Rozprawy doktorskie na temat „Aluminum pin”

Friction StirWelding (FSW) has been researched for a number of years since its inception in 1991. The work thus far has been based on understanding the material and thermal flow using the standard fixed pin tool. The keyhole resulting during tool extraction in a FSW weld, is a disadvantage and a current limiting factor. Eliminating this effect from a weld using a movable pin tools would make FSW more commercially viable. This dissertation focuses on the design of a novel retractable pin tool, and highlights the problems encountered during the welding of Aluminum plates, Al2024 and Al5083. Previously studied techniques of material and thermal flow were used, to investigate the effect of the tool during extraction in a FSW weld. A prototype retractable tool was designed using parametric and axiomatic design theory, and implementing a pneumatic muscle actuation system. The resulting problems in the calibration of the retractable pin tool and the resulting welds are presented, these results confirming previous studies. The movable pin produced discrepancies the heat generation around the shoulder during a FSW weld. The failure of this tool to produce a reasonable weld showed that previous ideas into the workings of a retractable pin tool requires further investigation, furthermore a fresh approach to the interpretation and understanding of the FSW weld process needs consideration.

Aluminum and aluminum-alumina powder mixtures were used to produce pyramidal fin arrays on aluminum substrates using cold spray as an additive manufacturing process. Using aluminum-alumina mixtures instead of pure aluminum powder could be seen as a cost-effective measure, preventing nozzle clogging. The fin geometries that were produced were observed using a 3D digital microscope to determine the flow passages width and fins geometric details. Heat transfer and pressure tests were carried out using different ranges of appropriate Reynolds numbers for the sought commercial application to compare each fin array and determine the effect of alumina content. It was found that the presence of alumina reduces the fins’ performance when compared to pure aluminum but that they still outperform traditional fins. Numerical simulations were performed and were used to explain the obtained experimental results. The numerical model opens up new avenues in predicting different parameters such as pressure and substrate temperature.

Aircraft are often designed with numbers determined by testing in a lab, rather than by repeatedly building prototypes. These lab tests conform to testing specifications so that the numbers can be compared between manufacturers, suppliers, and lab technicians. One such specification is ASTM specification E238 – 84(08), and it is used to determine important properties of a bearing pin joint like hinges, bolt holes, and rivet joints. The properties determined from this fastener-through-plate method are bearing strength, bearing yield strength, and bearing stiffness. Adhering to the methods outlined in ASTM E238, a study was performed, looking at the effects that plate material, fastener used, fastener lubrication, and plate hole preparation method (whether drilled and reamed or just drilled) have on the three bearing joint properties. The plate materials used were Al 7050 – T7451, Ti – 6Al – 4V (mill annealed), and PH13 – 8Mo – H1000. The fasteners were Ti – 6Al – 4V screws, coated A286 screws, and high speed steel (HSS) pins used as a control. Lubrication was tested using a corrosion inhibitor, PR – 1776M B – 2 from PRC – DeSoto, on the fastener or leaving the fastener uncoated. The HSS pins were always tested in the uncoated condition. 54 runs were performed, as outlined by a D-optimal design of experiment. It was discovered from the statistical analysis of the results via ANOVA that both the plate material used and the pin material, whether a screw or a pin, had a significant effect on the bearing strength, bearing yield strength, and bearing stiffness. The interaction between the two factors was also significant on all responses but the bearing stiffness. PH13 – 8Mo – H1000 plates seemed to perform best on average, followed by Ti – 6Al – 4V plates, then Al 7050 – T7451 plates. PH13 – 8Mo – H1000 and Ti – 6Al – 4V plates had similar bearing strength and bearing yield strength averages with the HSS control pins being used, which had the highest mean values for a given plate and fastener. The Ti – 6Al – 4V and A286 screws behaved and performed statistically similar in most cases, except when hole preparation method was take into account. The Ti – 6Al – 4V screws performed better when the hole was drilled and reamed, while the coated A286 screws performed better when the hole was drilled only. All screws had lower resulting bearing properties than the HSS control pins. It was also found that ASTM specification E238 – 84(08) is a precise test method, since the method could be performed repeatably and reliably with no missing data points. Therefore, this ASTM testing method is reasonable for determining bearing properties, which can then be used to design aircraft.

En Europe, les forêts de résineux sont très répandues et connues pour modifier les caractéristiques physicochimiques des sols forestiers, essentiellement en termes d’acidité. A des pH inférieurs à 5,5, l’aluminium naturellement présent dans le sol est solubilisé et se retrouve sous une forme mobile (Al3+),biodisponible et par conséquent toxique pour les plantes. Les travaux menés ont porté plus particulièrement sur le sapin de Douglas (Pseudotsuga menziesii), un conifère largement répandu en France et particulièrement dans la région Limousin. Plusieurs conditions de culture différentes (conditions contrôlées in vitro et conditions semi contrôlées sous serre sur sols forestiers acides et riches en Al potentiellement phytodisponible), ont été utilisées pour étudier, à des stades de développement différents (stade plantules et stade jeunes arbres) et pour des périodes d’exposition différentes (2 et 11 mois) les réponses du sapin de Douglas suite à son exposition à l’Al. Les résultats ont montré que la croissance du sapin de Douglas et sa nutrition minérale sont perturbées quand les plantules sont exposées à des concentrations élevées en Al (500 μM AlCl3 in vitro ; environ 1 mg Al.g-1 sol sec avec des pH d’environ 5 sur sols forestiers). Les symptômes de toxicité concernent essentiellement les racines qui accumulent la majorité de l’Al absorbé par la plante, l’aluminium étant préférentiellement localisé dans les parois cellulaires des tissus de la pointe racinaire. Face à la toxicitéaluminique, le sapin de Douglas développe différentes stratégies. D’une part, la caractérisation chimique de la paroi cellulaire a mis en évidence des modifications quantitatives et qualitatives dans la composition polysaccharidique de la paroi notamment en pectines (plus riches en acides alacturonique et moins ramifiées) suite à une régulation de l’activité pectine méthylestérase, et en hémicelluloses (plus riches en glucomannanes), suggérant un processus de rétention de l’Al dans les structures pariétales. D’autre part, au niveau intracellulaire, les résultats ont montré une stimulation de l’activité guaïacol peroxydase, une enzyme clé dans la réduction des symptômes du stress oxydatif induit dans des conditions de stress aluminique ainsi qu’une accumulation de la proline, potentiellement capable de chélater l’Al à l’intérieur de la cellule. Ainsi, le sapin de Douglas présente un seuil de tolérance à l’Al relativement élevé comparable à celui d’autres conifères. Cette tolérance met en jeu une stratégie à l’échelle cellulaire basée à la fois sur l’exclusion au niveau pariétal mais aussi de façon complémentaire sur des mécanismes de chélation au niveau intracellulaire
In Europe, softwood forests are very abundant and are characterized by an acidic soil profile. In these conditions, when the soil pH drops below 5.5, aluminum is present in soils in a soluble and bioavailable form Al3+. This work was carried out on Douglas fir (Pseudotsuga menziesii), a coniferous tree, widely distributed in France and particularly in the Limousin region. In this study we used different cultivation methods (in vitro cultures with controlled conditions, and semi-controlled conditions in greenhouse on naturally acidic forest soils rich in Al). Plants were analyzed at different stages of development (seedling stage and young tree stage) and for different exposure periods (2 and 11 months). The results have shown that the growth of Douglas fir and its mineral nutrition were disturbed when exposed to high Al concentrations (500 μM AlCl3 in vitro, and about 1 mg Al.g-1 at pH 5 on forest soils). We showed that the roots exhibited severe symptoms of toxicity and accumulated the majority of the Al within the cell wall. It has been shown that, to cope with aluminum toxicity, Douglas fir developed different strategies. On one hand, the chemical characterization of the cell wall revealed quantitative and qualitative modifications in the polysaccharidic composition of the wall, in particular pectins (harboring a higher galacturonic acid content with less ramification) following regulation of pectin methylesterase activity, and hemicelluloses (richer in glucomannans), suggesting a trapping process of Al in the cell wall structures. On the other hand, at the intracellular level, the results showed a stimulation of a key enzyme activity involved in the reduction of oxidative stress induced under aluminum stress, as well as an accumulation of proline, potentially capable of chelating Al inside the cell. Therefore, Douglas fir plantlets showed a relative high tolerance level to Al equivalent to other coniferous species which can be explained at the cellular level by an exclusion process involving retention by the cell wall but also a complexation process in the intracellular compartment

