/weight ratio. Increasing the operating temperature and thereby the engine efficiency has approached the maximum possible operating temperature for currently used materials. A model set of three intermetallics -- unalloyed [gamma]-TiAl, unalloyed [alpha]-Ti 3Al and a nearly stoichiometric Ti2NbAl (an orthorhombic intermetallic structure) -- was chosen and investigated under a variety of experimental conditions. Gas mixtures of varying oxygen concentrations in both argon and nitrogen allowed the effect of oxygen concentration on oxidation kinetics to be investigated. The Ti 2NbAl-alloy was specifically chosen to examine the effect of Nb in a intermetallic compound (with Nb substituting for one Ti in the Ti 3Al intermetallic structure). This is in contrast to Nb as a simple alloy addition to y-TiAl or c 2-Ti 3Al. Exposures at temperatures of 700°C and 800°C for 20 and 100 hours were studied (compared to temperatures of 900°C or higher used by other investigators), since these temperatures promoted a more protective scale. Additionally, the scale composition is sensitive to temperature and restricts the conventional practice of corrosion study acceleration by raising the experimental temperature. The resulting corrosion scales were analyzed using electron microscopy (scanning and transmission), x-ray diffraction and thermogravimetric analysis. The effect of nitrogen in the gaseous environment was explored. The impact of Nb on the oxidation of the intermetallics was found to be more protective than what might be expected from examining the thermodynamics and kinetics of the Ti-Al-Nb-O-N system. At times an alternating layered scale structure resulted and the effect of N, Nb and the lower temperatures used in this study is summarized. The oxidation rate of the Ti 2NbAl-alloy fell between the rates for y-TiAl and c 2-Ti 3Al, with the scale on y-TiAl growing at the slowest rate of the three compositions. However, the superior mechanical properties of Ti2 NbAl-alloy combined with the acceptable corrosion resistance promote its consideration for replacing those portions of the engine operating at intermediate temperatures that would result in significant weight and cost savings.
by Julia Carmel Duncan.
Sc.D.
Wang, Tong. "Enhanced Field Emission Studies on Nioboim Surfaces Relevant to High Field Superconducting Radio-Frequency Devices". Diss., Virginia Tech, 2002. http://hdl.handle.net/10919/29284.
Texto completoPh. D.
Jacquemin, Manoël. "Structure et propriétés supraconductrices de films de nitrure de niobium épitaxiés par CVD à haute température". Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAI054/document.
Texto completoThe studies concern the development of superconducting devices for single photon detection. Niobium nitride (NbN) is a material suitable for the production of superconducting wires for the detector target. This work is opening up perspectives on the development of epitaxial niobium nitride films on sapphire by the chemical vapor deposition (CVD) method. The production of thin films (5-100 nm) is carried out at high temperature (1000°C to 1300°C) from niobium chloride and ammonia diluted in hydrogen (H2-NH3-NbCl5). The substrate is oriented single crystalline sapphire (Al2O3) (0002), aluminum nitride (AlN) (0002) or magnesium oxide (MgO) (100).The study of epitaxial relationships during the growth of niobium nitride on the sapphire substrate was first performed. Observation of the microstructures and crystalline orientations of the various films processed made it possible to highlight the relationships between the surface state of the substrate and the growth mode of NbN. The potential for using single crystal substrates such as MgO and AlN is discussed in the conclusion.The study of the growth process and the relationships between the working conditions and the "quality" of thin films made it possible to identify the experimental windows leading to epitaxial growth. The activation energy of the growth reactions and the supersaturation conditions favorable to epitaxial growth were calculated.The study of the interactions between the structural properties and superconducting properties of films has allowed the superconducting transition temperature to be linked to the density of atomic defects, microstructural defects, the thickness of the films and their stress state. There is a linear relationship between the interplanar space of planes parallel to the substrate and the superconducting transition temperature.Finally, the durability of ultra-thin films (5 - 8 nm) of niobium nitride was studied. The electrical and superconducting properties of films processed at 1000°C and 1200°C on sapphire substrates and epitaxial layers of AlN were analyzed over a period of six months. The properties of films change most notably during the first month. High temperature deposition limits the rapid degradation of the films and preserves their superconducting properties
Knittel, Stéphane. "Elaboration et caractérisation du comportement en oxydation d'alliages composites à base de niobium et de siliciures de type M7Si6 et M8Si7 envisagés comme revêtements protecteurs". Thesis, Nancy 1, 2011. http://www.theses.fr/2011NAN10127/document.
Texto completoThe improvement of the efficiency of turbine engine can be achieved by increasing the working temperature. The development of new alloys based on Nb-Si system allows a jump of 200°C of the operating temperature in comparison to that offered by current nickel based alloys. The first part of this manuscript focuses on the evolutions which have led to the development of niobium silicide in situ composites (Nbss-Nb5Si3). The microstructure of these alloys consists in a ductile niobium matrix where number of alloying elements can solubilise and of strengthening niobium silicides which are intended to provide creep and oxidation resistance at high temperature. Unfortunately, these alloys exhibit a poor oxidation resistance characterised by a high metal recession rate and the formation of non-protective oxide scale. Thus, oxygen can easily react with the substrate, dissolve in Nbss and diffuse quickly through this phase. The effect of Al, Si and Ti additions on both microstructure and oxidation resistance were investigated. Although, these composition optimisations lead to a significant enhance of oxidation resistance, some compositions still suffers from catastrophic oxidation behaviour around 800°C. In these alloys tin additions involve high microstructural changes, especially by initiating the formation of A15- Nb3Sn phase. At 800°C, Sn additions suppress oxygen dissolution in Nbss responsible of the catastrophic oxidation behaviour of these alloys. Nevertheless, the oxidation resistance of these alloys remains too low for the foreseen applications and protective coatings are required. Thermodynamic stability and oxidation resistance of two silicide families (Nb3X3CrSi6 and Nb4X4Si7 (X = Fe, Co or Ni)) were investigated. These silicides have exhibited a high oxidation resistance up to 1300°C by the formation of a protective silica layer. Finally, these silicides were deposited on Nbss-Nb5Si3 substrate by using the pack cementation process. Some coated alloys have then exhibited lifetime going up to 3000 one hour cycle at 1100°C
Saxey, David W. "A high-resolution superconducting pressure gauge and irreversible magnetic effects in Nb and NbTi wires". University of Western Australia. School of Physics, 2005. http://theses.library.uwa.edu.au/adt-WU2005.0007.