O desgaste é responsável por um grande número de falhas em materiais, provocando a sua substituição antecipada e consequentemente diminuindo a sua vida útil. Por isso, estudos são realizados para caracterizar os limites de utilização desses materiais, evitando assim situações catastróficas. A partir das variáveis e parâmetros envolvidos no ensaio de desgaste, é possível construir mapas que tem como finalidade direcionar para uma correta escolha do material, de acordo com a aplicação desejada, além de identificar o seu comportamento frente à determinadas condições de uso. Neste contexto, este trabalho teve como objetivo conhecer o comportamento de desgaste de nanocompósitos de alumina contendo 5% de inclusões nanométricas de zircônia, visando construir um diagrama de transição de desgaste entre os limites de combinação de velocidade de deslizamento e carga aplicada. Para isso, corpos de prova conformados na forma de pinos com uma das extremidades semiesféricas foram caracterizados quanto a dureza e tenacidade à fratura, submetidos ao ensaio de desgaste do tipo pino-no-disco com temperaturas e umidades ambientes, variando os parâmetros de velocidade e carga. As velocidades de deslizamento variaram de 1,2 m/s à 0,1 m/s e as cargas variaram de 2 N à 100 N. Os valores de dureza e tenacidade a fratura obtidos foram de 14,08 ± 1,22 GPa e 3,99 ± 0,14 MPa.m1/2, respectivamente. Os resultados de desgaste mostraram que a partir da caracterização e construção do diagrama de transição de regime de desgaste, com combinações de parâmetros extrínsecos de carga e velocidade de deslizamento, foi possível definir e atingir as condições limites entre o regime de desgaste moderado e a transição para o regime severo. Esse diagrama auxilia na seleção e comparação da transição entre os limites de desgaste do material estudado com outros tipos usados na engenharia.
Wear is responsible for a large number of material failures, causing them to be replaced early and consequently shortening their life-time. Therefore, studies are conducted to characterize the limits of use of these materials, thus avoiding catastrophic situations. From the variables and parameters involved in the wear test, it is possible to construct maps that aim to direct the correct choice of material according to the desired application, as well as to identify its behavior against certain conditions of use. In this context, the objective of this work was to know the wear behavior of alumina nanocomposites containing 5% nanometric zirconia inclusions in order to construct a simplified wear transition diagram between the sliding speed and applied load combination limits. For this, test pieces shaped like pins with semi-spherical tips were characterized in terms of hardness and fracture toughness, took to the wear test of the pin-on-disk with ambient temperatures and humidity, varying the speed and load parameters. Slip velocities ranged from 1.2 m/s to 0.1 m/s and loads ranged from 2 N to 100 N. The values of hardness and fracture toughness obtained were 14.08 ± 1.22 GPa and 3.99 ± 0.14 MPa.m1/2, respectively. The results of wear showed that from the characterization and construction of the wear regime transition diagram, with combinations of extrinsic load parameters and slip speed, it was possible to define and reach the boundary conditions between the moderate wear regime and the transition for the severe regime. This diagram helps in the selection and comparison of the transition between the wear limits of the studied material with other types used in engineering.

To reduce CO2 emissions the cement industry has for decades diluted the Portland cement fraction of concrete binders with Supplementary Cementitious Materials (SCM). Defining the reactivity of these aluminosilicate-based materials and their interaction with clinker phases has however challenged the research community and limited their replacement levels. In the present study, to quantify the reactivity of SCMs during early hydration, aluminosilicate glasses with compositions representative of blast furnace slag and fly ash systems were synthesised and exposed to different activator solutions in a continuously stirred closed system reactor for a period up to 3 h. Solution compositions were measured from the very first minutes of dissolution with complementary solid surface analysis. The experimental conditions were designed to avoid precipitation, however an initial Ca maximum in the first 30 min of exposure to the activating solution was a common feature in most dissolution profiles with a subsequent rapid decline, most likely attributable to Ca-reincorporation on the reacting surface. Surface specific analysis confirmed Ca enrichment on the surface and also detected Al enrichment, suggesting the formation of a Ca-modified aluminosilicate phase by a dissolution reprecipitation mechanism on the surface of the glass. Differing chemistries are thought to be responsible for the Ca and Al re-integration on the reacting surface depending on the pH of the solution; near-neutral conditions favour Ca-readsorption and surface condensation reactions, whereas alkaline solutions favour Ca-reintegration via covalently bound phases. The Ca concentration in solution was also observed to control glass alteration. Decreased dissolution rates were in fact observed as Ca concentrations in solution were increased supporting the formation of a C-A-S-H phase on the surface, the formation of which was instead suppressed when a Ca chelating chelating agent (EDTA) was added to the solution resulting in increased glass dissolution. Experiments using in situ AFM and LAOICPOMS are also reported and the significance of the findings to the early hydration reactions of a blended cement system is discussed.

Wear and biological response to wear debrisof artificial joints remain the major concerns in total hip arthroplasty (THA) [1].Silicon carbide reinforced alumina, Al2O3-SiCw,can be considered as a candidate for hip implants due to its high hardnessand toughness, aswell as chemical inertness. In this study, thewear and friction properties of Al2O3-SiCw areinvestigated by pin-on-disc experiments, with Hank’s Buffered Salt Solution(HBSS) as lubricant. Comparisons with BIOLOX®delta,the most commonly used ceramic in THA, under the same test conditions are made as well.

The general aim of this thesis was to investigate the mechanisms that determine variation in Al accumulation among tropical woody plants. The focus of the study variation among populations of the well-studied Al accumulator Melastoma malabathricum, but this was coupled with sampling 50 tree species growing on the 50 ha forest dynamics plot at Pasoh Forest Reserve in Peninsular Malaysia in order to gain a perspective on Al accumulation at a community scale. I sampled mature leaves and seeds of M. malabathricum from 20 populations growing in six habitats across Peninsular Malaysia. Concentrations of Al, N, P, K, Ca and Mg were determined in air-dried leaves and the soil from each site. The seeds were used to generate cohorts of seedlings that were grown in hydroponic solutions amended with Al in the form of 1.0 mM AlCl3. Foliar Al concentrations varied significantly among populations, but were not consistently different among plants growing in different habitats and showed no relationship to total or exchangeable Al concentrations in soils collected at the 20 sites. Similarly, foliar Al concentrations in seedlings grown in the presence of Al differed significantly among source populations, but values did not correlate with foliar Al concentrations in wild plants from parent populations. Mean foliar Al concentration in wild plants was positively correlated with foliar Ca concentration, and with total soil Ca and Mg concentrations, across the 20 populations. Furthermore, total dry mass and relative growth rates were significantly greater for seedlings that had received Al in the growth medium than for seedlings that had received no Al. The growth response to Al addition varied among populations of M. malabathricum, and relative growth rate in response to Al addition was greater for populations that accumulated higher foliar Al concentrations. In a further experiment, increasing Al concentrations from In a further experiment, increasing Al concentrations from 0 to 2.0 mM in the nutrient solution increased rates of growth, but growth declined at 5.0 mM Al. The responses to Al addition varied among populations for growth, photosynthesis, respiration, carbon allocation, and foliar P, Ca, and Mg concentrations. The rates of photosynthesis and respiration, and total nonstructural carbohydrate concentrations, were higher for seedlings grown in the presence of 2.0 mM Al in the nutrient solution than in the absence of Al, while lignin concentration in roots decreased. These results suggest that Al addition stimulate growth stimulation by increasing rates of photosynthesis and respiration, resulting in higher non-structural carbohydrate concentrations. Increased allocation of photosynthate to root systems coupled with their lower lignification results in enhanced nutrient uptake (particularly P, Ca and Mg), which contributes to enhanced whole-plant growth. To test the prevalence of Al accumulation at the community scale I sampled 50 tree species growing on the 50 ha Forest Dynamics Plot at Pasoh Forest Reserve in Peninsular Malaysia. Twenty two species possessed foliar Al concentrations that exceeded a value of 2.3 mg g-1 Al dry mass, which is a suitable threshold for detecting Al accumulators in Southeast Asian forests. A phylogenetic signal was detected for foliar concentrations of Al and other elements, suggesting that more closely related species have more similar values of these traits. A canonical correspondence analysis (CCA) revealed that soil Al concentrations have limited influence on the fine-scale distribution of the tree species sampled at Pasoh. I conclude that the distribution of differences in the expression of Al accumulation among populations of M. malabathricum and the distribution of Al accumulator species within a tree community growing at one site are uncoupled from soil Al concentrations, but may be linked to other soil properties such as Ca and Mg concentrations. When supplied in nutrient solutions, Al promotes the growth of the Al accumulator M. malabathricum through a physiological mechanism that includes up-regulation of photosynthetic and respiration rates. The functional significance of this growth response for plants growing under natural conditions in the field requires further investigation.

The dehydroxylation process of pseudo-boehmite to yield acidic amorphous silica-alumina has been investigated by increasing the temperature of the sample and recording DRIFTS spectra of its surface and monitoring the water released with an on-line mass spectrometer. The Brønsted and Lewis acid sites density of amorphous silica-alumina has been determined by IR-spectrometry of adsorbed pyridine and using molar extinction coefficients specific for this system for silica-alumina samples calcined at different temperatures. The deactivation profiles of 1-butene isomerisation (double-bond migration) over amorphous silica-alumina samples calcined at different temperatures have been acquired by using a fixed bed laboratory reactor coupled to a gas chromatograph with an automated sampling valve. The initial activities of amorphous silica-alumina calcined at different temperatures correlated with the Brønsted acid site density of the samples. The deactivation profiles are consistent with a reversible rehydration deactivation mechanism involving both Brønsted and Lewis acid sites and simultaneous to an irreversible deactivation mechanism involving Lewis acid sites. Brønsted acid sites are considered to be the active sites of the reaction, whereas part of the Lewis acid sites is converted into Brønsted acid sites by rehydration.

I used a data-set of 986 plant species (from 493 genera in 195 families) obtained from a literature search and a new data collection for 58 tropical tree species (from 31 genera in 18 families) growing in two contrasting forest types in Brunei Darussalam: mixed dipterocarp forest on moderately infertile ultisols and fluvisols, and heath forest on acidic and nutrient-poor spodosols.  I provide statistical evidence for the existence of discreet groups of species representing Al accumulators and non-Al accumulator based on foliar Al concentrations.  The threshold foliar Al concentration was higher for tropical plants (range 2.3-3.9 mg Al g^-1) than temperate plant (1.1 mg Al g^-1). Species’ mean log foliar Al concentration was also higher for tropical (0.73 ± 1.11 mg Al g^-1) than temperate plants (0.16 ± 1.07 mg Al g^-1).  I used the tropical Al accumulating shrub Melastoma malabathricum L. as a study species to test the hypotheses that growth would be stimulated by Al addition.  Growth of M. malabathricum seedlings was stimulated by Al addition when the external supply of macronutrients was very low, and this growth response was associated with an increase in net assimilation rate and specific leaf area.  Foliar Al concentration was positively correlated with foliar concentrations of Ca and Mg across 16 Al accumulator species sampled in the field study in Brunei Darussalam, while foliar Al and K concentrations were correlated positively in M. malabathricum seedlings growing in the solution culture experiments.  These positive correlations contradict the hypothesis that Al inhibits the uptake of nutrient cations and they may contribute to the positive growth response to Al addition in Al accumulator plants.

Mestrado em Engenharia do Ambiente - Instituto Superior de Agronomia
Given the growing food requirements, mainly due to the increase of the world population, the global livestock sector is more intensive. The pig production, an important sector follows this trend yielding large quantities of slurry, rich in nutrients, organic matter and higher amount of metals in the livestock effluents. Physico-chemical processes procedures are effective in the treatment of effluents, which includes coagulation / flocculation. This tecnhology was selected for the development of an experimental study on a raw effluent to simulate reality, where the nutrient removals were analyzed by coagulation / flocculation. In this study the effectiveness of conventional coagulants and polymers was compared, after optimization of the dose, agitation time and speed and volume of sludge produced. The biopolymer used was chitosan, because it is abundant and natural. Aluminum sulphate (Al2(SO4)3) was found to be more effective than ferric chloride (FeCl3), two of the most commonly used coagulant in the treatment of waste water. Comparing the results with the ones obtained by natural sedimentation, it is shown that the coagulation / flocculation is effective in removing turbidity and COD, and especially in the removal of metals analyzed. These removals exceed 60% and reduce the sludge volume by about 38%. The phosphorus, element which can cause eutrophization of the water is removed almost entirely (around 70%-94%).

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Dissertacao (Mestrado Profissionalizante em Lasers em Odontologia)
IPEN/D-MPLO
Instituto de Pesquisas Energeticas e Nucleares, IPEN/CNEN-SP; Faculdade de Odontologia, Universidade de Sao Paulo

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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

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Dissertacao (Mestrado Profissionalizante em Lasers em Odontologia)
IPEN/D-MPLO
Intituto de Pesquisas Energeticas e Nucleares, IPEN/CNEN-SP; Faculdade de Odontologia, Universidade de Sao Paulo

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Os aços de ultra alta resistência como o aço 4340 tem sido amplamente utilizados pela indústria aeronáutica e aeroespacial em aplicações como trens de pouso de aeronaves e o veículo lançador de satélite brasileiro (VLS), além de um uso extensivo para diversos setores da indústria em geral. Isso se deve, em grande medida, às suas propriedades mecânicas. Este trabalho se propõe a avaliar as propriedades tribológicas do par aço 4340, inicialmente submetido ao tratamento térmico de têmpera e revenimento, e a liga bronze alumínio 630, utilizados em trens de pouso. Será estudado o comportamento destas estruturas após o aço ser submetido a tratamentos de superfície por nitretação a plasma e carbonetação a laser, como forma de melhorar seu desempenho com relação ao atrito e ao desgaste. Neste estudo foi escolhido o ensaio tipo pino-disco para simular a situação real de desgaste. Os discos foram confeccionados a partir do aço AISI/SAE 4340 e os pinos foram feitos da liga bronze-alumínio 630. Foram realizadas análises microestruturais das estruturas e das camadas de compostos formadas devido ao tratamento de superfície, Após os ensaios de desgaste foram feitas observações das superfícies através de microscopia e perfilometria óptica, microscopia eletrônica de varredura, difratometria de raios-X, testes de riscamento (scratching tests), dureza, observação de rugosidade e pesagem dos corpos de prova. Foram levantados os parâmetros do desgaste e alterações microestuturais devido à interação entre as superfícies de contato durante os ensaios de deslizamento. Foi analisada a perda de massa e levantadas as curvas de desgaste e dos parâmetros relacionados ao atrito em função da distância percorrida e/ou do tempo de ensaio. Nos ensaios foram utilizadas três velocidades de ensaio: 0,5; 1,0 e 1,5 m/s. Foi possível o cálculo da taxa de desgaste para cada par e velocidades estudadas. De uma maneira geral constatou-se que os mecanismos de desgaste detectados são semelhantes para todas as condições de superfície dos discos. As imagens mostram que partículas do pino são deformadas sobre o disco, em forma de camadas, evidenciando o mecanismo de adesão. A carbonetação a laser criou uma camada rica em carbono com a presença de grafite que contribuiu para reduzir o coeficiente de atrito e o desgaste do pino, principalmente, para as velocidades de 0,5 e 1,0 m/s. A nitretação a plasma reduziu a perda de massa do disco e do pino, com indicativos de pequena perda de massa para todas as velocidades estudadas; a rugosidade e o aumento do coeficiente de atrito no par pino-disco para as velocidades de 1,0 e 1,5 m/s podem ter sido induzidas por alteração no tipo de desgaste, de adesivo para uma abrasão a três corpos.
Ultra high strength steels as 4340 steel has been widely used by the aerospace industry in applications such as aircraft landing gears and the Brazilian satellite launch vehicle (VLS), plus an extensive use for various sectors of the industry in general. This is due largely to their mechanical properties. This work aims to evaluate the tribological properties of 4340 steel pair, initially submitted to heat treatment of quenching and tempering, and aluminum bronze 630 alloy, used in landing gear. The behavior of these structures after the steel be subjected to surface treatment by plasma nitriding and laser carbonetation will be studied, as a way to improve its performance with respect to friction and wear. For this study, pin-on-disc test was chosen in order to simulate the real situation of wear. The discs were made from 4340 steel and pins were made of aluminium bronze 630 alloy. Micro-structural analyses were undertaken of the structures and compound layers formed due to surface treatment. After the wear tests surface observations were made through microscopy and perfilometry optical, scanning electron microscopy, x-ray diffractometry, x-ray tests, scratching tests, hardness, roughness and weighing of the specimens. Parameters of wear and microestuturals changes were raised due to interaction between the contact surfaces during rehearsals. Loss of mass was analyzed and curves of wear and friction related parameters were plotted in function of the slided distance and/or time of test. In the tests three test velocities were used: 0.5; 1.0 and 1.5 m/s. It was possible to calculate the wear rate for each pair and studied velocities. In general it was noted that the mechanisms of wear detected are similar for all conditions of the surface of the discs. The images show that the particles are bent on the disc, in the form of layers, showing the mechanism of adhesion. The laser carbonetation created a carbon-rich layer with the presence of graphite, which contributed to reduce the friction coefficient and pin wear, mainly for the 0.5 and 1.0 m/s velocities. The plasma nitriding reduced the loss in mass of the disk and pin, with indicative of small mass loss for all velocities studied; the roughness and the increase of the coefficient of friction in the couple pin-disc for the velocities of 1.0 and 1.5 m/s may have been induced by changes in the type of wear, from adhesive wear to a three-body abrasion.
CAPES: 99999.002441/2014-04

Durant l'orogène du "Pan-Africain" (~ 600 Ma), la région du Hoggar central, à l'instar de l'ensemble du Bouclier Touareg, a été intensément affectée. Cet évènement est accompagné de la mise en place d'ensembles magmatiques variés. Dans la région de Tamanrasset, deux magmatismes de nature différente sont mis en évidence : magmatisme subalcalin et magmatisme alumineux. Le premier est représenté par les massifs syn à tardi-orogéniques (Anfeg - Tifferkit), voire post-orogénique (Aheleheg') tandis que le second est exclusivement constitué par les plutons post-orogéniques (In-Tounine et intrusions granitiques à albite-topaze). Compte tenu des critères de terrain, pétrographiques, géochimiques et parfois isotopiques, trois groupes magmatiques peuvent être distingués.