Texto completoShrestha, Sachin. "Characterising the effect of Niobium-rich clusters on the microstructure-property relationships in CASTRIP® steels". Thesis, The University of Sydney, 2013. http://hdl.handle.net/2123/10297.
Texto completoSeemüller, Hans Christoph Maximilian [Verfasser] y M. [Akademischer Betreuer] Heilmaier. "Evaluation of Powder Metallurgical Processing Routes for Multi-Component Niobium Silicide-Based High-Temperature Alloys / Hans Christoph Maximilian Seemüller. Betreuer: M. Heilmaier". Karlsruhe : KIT-Bibliothek, 2016. http://d-nb.info/1100529713/34.
Texto completoTalbot, Diane. "The effects of plate processing parameters on the microstructure, mechanical properties and precipitation characteristics of niobium-containing high strength low alloy steels". Thesis, University of Birmingham, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.251877.
Texto completoSeemüller, Hans Christoph Maximilian [Verfasser] y Martin [Akademischer Betreuer] Heilmaier. "Evaluation of Powder Metallurgical Processing Routes for Multi-Component Niobium Silicide-Based High-Temperature Alloys / Hans Christoph Maximilian Seemüller. Betreuer: M. Heilmaier". Karlsruhe : KIT-Bibliothek, 2016. http://nbn-resolving.de/urn:nbn:de:swb:90-544644.
Texto completoBellavoine, Marion. "Transformations de phases et recristallisation dans les aciers Dual Phase microalliés au titane niobium : étude expérimentale et modélisation". Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0262.
Texto completoTo meet the need for weight reductions in the automotive industry, new advanced high-strength steels are being developed. The achievement of a better balance between high strength and high formability requires a deep understanding of both the effect of chemical composition and processing parameters on the formation of microstructures. The present work contributes to such an objective and deals with the mechanisms occurring during annealing of Dual Phase steels microalloyed with Ti and Nb. Microstructural changes during this stage include precipitation of microalloying elements, ferrite recrystallization and austenite formation. These mechanisms are investigated using complementary experimental techniques at different scales such as in situ XRD, SEM, TEM and APT in various Dual Phase steel grades having the same bainite-martensite initial cold-rolled microstructure. Using combined experimental and modeling approaches, the present work clarifies the separate influence of microalloying elements Ti, Nb and Mo and heating rate on the mechanisms occurring during annealing and their interactions
Croteau, Jean-François. "Single crystal and polycrystalline niobium and OFE copper for SRF cavities applications : mechanical characterization at low to high strain rates and microstructural investigations". Thesis, Brest, École nationale supérieure de techniques avancées Bretagne, 2021. http://www.theses.fr/2021ENTA0006.
Texto completoManufacturing of superconducting radiofrequency (SRF) cavities with high performances is paramount to increase the collision energy in new particle accelerators. The use of high-speed sheet forming techniques, such as electro-hydraulic forming, can be beneficial, but requires a detailed understanding of the mechanical properties of the materials being deformed and the consequence on their microstructure. This thesis focuses on the characterization of high-purity niobium single crystals, polycrystalline niobium sheets, and polycrystalline OFE copper sheets. The results from this study are separated in two parts. In Part I, the characterization of niobium single crystals focused on the mechanical properties in tension and compression at strain rates of 10-4 to 103 s-1 and on the microstructure (analyzed using SEM, EBSD, TEM, and nanoindentation) of the deformed specimens. The effect of crystal orientation, strain rate, and loading direction on the mechanical properties, the crystal rotation, and the dislocation substructures are presented. In Part II, the forming limit diagram (FLD) of polycrystalline niobium sheets and OFE copper sheets were measured at a quasi-static strain rate. The FLDs of those materials should provide important data for manufacturers using conventional techniques, such as deep-drawing and spinning. The second part also presents the mechanical properties of electron beam (EB) welded polycrystalline niobium sheets and OFE copper sheets deformed in tension and compression at strain rates of 10-3 to 103 s-1
Philippot, Clément. "Etude des mécanismes de précipitation, de recristallisation et de transformation de phases dans les aciers Dual Phase microalliés au titane niobium lors du recuit". Thesis, Aix-Marseille, 2013. http://www.theses.fr/2013AIXM4342.
Texto completoLightening the weight of vehicles is one of the main challenging objectives of the automotive industry to reach the environmental regulation in term of CO2 emissions. The development of multiphase high strength steels is a common solution to reduce the thickness of sheet steel used in vehicles while keeping the same level of passenger’s safety requirements. The present study deals with the optimization of industrial process parameters applied to obtain one of these steels: the high strength microalloyed Dual Phase steels; i.e. with ultimate tensile strength superior to 800MPa.From an initial cold rolled microstructure made of bainite + martensite, the phenomena occurring during the annealing are characterized since the heating up to the end of the intercritical holding. The influence of process parameters as the heating rate, the holding temperature and the holding time are studied. The triple interactions system between the precipitation of microalloying elements, the recrystallization and the austenite formation is the core of the problem. A scenario of microstructural evolutions has been established based on the characterized phenomena. The studied fine microstructure (sub-microns) requires the combination of multiscale characterization techniques: SEM, TEM, atom probe tomography, nano-SIMS
Kisko, A. (Anna). "Microstructure and properties of reversion treated low-Ni high-Mn austenitic stainless steels". Doctoral thesis, Oulun yliopisto, 2016. http://urn.fi/urn:isbn:9789526212159.