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Universidade Federal de Sao Carlos
Searching for wear resistant materials, attention has been paid to Si3N4, SiC, Al2O3 and ZrO2 ceramics due to their better properties as compared to other materials. Although ceramic are brittleness, improvements on the processing and by the addition of second phases to the ceramic matrix have lessen this restriction because of microstructure refinement. Therefore, some mechanical proprieties have been optimized e probably the wear resistance also. Among the ceramic composites, greater attention has been given to the alumina nanocomposites due to the improvements on the toughness, hardness and mechanical resistance. Wear research has been made in the literature but, a direct comparison between the many published works regarding this wear improvement is impossible due to the fact that wear resistance is a response of the microstructure, material and testing condition. So the work herein presented aim was to do a systematic study in the alumina wear based on the critical parameters which have to be controlled on a pin-on-disc test concerning about the mild and severe wear regime. Since, it was possible to describe a procedure to evaluate the alumina wear behavior and resistance in terms of applied load, sliding speed and environment. By the use of the study methodology proposed, it was possible to construct a simplify wear transition diagram which allowed to define parameters combination were alumina can be use as a wear resistance material
Na busca por materiais resistente ao desgaste, atenção tem sido dada a cerâmicas como Si3N4, SiC, Al2O3 e ZrO2, por apresentarem melhores características quando comparadas com outros materiais. Apesar da fragilidade destas cerâmicas, pelo melhoramento no processamento e pela introdução de segundas fases nas matrizes cerâmicas, algumas propriedades mecânicas como a de resistência mecânica foram melhoradas pelo refino microestrutural e provavelmente, a resistência ao desgaste. Dentre os compósitos cerâmicos, grande atenção tem sido dada aos nanocompósitos de matriz de alumina pelos seus resultados excepcionais quanto à tenacidade, a resistência mecânica e a dureza. Alguns estudos de resistência ao desgaste destas cerâmicas densas têm sido feito, porém a comparação dos resultados obtidos é difícil, pois a resistência ao desgaste é uma resposta da microestrutura, do material e das condições dos testes. Visando compreender os parâmetros que afetam o valor de desgaste e melhorar a reprodutibilidade dos resultados de desgaste em cerâmicas densas, o objetivo proposto para a presente dissertação foi o estudo sistemático do desgaste da alumina frente às questões dos parâmetros críticos que devem ser controlados em um ensaio de desgaste do tipo pino no disco. Foram verificadas as condições de ensaio que influenciam a determinação dos parâmetros críticos, entre as condições de desgaste moderado e severo. Dessa, forma, foi possível descrever um procedimento para avaliar a resistência e o comportamento de desgaste de alumina quanto aos parâmetros de ensaios de velocidade de deslizamento, carga aplicada e umidade relativa do ar. Esta metodologia permitiu a construção de um diagrama de transição de desgaste simplificado que possibilitou a definição de limites de combinações destes parâmetros que permitem obter bom desempenho da alumina em situações que necessitem de resistência ao desgaste

Sélectionner des traitements de surface pour l’industrie nécessite de prendre en compte :les propriétés à conférer au substrat, la nature et la géométrie de celui-ci et les caractéristiques du milieu extérieur. Certaines combinaisons de ces paramètres rendent difficile la sélection d’un traitement unique, d’où le recours à des multitraitements de surface. Dès lors, se posent les questions suivantes :

- Utiliser des multitraitements de surface peut se faire en scindant les différentes requêtes en sous-ensembles, de manière à ce que chaque traitement réponde à l’un d’eux. Dans quel ordre ces requêtes doivent-elles être introduites par rapport au substrat ?

- Comment sélectionner les traitements de surface répondant à chaque requête individuelle ?

- Comment classer des multitraitements en termes d’adéquation au problème posé ?

Dans ce travail, les première et troisième questions sont abordées, en explorant les requêtes concernant habituellement les dispositifs de moulage de l’aluminium :

- Résistance aux contraintes d’origine thermique.

- Résistance à la corrosion par les métaux fondus.

- Résistance au frottement.

L’analyse de la bibliographie relative aux traitements de surface utilisés dans ces systèmes a été analysée et des « architectures »-types ont été identifiées (chapitre 3). On prévoit, par exemple, un traitement conférant la résistance à la fatigue superficielle, ainsi qu’un revêtement étanche et résistant à l’aluminium fondu. Une barrière thermique est parfois préconisée.

Pour chacune des architectures, des traitements de surface individuels peuvent être sélectionnés. Un « facteur de performance » permettant de classer les solutions par rapport au problème de la fatigue thermique a été construit (chapitre 4) et discuté dans deux situations :

- Lorsqu’un revêtement est présent, et que les contraintes d’origine thermique (différence de dilatation thermique couche-substrat) menacent de le rompre lors de l’immersion dans un milieu corrosif à haute température. Des essais de corrosion dans de l’aluminium fondu ont été réalisés sur un acier revêtu par du nitrure de chrome dopé à l’aluminium, synthétisé par déposition physique en phase vapeur (chapitre 5 – collaboration :Inasmet).

- Lorsque des variations thermiques rapides menacent de rompre le substrat et la (les) couches. Des essais de fatigue thermique ont été réalisés sur de l’acier à outils pour travail à chaud non traité, boruré ou recouvert d’un multitraitements (zircone yttriée / NiCrAlY / boruration / acier). Le revêtement en zircone yttriée a été obtenu par projection par plasma. L’essai de fatigue thermique a été modélisé et le facteur de performance, discuté (chapitre 6).

Au chapitre 7, les architectures-types ont été introduites dans une méthodologie de sélection des multi-traitements de surface, qui a été appliquée dans deux cas :

- Celui des moules de fonderie, devant résister à la fatigue thermique et à la corrosion par l’aluminium fondu. Le facteur de performance a été extrapolé à d’autres situations qu’aux chapitres 5 et 6. Les solutions habituellement proposées pour résoudre ce problème sont retrouvées.

- Celui de deux pièces en acier frottant l’une contre l’autre en présence d’aluminium fondu.

To select surface treatments, one must account for the required functional properties, the substrate features and the solicitations the substrate must endure. Certain combinations of these parameters make it difficult to select a single surface treatment, a reason why several successive treatments are preferred. To select them, one needs to determine:

- How to divide the several requests into groups and how to stack up these groups from the substrate to the outer surface, so that each treatment deals with one specific group of requests/properties.

- How to select individual layers for each group of properties.

- How to rank the multi-treatments in terms of relevance for a given application.

In this work, one tries to answer the first and the third questions, by studying the case of aluminium foundry, in which the industrial devices frequently face the following solicitations:

- Thermal stress (thermal fatigue, thermal expansion mismatch).

- Presence of corrosive molten metal.

- Sliding wear.

In the literature, several “standard” architectures are proposed (chapter 3), like a diffusion layer reducing superficial fatigue plus a corrosion barrier layer. A thermal barrier coating is also sometimes proposed.

For each of these architectures, one can select individual treatments. To rank them, one devised a “performance index” for thermal stress (chap.4), which is discussed for two cases:

- For large differences between layer and substrate thermal expansion coefficients, when both are put into contact with a high temperature corrosive medium, the layer may be damaged. One discusses this case by examining the corrosion caused by molten aluminium for a steel substrate coated by anticorrosive chromium nitride doped with aluminium. The layer is produced by physical vapour deposition (chap. 5 – cooperation: Inasmet).

- Repeated fast surface temperature transients can also damage the substrate and/or the layer by thermal fatigue. One conducted thermal fatigue tests with samples of hot work tool steel, respectively untreated, simply borided and protected by a multilayer. In the last case, top coat is yttria stabilised zirconia, followed by a nickel superalloy and then a borided layer (undercoat). One synthesized the zirconia coating by plasma spray and one modelled the thermal fatigue (chap. 6).

In chap. 7, architectures from chap. 2 are introduced in a multi-treatment selection routine, which is applied in two cases:

- Foundry moulds for molten aluminium, withstanding both thermal fatigue and corrosion. The devised performance index is extrapolated beyond the tests of chap. 5 and 6 to treatments for this industrial application, thereby quantifying their respective merits.

- A foundry device exposed to molten metal and sliding wear.

Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished

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CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Recentemente, o óxido de grafeno (GO) tornou-se um material de grande interesse físico e tecnológico e não só um material intermediário na síntese de grafeno, mas também como um produto para aplicações diretas. Na tentativa de tornar o GO mais próximo do grafeno, estruturalmente e tecnologicamente falando, o material passa por um processo de redução dos grupos funcionais oxigenados aderidos. Entretanto esse processo de redução não consegue retirar totalmente os grupos funcionais, e a esse material não completamente livre de grupos baseados no oxigênio damos o nome de óxido de grafeno reduzido (rGO). O rGO ao longo dos últimos anos se tornou alvo de pesquisas e muitas aplicações científicas e tec-nológicas como, por exemplo, em dispositivos eletrônicos orgânicos, como diodos emissores de luz (OLEDs), células solares, entre muitos outros. Para tornar este material ainda mais interessante para a área de eletrônica orgânica, propomos a dopagem das nossas moléculas de óxido de grafeno reduzido (rGOm) com átomos de boro, nitrogênio, alumínio silício, fósforo, gálio, germânio e arsênio, um de cada vez e de forma substitutiva. Nosso objetivo e´ fazer com que nosso material se torne um melhor condutor, mantendo ou melhorando sua transparência, pensando no uso deste material como eletrodos em dispositivos orgânicos. Neste trabalho, objetivamos estudar nossas moléculas de óxido de grafeno reduzido (rGOm) nos seus aspectos estruturais e eletrônicos, utilizando métodos semi-empíricos e ab initio a nível DFT, implementados nos programas GAMESS e MOPAC. Usamos como modelos de rGO estruturas contendo 42, 84 e 154 átomos, derivados da molécula de coroneno com adição de três grupos funcionais oxigenados: hidroxil, carboxil e epoxi. Começamos o trabalho fazendo uma busca conformacional da estrutura das nossas rGOm incluindo cada grupo funcional oxigenado ligado aos carbonos dos coronenos. Estudamos as rGOm juntamente com a dopagem, substituindo carbonos na estrutura pelos seguintes átomos: nitrogênio (N), boro (B), fósforo (P), silício (Si), alumínio (Al), arsênio (As), germânio (Ge) e gálio (Ga). Substituímos um átomo da folha de carbono de cada vez. Analisamos o gap de energia entre os estados eletrônicos de fronteira do material, a fim de encontrar tanto o sítio com menor energia total como o sítio com menor valor de gap. Realizamos os cálculos de energia e valor de gap das dopagens mencionadas acima em diferentes níveis de métodos, utilizamos tanto métodos semiempírico (PM3, PM6), quanto DFT (B3LYP, com base 6-31G), fizemos também comparação entre diferentes tipos de aproximação (UHF e RHF) com o objetivo de saber se essas aproximações eram compatíveis entre sícomparando energia total, gap e geometria. Por fim, um dos principais resultados foi a dopagem da rGOm com alumínio. O alumínio quando colocado em alguns sítios específicos promove a aproximação dos orbitais de fronteira, diminuindo o gap, tornando a rGOm do-pado com alumínio um material com propensão a melhor condução elétrica que a rGOm sem dopagem, o que aumenta o interesse na utilização deste material para eletrônica orgânica.
Recently, graphene oxide (GO) has become a material of great physical and technological interest and not only an intermediate material in the synthesis of graphene, but also as a product for direct applications. In an attempt to make GO closer to graphene, structurally and technologically speaking, the material undergoes a process of reduction of adhered oxygenated functional groups. Howe-ver, this reduction process does not completely remove the functional groups, and this material which is not completely free of oxygen-based groups, is called redu-ced graphene oxide (rGO). Over the past few years, RGO has become the target of research and many scientific and technological applications, such as organic electronic devices such as light-emitting diodes (OLEDs), solar cells, and many others. To make this material even more interesting to the area of organic elec-tronics, we propose the doping of our reduced graphene oxide molecules (rGO m) with boron, nitrogen, silicon aluminium, phosphorus, gallium, germanium and arsenic, one at a time and in a substitute way. Our goal is to make our material become a better conductor, maintaining or improving its transparency, thinking of using this material as electrodes in organic devices. In this work, we aim to study our reduced graphene oxide molecules (rGOm) in their structural and electronic aspects, using semi-empirical and ab initio methods at the DFT level, implemented in the GAMESS and MOPAC programs. We used as RGO models structures containing 42, 84 and 154 atoms derived from the coronon molecule with addition of three oxygenated functional groups: hidroxyl, carboxyl and epoxy. We begin the work by making a conformational search of the structure of our rGOm including each oxygenated functional group attached to the carbon atoms of the coronenes. We study the rGOm along with doping, replacing carbons in the structure with the following atoms: nitrogen (N), boron (B), phosphorus (P), silicon (Si), aluminium (Al), arsenic, germanium (Ge) and gallium (Ga). We replace one atom of the carbon sheet each time. We analyzed the energy gap between the border electronic states of the material in order to find both the site with the lowest total energy and the site with the least gap value. We performed the energy calculations and gap value of the above-mentioned dops at different levels of methods, we used both semi-empirical methods (PM3, PM6) and DFT (B3LYP, based on 6-31G), we also compared different types of approximations (UHF and RHF) in order to know if these were compatible with each other comparing total energy, gap and geometry. Finally, one of the main results was the doping of rGOm with aluminium. Aluminium when placed at some specific sites promotes the approach of border orbitals by reducing the gap, making aluminium-doped rGOm a material with a propensity for better electrical conduction than rGOm without doping, which increases the interest in using this material for organic electronics.

碩士
南台科技大學
機械工程系
97
Both 2024-T3 and 7075-T6 are heat treatable aluminum alloys which have been applied widely in aerospace industry, due to their high specific strength and corrosion resistance. However, if the welding parameters for the aluminum alloy are inappropriately specified during the traditional welding process, defects such as high porosity and solidification cracking can occur easily. Friction stir welding (FSW), which is different from traditional arc welding, is used on welding process conducted under the melting point, and is an emerging solid-state joining process that produces low-distortion and high-quality welds. FSW will effectively better general welding quality. In this study, FSW processes are conducted on 2024-T3 and 7075-T6 aluminum alloys, 3mm thick. The major areas discussed were, the effect of the welding parameters, the microstructures and hardness in different tool pin shapes (threaded cylindrical, threaded triangular). The results show that the grain size of both tool pin shapes was significantly reduced in the fixed rotation speed after welding, but the hardness of the weld increased. This is because the input heat decreases with welding speed increasing. This increasing trend of hardness was not apparent for the threaded triangular pin shape. However, the hardness of the weld in the 2024-T3 alloy increased, and in the 7075-T6 decreased while welding speed was fixed and the rotation speed increased. This can be attributed to the different internal precipitation mechanisms of the two materials. When either fixed rotation speed or welding speed was changed the welding quality for threaded triangular was found to be better than that for the threaded cylindrical tool pin. In addition, the threaded triangular tool pin allows greater plastic flow, with the 2024-T3 specimen having a greater amount of plastic flow than the 7075-T6. The results for the different welding materials indicated that as the rotation speed increased, there was a tendency for weld appearances to become more homogenous and the threaded triangular tool pin was better. In term of hardness, the hardness of specimens using both types of tool pins was improved as the rotation speed and the welding speed were increased. For the hardness of the TMAZ and HAZ located at the two sides of the specimens, the retreating side in 2024-T3 was better than its advancing side. Between the tool pins, the threaded triangular was providing higher hardness than the threaded cylindrical pin. In the specimen AS(2024)-RS(7075), the tensile strength and elongation ratio of the weld increased when the rotation speed and the welding speed were increased for the threaded triangular tool pin. However, in the case of the threaded cylindrical tool pin, both tensile strength and elongation ratio decreased. Furthermore, the tensile strength and elongation of AS(7075)-RS(2024) was generally lower than that of AS(2024)-RS(7075). For the tool pin shape, threaded triangular was better.

Surface texturing to achieve reduced sliding friction has been a widely studied topic, as seen in contemporary literature. Laser surface texturing, grinding and ion beam milling are popular techniques accepted by researchers today for creating specific surface textures. Among these, grinding is a popular process adopted today in mass manufacturing around the world. In this study, we look at grinding as a method of surface texturing and studying the effect of various grinding parameters on the friction when sliding a relatively softer material against the generated surface. The system chosen was aluminum pins sliding against a stainless steel surface on which specific textures were generated. The specific system was chosen as an aluminum-steel pair is increasingly used in automobiles as weight reduction is a priority for automobile engine manufacturers today. Automobile engine manufacturers are increasingly shifting to aluminum cylinder blocks to make their power-trains lighter. The tribo-system was lubricated with the mineral base oil used in a SAE 30 grade engine oil blends. The tribo-system was in reciprocating sliding motion, driven by a scotch yoke mechanism similar to that used in a reciprocating internal combustion engine. Though aluminum-silicon alloys and steel are widely used in engines, pure aluminum and stainless steel was chosen in this study for a fundamental understanding of the different parameters involved in an aluminum-steel tribo-system. Aluminum being softer than Al alloys will deform at the asperity level and in oxidation will be much lower in stainless-steel, thus avoiding tribo-oxidation mechanisms operating. Different topographies were created on stainless steel using the conventional grinding methods and differentiated for their effect on sliding friction using a reciprocating tribometer. Different surface topographies were created on a lab scale table grinder using coated abrasive sheets. Sliding friction between an aluminum pin and these stainless steel flats under contact pressures not exceeding 7.5 MPa (similar contact pressures existing in an IC engine – This has to be checked) were tested in a s parsely lubricated sliding environment. Certain surface topographies showed an extraordinary reduction in the average coefficient of sliding friction. The average surface roughness of the topographies that showed lower friction was not different from topography of others that showed higher friction. Separate topographies were created on the stainless steel mirror finished countersurface corresponding to P1200, P320 abrasive disc. Group 1 virgin mineral base oils viz. SN500, SN150 and SN60 with viscosities 100, 30 and 12 cSt at 40 deg C were used. The topographies when tested for cycle average coefficient of friction revealed that P1200 finished surface showed an exceptionally low value under 0.02. In a scotch yoke mechanism, the velocity varies according to a sine curve with maximum velocity occurring at the center and with zero velocities at the ends. This would mean that the lubrication regimes, as given by the Stribeck curve would change from boundary lubrication at the ends to a possible hydrodynamic lubrication when the velocity reaches a maximum. Therefore, it was decided to understand the evolution of the frictional force response of these topographies for each reciprocating cycle. When the individual cycle friction force response was examined in greater detail along with other components in the tribo-system, it was found that the behavior of these plots was significantly different from those predicted by classical Stribeck principles. For the mirror finished stainless-steel flat surface while sliding with the aluminum pin at 1Hz or 40 mm/s average sliding velocity showed a frictional force plot as shown in figure I below. The alternating “M” and “W” patterns corresponded to the frictional force variations when the velocity of sliding varied in a sinusoidal manner corresponding to the velocity profile of the scotch yoke follower mechanism. This variation could be explained well using the classical Stribeck curve where coefficient of friction is expected to reduce as the velocity is increased from zero at the extremes of the track to a maximum at the center of the track, which is defined by the amplitude and frequency of reciprocation. When a P1200-finished surface was tested for 1800 cycles at the same average velocity, the frictional force was as shown below in figure II. The plots showed extremely low frictional force. Frictional force corresponding to the accelerating region was the only response visible and the rest of the cycle approached near zero frictional force. Different average velocities of sliding, viz. 12 mm/s, 40 mm/s, 80 mm/s and 200 mm/s corresponding to 0.3Hz to 1Hz, 2Hz and 5Hz reciprocating frequencies respectively were tested. The tests were carried out for the same number of cycles for a P1200 finished surface. As the sliding velocities were increased from 1 Hz to 5Hz, faster transitions to a steady state was observed. At 1Hz, the system reaches a steady state at about 1000 cycles. At 2Hz, the steady state was reached after around 500 cycles and at 5Hz, the system seemed to reach the steady state from the initial few cycles. It was felt that there were some modifications happening on the aluminum pin surface and/or stainless steel flat countersurface as the test progressed. This change happens at a faster rate and the system reached a steady state faster when the relative velocities of sliding were higher. Thus, for the test conducted at the lowest frequency of 0.3Hz there was no change in the shape of the frictional force plots till the end of the test and friction remained high. The above tests were also done for other topographies viz. mirror and P320 finished surfaces. At velocity corresponding to 5Hz, even the mirror finished surface exhibited extremely low friction and showed nearly flat friction response curves. At low velocities corresponding to 0.3Hz, the adherence to the Stribeck curve phenomenon was seen for all three topographies. It was also observed that a critical film thickness had to be exceeded for this phenomenon of friction reduction to take place. It was found that either an increase in sliding speed or an increase in the oil viscosity enabled the tribo-system to achieve this minimum critical film thickness. Critical three-dimensional areal surface parameters were found out for these topographies using an optical profilometer, and a few parameters governing the shape of these frictional plots were identified. It was found that surface parameter ratio Spk/Sk, where Spk is the reduced peak height and Sk is the core roughness depth, could predict the shape and magnitude of the frictional Fx forces under sliding reciprocating motion for the above tribosystem. Conventionally Spk/Sk ratio is used to distinguish surface topographies which cannot be distinguished by the characteristic average surface roughness and root mean square surface roughness parameters. Spk/Sk highlights the importance of peak structures on a topography. The volume occupied by the peaks in relation to the core roughness and the symmetry in the texture amplitude increased with increase in this surface parameter ratio. Three different types of topographies generated using the same abrasive disc: P320, by using different amounts of grinding fluid (here water) were studied. Conventional surface parameters like average surface roughness and root mean square roughness could not distinguish these three surfaces. However, using the ratio Spk/Sk, it was found that two of these surfaces had Spk/Sk ratio less than 1, and the other surface had this ratio greater than unity. Where the ratio Spk/Sk was less than 1, the frictional force plots did not reduce with the number of cycles and showed adherence to classical Stribeck curves with alternating “M” and “W” shapes. Where Spk/Sk ratio was greater than 1 the friction force reduced with the number of cycles, as seen in figure I and almost became flat and near zero at steady state. It was found that the topography of the stainless-steel countersurface had an influence on the evolution of the aluminum pin topography during sliding. Where the friction force curves resembled figure I, the pin topographies got modified as the Spk/Sk value shifted to a value greater than 1; it was also observed that an evenly spread layer of iron was dispersed on the pin face after the system reached steady state. Where the friction force curves did not reduce with the number of cycles (figure II), there was neither a change in the pin topography nor formation of any tribo-layer as noted above. It was also found that this progressive tribo transfer layer was selectively formed on the pin surface when the friction was extremely low. Some physical explanations have been developed for why the value of the Spk/Sk parameter is important in determining friction in this mating combination. The importance of the pin topography and tribo-layer was evident from different shapes of the frictional force plots with changing pin topographies. When a mild abrasive was used to abrade the pin face after the system reached the steady state, the tribo-layer formed on the pin face was removed and the topography also changed. An immediate shift in the shape of the force plots when the test resumed. Here it was also found that rubbing such a pin on a “used” flat face did not bring the system back to steady state even after continued sliding in successive tests. However, shifting the pin to a “virgin” flat face on the same topography brought the system back to steady state. The sharp tipped peaks on “virgin” stainless-steel flat topography fractured while in sliding contact with the pin and contributed to the quick reformation of the tribo-layer on the countersurface of the pin. It was also found that wear debris did not have any contribution to the shape of the Fx plots. It follows that a combination of the pin topography observed at steady state and the tribo-layer is responsible for reduction in sliding friction to such a low level for certain topographies