Texto completoTiivistelmä Väitöstyössä tutkittiin reversiohehkutuksen vaikutusta metastabiilin 1% nikkeliä ja 9% mangaania sisältävien austeniittisten ruostumattomien terästen mikrorakenteeseen ja mekaanisiin ominaisuuksiin sekä austeniitin raekoon ja mikrorakenteen vaikutusta muokkausmartensiitin syntyyn vetokokeessa. Koeteräksistä osa oli lisäksi niobiseostettuja. Tavoitteena oli nostaa teräksien lujuutta ja ymmärtää ultrahienorakeisen austeniittisten ruostumattomien terästen käyttäytymistä muokkauksessa. Teräkset kylmämuokattiin 60% valssausreduktiolla, jolloin austeniittiseen rakenteeseen muodostui muokkausmartensiittia enimmillään 60%. Reversiohehkutukset tehtiin Gleeble termomekaanisella simulaattorilla lämpötiloissa 450–1100 °C ja 0.1–1000 s pitoajoilla. Saatuja mikrorakenteita tutkittiin eri tutkimuslaitteistoilla ja -menetelmillä. 700 °C hehkutuksessa leikkautumalla ja diffuusion välityksellä tapahtuva reversio oli nopea myös niobi-seostetuilla teräksillä, mutta rekristallisaatiota ei tapahtunut. 800 °C hehkutuksessa muokkauksessa teräksiin jäänyt austeniitti rekristallisoitui, mutta raerakenne muodostui epätasaiseksi koostuen reversion tuottamasta ultrahienoista rakeista ja jäännösausteniitin rekristallisaation tuottamista karkeammista rakeista. Sitä vastoin hehkutus 900 °C:ssa tuotti tasainen 2 μm austeniitin raekoon. Pitkissä hehkutuksissa korkeammissa lämpötiloissa 1000–1100 °C niobi-seostamattomissa teräksissä tapahtui hienojen rakeiden normaalia rakeenkasvua. Kuitenkin 0.28p-% niobi-seostuksen havaittiin oleva riittävä estämään rakeenkasvu. Reversion ja osittaisen rekristallisaation tuottamilla raerakenteilla saatiin erinomaiset myötölujuus-tasavenymäyhdistelmät. Vetokokeissa martensiitin ydintymispaikat ja -nopeus vaihtelivat monimutkaisella tavalla raekoosta riippuen
Georges, Cédric. "Improvement of the mechanical properties of TRIP-assisted multiphase steels by application of innovative thermal or thermomechanical processes". Université catholique de Louvain, 2008. http://edoc.bib.ucl.ac.be:81/ETD-db/collection/available/BelnUcetd-08232008-100716/.
Texto completoJimenez, Tejeda Kety Mayelin. "Design, development, and characterization of thin-film filters for high brilliance sources in the EUV-soft x-ray spectral range". Doctoral thesis, Università degli studi di Padova, 2019. http://hdl.handle.net/11577/3425436.
Texto completoKeys, Simon Alastair. "Temperature and strain scaling laws for the critical current density in Nb(_3)Sn and Nb(_3)Al conductors in high magnetic fields". Thesis, Durham University, 2001. http://etheses.dur.ac.uk/3951/.
Texto completoCyrille, Marie-Claire. "Étude et réalisation de SQUIDS à polarisation continue pour l'amplification radiofréquence à très faible température de bruit". Université Joseph Fourier (Grenoble ; 1971-2015), 1996. http://www.theses.fr/1996GRE10228.
Texto completoCastro, Danilo Borges Villarino de. "Estudo do comportamento em fadiga do aço ASTM A297 Gr HP modificado com nióbio em altas temperaturas". Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/88/88131/tde-20122012-092456/.
Texto completoThis work aims to study the mechanical behavior at high temperatures of ASTM A-297 Gr HP steel changed with niobium. This type of steel is used for pipe supports that remain exposed long periods of time at operating temperatures near 900°C. In this study, was studied the microstructural composition, the mechanical strength, impact toughness and fatigue resistance, considering the effect of temperature test. To evaluate the effect of temperature and residence time in the microstructure and hence the mechanical properties were performed hardness, tensile and impact test for each of the conditions presented. All conditions of the aged material showed the presence of precipitates in the interdendritic boundaries and secondary precipitates within the austenitic matrix, causing the material to elevate its mechanical strength, compared to CR condition. After this step was studied the mechanical properties at elevated temperatures only for the conditions CR and T1000 (aged at 927°C for 1000 hours). Tensile, impact and fatigue tests (E-N and da/dN-\'delta\'K), were performed at the following temperatures: 25°C, 871ºC, 899ºC, 927ºC, 954ºC and 982°C. To evaluate the impact tests, were used Charpy specimens of the conventional type (presence of the notch) and pre-cracked (pre crack more notch). In all test temperatures of traction, it was observed that the T1000 condition resulted in an increase of the value of mechanical strength and reduction of its ductility, compared to CR conditions. In tests at elevated temperatures, it was observed that the precipitation of carbides in the austenitic matrix of the secondary condition T1000 is able to avoid a sharp decline in mechanical strength compared with the proviso CR. The two conditions (CR and T1000) were sensitive to the presence of a stress raiser (notch further pre-crack) when subjected to impact tests. The results of tensile and impact fractographies corroborate the evidence found for each condition, indicating a greater share of ductile fracture in testing samples at elevated temperatures than at room temperature. Regarding the fatigue behavior of the material, it was found that the fatigue life of the material tested at 25°C was much greater than 927°C, especially in the region of high cycle fatigue. This fact can be attributed to two factors dependent on the time: premature nucleation due to a significant reduction in yield strength and due to the effect of surface oxidation of permanent slip bands. The tests of crack propagation by fatigue showed that the rate da/dN was greater at a temperature of 927°C than at 25°C, because of higher ductility that the material exhibits at high temperatures associated with the effects of oxidation and creep.
Penagos, Jose Jimmy. "Efeito do refinamento da microestrutura e da adição de nióbio na resistência ao desgaste abrasivo de ferros fundidos de alto cromo". Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/3/3151/tde-25082016-082141/.