Hot extrusion of aluminum is widely practiced in industries for economic production of structural components. The surface finish and tolerance of the extruded components, both from design and aesthetic requirement, are important parameters. Hot extrusion involves forcing of aluminum in the form of a billet at a predetermined temperature through a shaped opening called die. Attempts, over time, are made to evolve the die profile to produce quality components. The main geometric feature of the die enables it in imparting plastic deformation and subsequent surface generation of the extrudate. The surface of extrudate is generated on the portion of the die called bearing channel or die land. Aluminum metal which moves relative to bearing channel experiences a different state-of-stress as it passes through the bearing channel. At the entry side of the bearing channel, the stress is compressive which is large in magnitude and this magnitude of compressive stress gets diminished as metal moves towards exit side and eventually becomes zero at the exit. Temperature gradients and its distribution along the bearing channel, similar to stress gradient, are reported. Literature reports formation of the transfer layer on the bearing channel. The transfer layer is of two distinctive types, the one near entry side which virtually leads to contact between aluminum and die steel and the other nearer to exit side which isolates aluminum from die steel. The understanding of the mechanism of formation of transfer layer is most important since it is instrumental in determining the surface finish of the extruded component. All of the previous studies were conducted either in an actual extrusion press or using an instrumented extrusion press in the laboratory. The variables during these experiments could be the temperature of billet, extrusion ratio and speed of ram. Conducting these experiments using extrusion press is expensive and time consuming. To do experiments where the condition in a bearing channel can be simulated would be useful in conducting a more comprehensive study. To simulate the condition in the bearing channel a high temperature vacuum based pin-on-disc machine is designed and built. The fact that in a bearing channel there is virtually metal to metal contact with minimal or no chance of any intervening oxide layer, necessitated studies to be conducted under vacuum. A pin-on-disc test conducted under vacuum and high temperature would almost simulate condition on a bearing channel. Using this specially designed and built experimental setup the parameters influencing the transfer layer formation, temperature, sliding speed, load on the specimen, vacuum level and surface characteristics of the die are studied. Another feature of the test rig is that the configuration of pin and disc setup is vertical, which is different from regular pin on disc tribo-system, where pin and disc are held in horizontal configuration. The advantage of holding in vertical configuration is to eliminate the possibility of trapping the debris which alters the existing friction force and conditions. The test rig is constructed using a cylindrical shell and a matching dome shell. The test rig, to facilitate the isolation of the instrumentations used to measure the forces and wear from the heat source is partitioned into two portions. The cylindrical bottom compartment called test chamber and dome shaped top compartment called sensor chambers are separated by a plate. On the plate in the sensor chamber, a load-cell to pickup friction force, a linear variable differential transformer (LVDT) to measure linear wear and loading lever mechanisms for imparting normal load and measuring friction force are fitted. The lever mechanism, in particular the one which magnifies the normal load is designed to conserve the space in the vacuum chamber. Housing the instrumentation inside the vacuum chamber thereby reducing the number of ports required to sense mechanical signals, increases the efficiency of the pumping system. The cylindrical shell of the testing chamber is a double walled structure and water cooled in order to prevent the exposer of sensors to higher testing temperature. Rubber ‘O’ rings are used, wherever it is required to seal the vacuum. The necessary temperature required at the contact interface in the testing chamber is obtained by an electric resistance furnace, which is configured in such a way in the chamber that the heat generated is completely directed to the area where pin and disc are positioned. The interface temperature is monitored using a chromal-alumal thermocouple which is fixed very close to sliding interface on the pin holder. The power input to the furnace is controlled using PID (proportional integral derivative). The required sliding speed is achieved with the help of direct current (DC) servomotor. The shaft on which the disc or ring is fixed is connected to a timer-pulley. The timer-pulley in turn is connected to servomotor through a timer-belt. The diameter ratio of the driving pulley and driven -timer-pulley is selected in such a way that the rpm of driven-pulley is reduced by four times and the torque increased by four times resulting in a more stable mechanical input to the sliding pair. The necessary high vacuum level in the test chamber is created by using rotary pump and diffusion pump combination. Following tests are carried out. 1. Compression test: The strain rate response of aluminum (6060) under compressive state of loading is studied at strain rates 10-3s-1, 10-2s-1, 10-1s-1, 1s-1, 10s-1 and 102sand temperature ranging from 573 to 823K. The compression specimen is machined out of homogenized aluminum alloy (6060) cast ingots. True stress and true strain are estimated from load-displacement data of compression test. The true stress and true strain data are made use of in predicting the friction coefficient and sliding mode during sliding of aluminum relative to die steel at various temperature and other independent variables in vacuum. 2. The tensile test: A series of tensile tests at different temperatures and 10-1s-1 strain rate are conducted. The temperatures employed are from 423K to 723K. True stress, true strain, ultimate tensile strength and total percentage of elongation are estimated using load displacement data. The estimated ultimate tensile strength and total percentage of elongation are used for qualitatively explaining the morphology of transfer layer formed in the sliding experiments under different independent variables like temperature, speed, normal load, and surface texture of steel surface. 3. Adhesion test: The interaction at different temperature between the die steel (H11) and aluminum (6060) pair under static load is studied by conducting test in vacuum. The pin is made of homogenized aluminum and disc is made of die steel whose surface is generated by polishing on diamond paste until the average surface roughness (Sa) is of the order of 0.1 microns. The test temperatures are varied from 423 to 723K. The result is used in qualitatively explaining the morphology of transfer layer formed during sliding of aluminum and die steel pair in vacuum at various temperature, speeds and, normal load. 4. Sliding experiment: Steel pin and aluminum disc Pin on disc experiments are conducted at different temperatures in vacuum of the order of 4X10-4Pa. The experiments are conducted employing factorial design. The temperature, speed and load are the experimental parameters. The pin and disc are respectively made out of die steel and aluminum. Experiments are carried out with normal loads 20N, 40N, 63N, 80N, and 100N and speeds 0.1ms-1, 0.3ms-1, 0.5ms-1, 1.0ms-1, and 1.5ms-1 and with temperature over a range from 423 to 773K. The sliding distance covered is 500 meters. The friction force during sliding is monitored and used for estimating friction coefficient. Scanning electron microscopic study is carried out on surface, subsurface, wear track. The results, specifically, the friction coefficient and morphology of transfer layer are used to evaluate the influence of independent parameters on transfer mechanisms. The data generated from subsurface study and compression tests are used for estimating friction coefficient using Rigney’s plastic deformation model at 0.1ms-1. 5. Sliding experiment: aluminum pin and Steel disc The experiments reported in the previous paragraph where aluminum disc is slid against die steel pin had developed only the stresses of the order 16MPa. The estimated magnitude of stress level on bearing surface of extrusion die by various methods including numerical analysis is found to be more than 16MPa. In order to achieve a higher magnitude of stress and preserve the transfer layer mechanism, sliding an aluminum pin over the part of the textured surface of die steel ring is carried out. The changed boundary condition resulted in a nominal stress of 28 MPa which is comparatively more at 723K. The experiments are conducted employing factorial design. The other advantage of doing these experiments is that the effect of texture on the die surface can be studied by sliding aluminum pin over various surfaces. Thus temperature and surface texture are the experimental parameters for the present test. Different textured die steel surface is generated by machining process like, milling, electro discharge machining (EDM), wire electro discharge machining, silicon carbide slurry polishing, silicon carbide wheel grinding, CNC-milling and diamond paste polishing. Thus surfaces are basically of two types 1) with a lay on the surface and 2) a random surface. The tests are conducted at ambient temperature, 423, 573, 673, and 723K with a normal load of 56N and speed of 0.129ms-1. The morphology of transfer layer on the die steel ring is studied in scanning electron microscope. The friction coefficient is estimated from monitored friction force. The average surface roughness (Sa), results of compression test, and transfer layer are made use of to identify the sliding mode. The sliding of aluminum pin on diamond polished surface showed interesting results. Hence, another series of experiments using only diamond polished surface are conducted. The surface roughness of the steel surface achieved is 0.05 micro-meters. The load is 47N and speed is 0.043ms-1. The morphology of transfer layer and pin surface is studied using a Scanning Electron Microscope. Results of compression and tensile test: The flow stress is found to decrease with increase in compression test temperature. The SEM micrograph indicates large amount of fragmentation of harder phase with increase in strain rate at all temperature except for 423K. The fractured surface under tensile loading shows both intergranular and transgranular failure. Results of adhesion test: The area covered by the material transfer is found to increase with increase in temperature. The test can be used, to study the adhesive tendency between two pair of contacting surfaces. The area covered by the material transfer is found to be maximum at 723K. Results of sliding of die-steel pin on aluminum disc in vacuum: 1. The ANOVA (analysis of variance) results indicate the existence of transition speed of about 0.5ms-1, more than which the friction coefficient was found constant. The extrusion speeds employed in industries are in the range of 0.1ms-1 to 1.7ms-1 and the transition speed found in the present study is within this range. 2. The magnitude of friction, with a few exceptions, is found to be independent of temperature and sliding speed when the sliding speed is 0.5ms-1and above. The invariance of friction coefficient with temperature and sliding speed beyond 0.5ms-1 is beneficial in that it will not lead to any instability like stick-slip or squeal. 3. Though both ambient temperature and speed influence the morphology of transfer layer and friction coefficient, speed is found to be dominant according to statistical analysis. 4. The observed dependency of friction coefficient and morphology of transfer layer on test temperature and normal load is attributed to decrease in flow stress and increase in friction factor ‘m’, a ratio of interfacial shear stress to shear yield stress of the softer material. Though ANOVA shows the significance of speed and not that of temperature, the observed dependence of friction coefficient on temperature is attributed to the enhanced effect of adhesion at elevated temperature observed in the adhesion test. 5. The state of stress at the contacting surface is found to control the morphology of transfer layer. When the normal load exceeded 40N, it gave rise to higher magnitude of stress state at the contacting surface, resulting in formation of continuous transfer layer and hence the higher magnitude of friction coefficient. 6. Plastic deformation model based on Rigney’s approach for estimating friction coefficient can be used. The estimated friction coefficient is on the higher side. Hence, any design of equipments based on the Rigney’s plastic deformation model is a conservative design. 7. There appears to be a close relation between the morphology of wear track and quantity of wear-loss. The formation of debris and rough track, primarily for low temperature sliding indicate larger magnitude of wear-loss. The parameters, which bring about increased ductility of aluminum as observed in the case of higher temperature of sliding, results in reduced wear-loss due to large scale smearing and back transfer of material. The results of sliding of aluminum pin on die-steel ring in vacuum: 1. The mode of sliding changes from adhesive to abrasive mode depending on depth of penetration, tan(θ) where θ is the base angle of the conical asperity and average roughness parameter Sa ,all of them in turn depend on morphology of die steel surface and test temperature. 2. The friction coefficient and morphology of transfer layer are found to depend on the mode of sliding. The sub-surface plastic deformation, which characterizes the friction coefficient and morphology of transfer layer, is dependent on temperature of sliding. 3. The sliding experiment is capable of simulating the stress state on the bearing channel of the die; elucidating evolution of transfer layer, with change in operating parameters. 4. The ANOVA has clearly indicated the significance in friction coefficient at different temperatures and surface textures. In addition, the complex comparison below and above homogenization temperature (573K) has indicated significance in friction coefficient and thereby recognizing the importance of extrusion of aluminum at a temperature where it is in a single phase. Also, ANOVA indicates the dependency of both friction coefficient and transfer layer on the texture, i.e. either a lay or random. The results of sliding aluminum pin on diamond polished die steel ring: 1. Shearing of the cold welded junction is a probable mechanism involved in the formation of transfer layer up to 423K. 2. The transgranular and intergranular mode of fracture are identified to be the two possible modes of fracture of the asperity at temperatures greater than 573K. The large ductility of the aluminum alloy facilitated smearing resulting in a continuous transfer layer at temperatures greater than 573K. 3. The formation of a continuous transfer layer at temperatures greater than 573K is responsible for the observed high friction coefficient at these temperatures. Scanning electron microscopy observations of the fracture surfaces of the tensile test specimen revealed fracture to be a combination of both transgranular and intergranular modes.