Texto completoHigh Chromium Cast Irons (HCCI\'s), because of their excellent tribological properties, have been widely used for specific applications involving high wear rates by abrasion, especially in the mining sector. However, the demand for materials with higher wear resistance is continuously growing and thus further research is needed in this area. For that reason, the current work purposes to assess the use of niobium to further increase the wear resistance of HCCI\'s. On the other hand, when HCCI is used for manufacturing components with irregular geometries (e.g. pump impellers), the components thin and thick regions can contain different levels of structure refinement due to variation in their cooling rates. In this work, the effect of structure refinement and the interaction between structure refinement and niobium addition on the abrasion resistance of HCCI\'s were evaluated. For that purpose, four systematic main studies were developed: in the first study, blocks of HCCI were manufactured varying the structure refinement and it was shown that large increases in the degree of structure refinement result in higher wear mass losses by abrasion. In less refined microstructures, the larger M7C3 chromium carbides are less susceptible to microcracking and can occasionally act as a barrier to abrasive particles. In the second series of experiments, the interaction between structure refinement and niobium addition in low concentrations (1 %) was evaluated; showing that for more refined microstructures, niobium additions reduce the mass losses by abrasion up to 50 %. In the third series of experiments, the interaction between niobium and molybdenum additions was evaluated. Compared to molybdenum-free alloy, simultaneous additions of niobium and molybdenum resulted in a more refined microstructure, higher hardness of the matrix and harder niobium carbides (NbC). For Low Stress Sliding Abrasion (LSSA) wear configuration, where wear was more pronounced in the matrix, simultaneous addition of niobium and molybdenum resulted in increase of abrasion resistance in the studied HCCI. In the last stage of this work, 3 % of niobium were added in an HCCI alloy with hypereutectic initial chemical composition (25%Cr/3%C), which presents primary large sized chromium carbides that induce a brittle behavior of the HCCI when subjected to wear. However, the niobium addition resulted in a more refined microstructure (eutectic) HCCI containing compact-shaped NbC carbides, and consequently in more resistance to abrasive wear.
Alves, Gabriel Godinho. "Recristalização do aço ARBL microligado ao nióbio CSN 2336". Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/97/97134/tde-27092012-120450/.
Texto completoThe recrystallization of a high strength low alloy steel (HSLA) containing niobium (160 wt-ppm) was investigated. The HSLA steel, named CSN 2336, is used in the manufacture of structural parts for automotive industry. The increasing use of this application type of steels in automotive industries has motivated the development of new alloys able to gather the critical requirements for deep drawing combined with high strengths. Samples of this steel in hot-rolled condition were cold-rolled with reductions of 50% and 70%, commonly used in most of applications, and isothermally annealed in salt bath at temperatures between 600 and 700ºC. The microstructure of the samples in both coldworked and annealed states was imaged using light optical (LOM) and scanning electronic microscopies (SEM). Deformation and recrystallization textures were determined by X-ray diffraction. The recrystallized volume fraction (Xv) and the mean grain size were determined by quantitative metallography in the annealed samples. Vickers microhardness testing was used to determine the work hardening and the softening kinetics behaviors. The results show that recrystallization occurs at temperatures above 650°C for the most deformed steel. By plotting Xv against A (softening fraction), we observe the occurrence of a deviation from ideality at 650°C and 700°C, likely caused by solid-state precipitation, especially for the less deformed steel. The values of n (Avrami exponent) obtained from both approaches (softening curves and quantitative metallography) are presented and discussed.
Oliveira, Tarciso Mesquita de. "Picos da magnetização em supercondutores do tipo II". [s.n.], 2005. http://repositorio.unicamp.br/jspui/handle/REPOSIP/278497.
Texto completoDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataglin
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Resumo: Nesta tese estudamos possíveis origens do Segundo Pico da Magnetização (SPM) em supercondutores de alta e baixa temperatura crítica, usando amostras monocristalinas de Bi2Sr2CaCu2O8+d e de Nb. Para estudar o SPM fizemos medidas de curvas de magnetização M x H e suscetibilidade AC (vs. h e T). Através da aplicação de uma lei de escala, para suscetibilidade AC, obtivemos o expoente de creep na região do SMP. Em amostras de Nb verificamos os efeitos sobre as curvas M x H de não homogeneidades na amostra: deslocamentos de planos e oxigênio intersticial. Em amostras de alta pureza (bulk e monocristalina) observamos que as curvas M x H não apresentam o SPM nem o Efeito Pico, próximo a Hc2.Ao adicionar não homogeneidades nas amostras, através de dopagem com oxigênio e deformação por elongação, observamos o aparecimento do Efeito Pico, de instabilidades termomagnéticas e de anisotropia do campo Hc2. Em amostras de Bi2Sr2CaCu2O8+d observamos que o SPM está associado com a componente do campo aplicado paralela à direção c da rede cristalina, ou seja, que o SPM está relacionado com vórtices de Abrikosov e que vórtices Josephson parecem não influenciar no SPM. Ao clivarmos a amostra observamos que a intensidade do SPM se reduz e diminui a janela de temperatura onde ele é visto. Obtivemos o expoente de creep e observamos que na região do SPM o arrasto dos vórtices diminui em campos que antecedem o HSPM , mas na região de HSPM o arrasto aumenta rapidamente e depois volta a cessar. Interpretamos a variação brusca no expoente de creep como uma mudança de fase no sistema de vórtices, que passa de um estado de quase-rede para um estado emaranhado de vórtices
Abstract: In this thesis we have studied possible origins for the Second Magnetization Peak (SMP) in high and low critical temperature superconductors, using samples of Bi2Sr2CaCu2O8+d and Nb single crystals. To study the SMP we did measurements of magnetization curves (M x H) and AC susceptibility (vs. h and T). We obtained the creep exponent in the SMP region, using a scaling law for the AC susceptibility data. In the Nb samples we have verified the effects on M x H curves due to inhomogeneities like dislocations and interstitial oxygen. In high pure samples (bulk and single crystals) we have observed that the M x H curves do not present either SMP or Peak Effect, near H2c . By adding inhomogeneities in the samples, like doping them with oxygen or deforming by elongation, we have observed the appearance of Peak Effect, thermomagnetic instabilities, and H2c anisotropy. In Bi2Sr2CaCu2O8+d samples we have observed that the SMP is associated with the magnetic field component parallel to the crystal c direction of crystal net. This means that the SMP is related to Abrikosov¿s vortices and that Josephson¿s vortices seem not to influence the SMP. After cleaving the sample we observed that the SMP intensity was reduced and the temperature window were it occurs was decreased. We have obtained the creep exponent and have observed that in the SMP region the vortices creep diminish for fields below HSPM , but around HSPM the creep increases abruptly and after the SPM it decreases again. We have interpreted the abrupt creep exponent variation as a phase transition in the vortex system, that pass from a quasi-lattice state to an entangled vortex state
Mestrado
Física
Mestre em Física
TERNER, MATHIEU. "Innovative materials for high temperature structural applications: 3rd Generation γ-TiAl fabricated by Electron Beam Melting". Doctoral thesis, Politecnico di Torino, 2014. http://hdl.handle.net/11583/2527509.
Texto completoRuiz, Alberto Ibañez. "A presença do nióbio em um ferro fundido branco de cromo-molibdênio: traçado da curva transformação-tempo-temperatura". Universidade de São Paulo, 1996. http://www.teses.usp.br/teses/disponiveis/18/18136/tde-09102017-142618/.
Texto completoIn this work we studied the hardenability of high chromium- molibdenum white cast iron with niobium. By dilatometry we obtained the TTT curve of this material as well as the high chromium white cast iron for comparison. This comparison and available results in literature confirm the high temperability of experimental material. We can use slow rate cooling 0,12°C/s or higher without phase transformation, while in the comparative alloy this rate is around 5,8°C/s or higher from specific used austenitic abrasive temperature. We also realized analysis of abrasive wear, hardness and microhardness, raios-X difraction, magnetic phase and microanalyse for verifing the phase transformation as observed by dilatometry. The structure variation as function of termic treatment in both alloys is monitored by optical microscope. The present work indicate that the material under study can offer more flexibility for projects with thick materials apart from intrinsic characteristics of abrasive wear and corrosion.
Silva, Cloir Salatiel da. "Análise microestrutural em altas temperaturas de um ferro fundido branco de alto cromo com molibdênio e nióbio". Universidade de São Paulo, 1999. http://www.teses.usp.br/teses/disponiveis/88/88131/tde-14092016-124243/.
Texto completoThe microstructural changes caused by the addition of alloying elements and by thermal treatments modify the mechanical and tribological properties of the materials. A study was develop on samples of molybdenum and niobium high chromium white cast iron, trying to determine the effects of molybdenum and niobium alloys elements on microstructure of this material through hardness measurements, dilatometry, chemical etching, scanning electron microscopy, and mainly, utilizing metallography at high temperatures. The metallography at high temperatures technic allows the study of microstructural changes during the thermal cyc1es, which were scheduled, having as reference the TTT curve previously traced to this material, focusing regions where changes of fase don\'t occur. So the metallographic appearances at high temperatures were obtained and it was done a comparative study using other technics. Because of that is possible to improve the knowledge of the material microstructure, which it has been studied, and to obtain alloys with predetermined properties.
Griffith, Kent Joseph. "Atomic and electronic structure of complex metal oxides during electrochemical reaction with lithium". Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/271191.
Texto completoSilva, J?nior Jos? Ferreira da. "Comportamento da adi??o do carbeto de ni?bio (nBC) na matriz met?lica do a?o ferr?tico 15kH2mfa". Universidade Federal do Rio Grande do Norte, 2012. http://repositorio.ufrn.br:8080/jspui/handle/123456789/12804.
Texto completoConselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico
The 15Kh2MFA steel is a kind of Cr-Mo-V family steels and can be used in turbines for energy generation, pressure vessels, nuclear reactors or applications where the range of temperature that the material works is between 250 to 450?C. To improve the properties of these steels increasing the service temperature and the thermal stability is add a second particle phase. These particles can be oxides, carbides, nitrites or even solid solution of some chemical elements. On this way, this work aim to study the effect of addition of 3wt% of niobium carbide in the metallic matrix of 15Kh2MFA steel. Powder metallurgy was the route employed to produce this metallic matrix composite. Two different milling conditions were performed. Condition 1: milling of pure 15Kh2MFA steel and condition 2: milling of 15Kh2MFA steel with addition of niobium carbide. A high energy milling was carried out during 5 hours. Then, these two powders were sintered in a vacuum furnace (10-4torr) at 1150 and 1250?C during 60 minutes. After sintering the samples were normalized at 950?C per 3 minutes followed by air cooling to obtain a desired microstructure. Results show that the addition of niobium carbide helps to mill faster the particles during the milling when compared with that steel without carbide. At the sintering, the niobium carbide helps to sinter increasing the density of the samples reaching a maximum density of 7.86g/cm?, better than the melted steel as received that was 7,81g/cm?. In spite this good densification, after normalizing, the niobium carbide don t contributed to increase the microhardness. The best microhardness obtained to the steel with niobium carbide was 156HV and to pure 15Kh2MFA steel was 212HV. It happened due when the niobium carbide is added to the steel a pearlitic structure was formed, and the steel without niobium carbide submitted to the same conditions reached a bainitic structure
O a?o 15Kh2MFA, da fam?lia dos a?os CrMoV, pode ser utilizado em turbinas para gera??o de energia, vasos de press?o, reatores nuclear ou aplica??es, onde o material ? submetido a temperaturas de servi?o entre 250 e 450?C. Uma forma de melhorar as propriedades do a?o, para que ele trabalhe a temperaturas mais altas ou que se torne mais est?vel ? adicionar part?culas de segunda fase na sua matriz. Estas part?culas podem estar na forma de ?xidos, carbetos, nitretos ou at? mesmo em solu??o s?lida quando alguns elementos qu?micos s?o adicionados ao material. Neste contexto, este trabalho objetiva estudar o efeito da adi??o de 3% de carbeto de ni?bio na matriz met?lica do a?o 15Kh2MFA. Para isto a metalurgia do p? foi a rota empregada para a produ??o deste comp?sito de matriz met?lica. Para tal, duas moagens distintas foram realizadas. A primeira com o a?o 15Kh2MFA e a segunda com o a?o 15Kh2MFA com adi??o de 3% de carbeto de ni?bio. A moagem de alta energia foi realizada durante 5 horas. Em seguida, os dois p?s produzidos foram sinterizados em um forno a v?cuo (10-4torr) a temperaturas de 1150?C e 1250?C durante 60 minutos. Ap?s a sinteriza??o as amostras foram submetidas ao tratamento t?rmico de normaliza??o a 950?C. Os resultados mostraram que a adi??o do carbeto de ni?bio ajuda o processo de cominui??o das part?culas, quando comparado com o a?o sem o carbeto de ni?bio. O carbeto de ni?bio tem um papel fundamental na densifica??o das amostras durante a sinteriza??o, levando a densidade 7,86g/cm?, que ? maior do que a densidade do a?o fundido recebido que era de 7,81g/cm?. Apesar desta boa densifica??o, ap?s a normaliza??o, o NbC n?o contribuiu de forma significativa para aumento da dureza, onde a melhor dureza obtida para o a?o com NbC foi de 156HV e para o a?o puro foi de 212HV. Isto se deve ao fato de que, quando o NbC foi adicionado ao a?o, formou-se uma estrutura perl?tica, enquanto que, com o a?o sem adi??o de NbC, submetido as mesmas condi??es, obteve-se uma estrutura bain?tica
Fernández-Arroyo, Naranjo Alberto. "CATALYTIC TRANSFORMATIONS OF OXYGENATED COMPOUNDS DERIVED FROM BIOMASS AQUEOUS EFFLUENTS INTO HIGH-VALUE PRODUCTS". Doctoral thesis, Universitat Politècnica de València, 2018. http://hdl.handle.net/10251/110080.
Texto completoThe valorisation of lignocellulosic biomass and its derivatives has become a sustainable alternative to the use of fossil sources for the production of fuels and chemicals. In this context, the conversion of light oxygenated compounds present in aqueous effluents derived from primary treatments of biomass (i.e. fast pyrolysis), after a phase separation process via water addition is a key step in the actual bio-refinery scheme processes. The strategy is based on the transformation of these low-value water-soluble oxygenated compounds into a mixture of hydrocarbons and aromatics useful for blending with automotive fuels. In general, the activity of the catalysts employed in these processes is based on their bifunctional character. Nonetheless, their activity in complex aqueous mixtures and their stability under faithful operating conditions close to industrial scenarios are critical challenges to be further applied. This thesis comprises a detailed work in the design of new solid catalysts with high activity and stability in consecutive aqueous-phase condensation reactions of light oxygenated compounds (C1-C4) mixtures under moderated process conditions. In this sense, this work differs from usual probe molecules studies performed even in the absence of water. Firstly, mixed oxides (including CexZr1-xO and hydrotalcite-derived materials) were employed as they have been widely studied in condensation and ketonization reactions. These materials show good catalytic results in the liquid-phase condensation of light oxygenates, but strong catalysts deactivation was observed due to the active phase partial leaching. Therefore, new heterogeneous acid catalysts must be developed in order to meet these new process requirements: complex aqueous environments with high contents of organic acids and moderated reaction conditions. In this sense, the addition of aqueous HF during TiO2 catalysts synthesis is essential to selectively control the preferential growth of catalytic more reactive {001} TiO2 facets. Moreover, Lewis acid sites on faceted TiO2 materials have great stability in condensation reactions, especially in the presence of organic acids and high water contents. Thus, this strategy allows obtaining materials that show better catalytic results and stability than other commercial titanium oxides. Moreover, hydrothermal synthesized Nb- and WNb-mixed oxides have shown the advantage of having crystalline structure, area and acid properties modified by tailoring their composition and post-synthesis heat-treatments conditions. Optimized NbOx and WNbO materials show higher activity and stability in the aqueous-phase condensation of oxygenated compounds than other commercial samples, commonly employed in literature Finally, new acid catalysts prepared via co-precipitation based on tin, titanium and niobium (SnxTiyNbzO) mixed oxides have been developed. These materials mainly present SnO2 rutile-phase crystalline structure, which has been claimed to have interesting hydrophobic characteristics. Tailoring of composition and calcination conditions allows obtaining mixed oxides with uniform crystalline structures, enhanced surface areas and a higher concentration of Lewis acid sites compared to analogous commercial catalysts. These materials show high activity and stability in the valorisation of oxygenated compounds present in aqueous effluents derived from different biomass processes.
La valorització de biomassa lignocel·lulòsica i dels seus derivats suposa una alternativa sostenible enfront de la utilització de fonts fòssils per a la producció de combustibles i productes químics. En aquest context, l'aprofitament de compostos oxigenats presents en efluents aquosos derivats de tractaments primaris de la biomassa (via piròlisi ràpida), després d'un procés de separació de fases, és fonamental en l'esquema actual de bio-refineria. L'estratègia consisteix a transformar aquests compostos orgànics en mescles d'hidrocarburs i compostos aromàtics d'utilitat com a components o additius en combustibles líquids. Els materials catalítics comunament estudiats per a aquest tipus de processos deuen l'activitat a les seues propietats multifuncionals; no obstant això, la seua activitat en mescles aquoses complexes i la seua estabilitat sota condicions de reacció més pròximes a la realitat industrial continuen sent un desafiament amb vista a la seua futura aplicació. La present tesi doctoral se centra en el disseny de nous catalitzadors heterogenis que siguen actius i resistents en reaccions de condensació consecutives en fase aquosa de mescles de compostos oxigenats lleugers (C1-C4) sota condicions de reacció moderades. En aquest sentit, aquest treball difereix dels estudis habituals, que empren compostos model de forma individual i en absència d'aigua. En primer lloc, òxids mixts (inclosos CexZr1-xO i hidrotalcites), que han sigut àmpliament utilitzats en reaccions de condensació i cetonització, mostren bons resultats catalítics en la condensació en fase aquosa, però greus problemes d'estabilitat a causa principalment de la lixiviació de la fase activa d'aquests materials. Això demostra la necessitat de desenvolupar nous catalitzadors àcids capaços d'operar en sistemes complexos en presència d'aigua i àcids orgànics, sota condicions de reacció moderades. En aquest sentit, l'addició d'HF durant la síntesi de catalitzadors basats en TiO2, permet obtenir materials on s'exposa majoritàriament el plànol {001}, que és catalíticament més actiu. A més, els llocs àcids de Lewis presents en aquests materials de TiO2 facetats, presenten una gran estabilitat en reaccions de condensació, especialment en presència d'àcids i grans quantitats d'aigua. Aquesta estratègia permet desenvolupar materials amb millor activitat catalítica i estabilitat que altres catalitzadors comercials basats en TiO2. D'altra banda, la síntesi hidrotermal d'òxids metàl·lics basats en Nb i W-Nb permet obtenir materials l'estructura cristal·lina, les propietats texturals i les propietats àcides dels quals poden ser modificats controlant la composició i les condicions de calcinació aplicades. Això permet obtenir catalitzadors optimats respecte als emprats en la literatura, que mostren gran activitat i elevada estabilitat en reaccions de condensació de compostos oxigenats en fase aquosa. Finalment, s'han desenvolupat nous materials basats en òxids mixts d'estany, titani o niobi (SnxTiyNbzO) preparats per coprecipitació, que presenten majoritàriament l'estructura tipus rútil del SnO2, la qual té característiques hidròfobes. El control de la composició i les condicions de calcinació permeten obtenir òxids amb estructures cristal·lines uniformes, altes àrees superficials i major densitat de llocs àcids de Lewis respecte als respectius òxids comercials. Aquests materials són catalitzadors actius i molt resistents en la valorització de compostos oxigenats presents en efluents aquosos derivats de diferents tractaments de la biomassa.
Fernández-Arroyo Naranjo, A. (2018). CATALYTIC TRANSFORMATIONS OF OXYGENATED COMPOUNDS DERIVED FROM BIOMASS AQUEOUS EFFLUENTS INTO HIGH-VALUE PRODUCTS [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/110080
TESIS
Kesani, Sheshanka. "Sol-gel Niobia-based Sorbents for the Enrichment of Organophosphorus Compounds by Capillary Microextraction Online Coupled to High Performance Liquid Chromatography". Scholar Commons, 2017. https://scholarcommons.usf.edu/etd/7413.
Texto completoChang, HsiaoTzu y 張孝慈. "The research of high temperature property of Niobium alloy". Thesis, 2003. http://ndltd.ncl.edu.tw/handle/89284891123069775556.
Texto completo國立臺灣大學
材料科學與工程學研究所
91
Intermetallic Nb3Al alloy with high melting temperature, appropriate density and excellent high temperature strength is expected to be a structural material operated above 1000℃. These alloys attract more attention for aerospace application in the past decade. Although Nb3Al possesses excellent high temperature strength, it has poor fracture toughness at ambient temperature. Combining a ductile Nbss phase with brittle Nb3Al phase may improve the fracture toughness of the alloy, but leads to a decrease in high temperature strength. The goal of this research is to investigate the effect of Ni addition on the mechanical property, oxidation and corrosion resistance of the Nb-Al alloy at high temperature. To realize the high temperature oxidation and corrosion property, a commercial niobium alloy, C103 (Nb-10Hf-1Ti), was used to compare with the properties of Nb-Al alloy in this experiment. Moreover, a plasma sprayed coating was conducted on all alloys to improve their high temperature oxidation and corrosion resistance. The result of compression test reveals that the addition of nickel to Nb alloy reduces the DBTT (ductile-brittle transition temperature) of Nb3Al alloy, increases the ductility, and improves its high temperature strength. Besides, the addition of 5 at.% Ni could also supply the alloy with an outstanding oxidation and corrosion resistance. However, when the addition of nickel exceeds 5 at.%, the oxidation resistance property will deteriorate. The experimental results show that the plasma spraying coating may efficiently improve the high temperature oxidation and corrosion resistance of the alloy.
Vachirapatama, Narumol. "Separation and determination of niobium(V) and tantalum(V) by reversed-phase high-performance liquid chromatography". Thesis, 2000. https://eprints.utas.edu.au/22046/1/whole_VachirapatamaNarumol2000_thesis.pdf.
Texto completoTsao, Tzu-Ching y 曹梓敬. "Investigation of Strain-induced Precipitation Behavior of Niobium Micro-alloyed Steels at High Temperature". Thesis, 2019. http://ndltd.ncl.edu.tw/handle/zw3vd5.
Texto completo國立臺灣大學
材料科學與工程學研究所
107
The strain-induced precipitation behavior of niobium micro-alloyed steels at high temperature has been studied in this research. Based on the difference of niobium content and aluminum/nitrogen ratio, the precipitation time, precipitates size, recrystallization and structure of martensite after quench have been analyzed. After austenization treatment, and redissolving precipitates, materials were subjected to 25% compression deformation, and then held at the temperature we designed. According to the second compression deformation after different holding time, the degree of recrystallization of materials can be known and used to predict the time that precipitation started, and the precipitation-start time-temperature(PSTT) curve was obtained. Results reveal that different niobium content and aluminum/nitrogen ratio show little effect on the start time of precipitation. The nose tip of PSTT curve is approximately in the range of 875~900℃ and 1~3 second. 900℃ was chosen to be the best work temperature and the temperature for analysis because materials showed good softening resistance, slow recrystallization and early precipitation time at 900℃. Follow-up analysis shows that when niobium content is high, the size of precipitates become larger, and indication of coarsening can be observed at early stage of precipitation. Metallography also reveals that recrystallization happens more obviously when niobium content is high, indicating that more niobium may cause faster coarsening of precipitates. Aluminum/nitrogen ratio shows little effects on softening resistance in the time we designed; however, coarsening which occurred at late stage indicates that it may be detrimental for keeping precipitates small if the excess nitrogen form carbonitride with niobium. Fully lath martensite was obtained after quench from austenite in experimental material, not only general martensite lath but auto-tempered martensite and interpenetrating twin were able to be observed in the microstructure. Auto-tempered martensite forms from the sub-blocks which formed at high temperature. The lathes which belong to the same variant possess similar orientation relationship between each other, so when thermal energy is enough to adapt the small angle boundary, martensite will be coarsening. Because there was no high carbon region after heat treatment, the twin structure in the microstructure is interpenetrating twin instead of plate martensite. Interpenetrating twin forms from some lathes which naturally possess twin orientation relationship between each other. If the twin-relation lathes contact at the boundary of blocks, these lathes which formed at high temperature may penetrate each other to form interpenetrating twin.
Yu, Chen-Ping y 游振平. "The influence of niobium-additive and heat treatment on the hydrogen embrittlement of ultra-high strength boron steel". Thesis, 2014. http://ndltd.ncl.edu.tw/handle/33948157072106400308.
Texto completo國立臺灣大學
材料科學與工程學研究所
102
15B30 steel, an ultra-high strength boron steel, has 2000MPa ultra-high tensile strength in martensitic state. Due to its high strength property, 15B30 steel is best used in structural steel and automotive plate. However, ultra-high strength steel is prone to hydrogen embrittlement in practical usage, which will lead to severe unpredictable fracture. The aims of this research are to build up an evaluation method of hydrogen embrittlement and find the effects niobium-additive and heat treatment on the hydrogen embrittlement of 15B30 steel. After chemical hydrogen charging, the as-quenched 15B30 exhibits the worst resistance of hydrogen embrittlement. Its percentage loss of UTS after hydrogen charging is about 70%, and the fractography is intergranular fracture. Through tempering processes in different temperatures, it is found that 200℃ tempering processing is effective to resist the hydrogen embrittlemet. This feature is mainly ascribed to the ε carbide precipitates in the martensite lath, which can provide additional hydrogen trapping site. The cementite will precipitate along martensite lath interface and prior austenite grain boundary during the tempering at 300℃ and 400℃. This type of hydrogen trapping sites lead to a weaker resistance to hydrogen embrittlement. Niobium-added 15B30, namely the 15B30Nb steel, can have the refined grains due to the existence of (Nb,Ti)(CN) and NbC precipitates. These refined grains could improve noticeably the hydrogen embrittlement resistance in the tempering state. Constant load test shows that the hydrogen pre-charged 15B30Nb steel could sustain a longer fracture time, which also reveals that the refined grains have better hydrogen embrittlement resistance.
Chen, Yu-Wen y 陳昱文. "Investigation on the Synergistic Effect of Niobium Composite Carbide in Low Carbon Bainitic Steels and High Manganese Twinning-Induced Plasticity Steels". Thesis, 2018. http://ndltd.ncl.edu.tw/handle/a4y5w6.
Texto completo國立臺灣大學
材料科學與工程學研究所
106
Low carbon steels have been wildly used in line pipes, the automotive industry, and submarine environments due to their remarkable mechanical properties, weldability and formability. In the 2000s, micro-alloying elements were added into low carbon steels to further enhance the performance and meet increasing demand. In the present study, the performance of low carbon steels and TWIP steels is enhanced by the addition at least two strong carbide forming elements, appropriate heat treatment and microstructure control. The effects of Nb accompanied with other strong carbide forming elements in BCC and FCC matrix are investigated through microstructural observations with optical microscopy, scanning electron microscopy, transmission electron microscopy, and mechanical property tests. The relationships between mechanical properties and microstructure are clearly illustrated in this study. Chapter 4 presents an efficient and accurate method for microstructural quantification of complex phases in a low carbon Nb-Mo bearing steel. Optical micrographs showed that this steel consisted of granular bainite with a small amount of ferrite and degenerated pearlite. In our previous work, we proposed a method to measure the misorientation angles via electron backscatter diffraction (EBSD) so as to differentiate granular bainite and ferrite. That method is accurate for phase quantification but laborious for the characterization process. To resolve this difficulty, in this study, EBSD was used in combination with a kernel average misorientation (KAM) map for phase characterization. Comparisons were made among KAM maps with different kernel sizes (300 to 600 nm) and various step sizes (100 to 600 nm). It is found that a kernel size close to the sub-structure size of granular bainite (500 nm) is optimal for phase identification, while varied step sizes produce relatively invariant results. Therefore, KAM maps can be used for fast and reliable phase quantification, provided that an appropriate kernel size and a large step size are used. Chapter 5 describes an investigation of the effects of tempering at three high temperatures (660, 680 and 700 ºC) for different holding times (5 min to 16 h) on the secondary hardening in Nb-bearing and Nb-Mo-bearing bainitic steel strips. It is found that with 0.3 wt.% Mo addition in Nb-Mo-bearing bainitic steel strip, the peak hardening occurs with a significant increment in hardness (up to 40 Hv) after approximately 10 min of tempering at all temperatures (660, 680 and 700 ºC). In contrast, for the Nb-bearing steel strip, the corresponding increment in hardness is small (about 15 Hv). Investigations of the microstructural evolutions of Nb-bearing and Nb-Mo-bearing steel strips during tempering at 700 ºC are also presented. It is found that during tempering, bainitic ferrite platelets in Nb-Mo-bearing steel strips remain much more stable and have a higher dislocation density than those in Nb-bearing steel strips. High-resolution transmission electron microscopy provides strong evidence that the Mo addition has significant effects on suppressing the annihilation rate of dislocations and retarding the coarsening rate of nanometer-size carbide particles at higher temperatures, leading to a remarkable resistance to softening after secondary hardening. In chapter 6, the microstructure evolution and mechanical properties of twinning-induced plasticity (TWIP) steel subjected to high temperature aging are elucidated. The yield stress and ultimate tensile stress of 18Mn-0.4C TWIP steel respectively increase by 46 MPa and 146 MPa after 700 ºC aging. Microstructural characterizations conducted to clarify the increments in strength are also presented. The as-received TWIP steel contained dense and homogeneously distributed dislocations, which, after aging, rearranged themselves into a lath-like sub-structure without obvious annihilation. In addition, the number density of precipitates was higher in the aging than in the as-received TWIP steel sheet. Ductile fracture surfaces were found both in the aging and as-received TWIP steel, and the deformation structures were investigated using transmission electron microscopy. In the as-received TWIP steel, austenite grains were dominated by single-variant primary mechanical twins, and few secondary twins were found. On the other hand, in the aging TWIP steels, a high amount of multiple-variant nano-sized mechanical twins with some strain-induced α’ martensite in the intersections was found. It is appropriate to conclude that after aging, the presence of a high amount of precipitates retards the formation of deformation twins, causing premature saturation of single-variant mechanical twins. Therefore, more secondary mechanical twins are activated, and they in turn interact with the primary twins as strain increases, inducing α’ martensite formation in the intersection. This phenomenon increases the strain hardening rate at a late stage (εe = 0.41) and thus the ultimate tensile stress in the aging TWIP steel.
Yin-HsiangMao y 毛胤翔. "Titanium Addition of Niobium Nitride Single and Multilayer Coating on Wear Property, Corrosion Resistance and Applications on High Speed Drills after Acetylene Introduction". Thesis, 2019. http://ndltd.ncl.edu.tw/handle/2vvdbb.
Texto completo國立成功大學
機械工程學系
107
This study was composed of three stages. In first stage, NbNxA coatings were prepared by DC magnetron sputtering. In second stage, NbTi-NX and NbN/TiNxmin coatings were prepared using RF magnetron sputtering. In third stage, acetylene was introduced to prepare NbTi-NX-CH coating. Considering wear property and corrosion resistance, NbTi-N12-CH coating was the optimal parameter for preparation in this research. Applied the NbTi-N12-CH coating to a high-speed drill and tested it by drilling 2000, 4000, and 6000 holes. The results revealed that applying this coating to the drill could increase its drill life to 4000 holes, which is two times longer than that of an uncoated drill.