Hot extrusion of aluminum is widely practiced in industries for economic production of structural components. The surface finish and tolerance of the extruded components, both from design and aesthetic requirement, are important parameters. Hot extrusion involves forcing of aluminum in the form of a billet at a predetermined temperature through a shaped opening called die. Attempts, over time, are made to evolve the die profile to produce quality components. The main geometric feature of the die enables it in imparting plastic deformation and subsequent surface generation of the extrudate. The surface of extrudate is generated on the portion of the die called bearing channel or die land. Aluminum metal which moves relative to bearing channel experiences a different state-of-stress as it passes through the bearing channel. At the entry side of the bearing channel, the stress is compressive which is large in magnitude and this magnitude of compressive stress gets diminished as metal moves towards exit side and eventually becomes zero at the exit. Temperature gradients and its distribution along the bearing channel, similar to stress gradient, are reported. Literature reports formation of the transfer layer on the bearing channel. The transfer layer is of two distinctive types, the one near entry side which virtually leads to contact between aluminum and die steel and the other nearer to exit side which isolates aluminum from die steel. The understanding of the mechanism of formation of transfer layer is most important since it is instrumental in determining the surface finish of the extruded component. All of the previous studies were conducted either in an actual extrusion press or using an instrumented extrusion press in the laboratory. The variables during these experiments could be the temperature of billet, extrusion ratio and speed of ram. Conducting these experiments using extrusion press is expensive and time consuming. To do experiments where the condition in a bearing channel can be simulated would be useful in conducting a more comprehensive study. To simulate the condition in the bearing channel a high temperature vacuum based pin-on-disc machine is designed and built. The fact that in a bearing channel there is virtually metal to metal contact with minimal or no chance of any intervening oxide layer, necessitated studies to be conducted under vacuum. A pin-on-disc test conducted under vacuum and high temperature would almost simulate condition on a bearing channel. Using this specially designed and built experimental setup the parameters influencing the transfer layer formation, temperature, sliding speed, load on the specimen, vacuum level and surface characteristics of the die are studied. Another feature of the test rig is that the configuration of pin and disc setup is vertical, which is different from regular pin on disc tribo-system, where pin and disc are held in horizontal configuration. The advantage of holding in vertical configuration is to eliminate the possibility of trapping the debris which alters the existing friction force and conditions. The test rig is constructed using a cylindrical shell and a matching dome shell. The test rig, to facilitate the isolation of the instrumentations used to measure the forces and wear from the heat source is partitioned into two portions. The cylindrical bottom compartment called test chamber and dome shaped top compartment called sensor chambers are separated by a plate. On the plate in the sensor chamber, a load-cell to pickup friction force, a linear variable differential transformer (LVDT) to measure linear wear and loading lever mechanisms for imparting normal load and measuring friction force are fitted. The lever mechanism, in particular the one which magnifies the normal load is designed to conserve the space in the vacuum chamber. Housing the instrumentation inside the vacuum chamber thereby reducing the number of ports required to sense mechanical signals, increases the efficiency of the pumping system. The cylindrical shell of the testing chamber is a double walled structure and water cooled in order to prevent the exposer of sensors to higher testing temperature. Rubber ‘O’ rings are used, wherever it is required to seal the vacuum. The necessary temperature required at the contact interface in the testing chamber is obtained by an electric resistance furnace, which is configured in such a way in the chamber that the heat generated is completely directed to the area where pin and disc are positioned. The interface temperature is monitored using a chromal-alumal thermocouple which is fixed very close to sliding interface on the pin holder. The power input to the furnace is controlled using PID (proportional integral derivative). The required sliding speed is achieved with the help of direct current (DC) servomotor. The shaft on which the disc or ring is fixed is connected to a timer-pulley. The timer-pulley in turn is connected to servomotor through a timer-belt. The diameter ratio of the driving pulley and driven -timer-pulley is selected in such a way that the rpm of driven-pulley is reduced by four times and the torque increased by four times resulting in a more stable mechanical input to the sliding pair. The necessary high vacuum level in the test chamber is created by using rotary pump and diffusion pump combination. Following tests are carried out. 1. Compression test: The strain rate response of aluminum (6060) under compressive state of loading is studied at strain rates 10-3s-1, 10-2s-1, 10-1s-1, 1s-1, 10s-1 and 102sand temperature ranging from 573 to 823K. The compression specimen is machined out of homogenized aluminum alloy (6060) cast ingots. True stress and true strain are estimated from load-displacement data of compression test. The true stress and true strain data are made use of in predicting the friction coefficient and sliding mode during sliding of aluminum relative to die steel at various temperature and other independent variables in vacuum. 2. The tensile test: A series of tensile tests at different temperatures and 10-1s-1 strain rate are conducted. The temperatures employed are from 423K to 723K. True stress, true strain, ultimate tensile strength and total percentage of elongation are estimated using load displacement data. The estimated ultimate tensile strength and total percentage of elongation are used for qualitatively explaining the morphology of transfer layer formed in the sliding experiments under different independent variables like temperature, speed, normal load, and surface texture of steel surface. 3. Adhesion test: The interaction at different temperature between the die steel (H11) and aluminum (6060) pair under static load is studied by conducting test in vacuum. The pin is made of homogenized aluminum and disc is made of die steel whose surface is generated by polishing on diamond paste until the average surface roughness (Sa) is of the order of 0.1 microns. The test temperatures are varied from 423 to 723K. The result is used in qualitatively explaining the morphology of transfer layer formed during sliding of aluminum and die steel pair in vacuum at various temperature, speeds and, normal load. 4. Sliding experiment: Steel pin and aluminum disc Pin on disc experiments are conducted at different temperatures in vacuum of the order of 4X10-4Pa. The experiments are conducted employing factorial design. The temperature, speed and load are the experimental parameters. The pin and disc are respectively made out of die steel and aluminum. Experiments are carried out with normal loads 20N, 40N, 63N, 80N, and 100N and speeds 0.1ms-1, 0.3ms-1, 0.5ms-1, 1.0ms-1, and 1.5ms-1 and with temperature over a range from 423 to 773K. The sliding distance covered is 500 meters. The friction force during sliding is monitored and used for estimating friction coefficient. Scanning electron microscopic study is carried out on surface, subsurface, wear track. The results, specifically, the friction coefficient and morphology of transfer layer are used to evaluate the influence of independent parameters on transfer mechanisms. The data generated from subsurface study and compression tests are used for estimating friction coefficient using Rigney’s plastic deformation model at 0.1ms-1. 5. Sliding experiment: aluminum pin and Steel disc The experiments reported in the previous paragraph where aluminum disc is slid against die steel pin had developed only the stresses of the order 16MPa. The estimated magnitude of stress level on bearing surface of extrusion die by various methods including numerical analysis is found to be more than 16MPa. In order to achieve a higher magnitude of stress and preserve the transfer layer mechanism, sliding an aluminum pin over the part of the textured surface of die steel ring is carried out. The changed boundary condition resulted in a nominal stress of 28 MPa which is comparatively more at 723K. The experiments are conducted employing factorial design. The other advantage of doing these experiments is that the effect of texture on the die surface can be studied by sliding aluminum pin over various surfaces. Thus temperature and surface texture are the experimental parameters for the present test. Different textured die steel surface is generated by machining process like, milling, electro discharge machining (EDM), wire electro discharge machining, silicon carbide slurry polishing, silicon carbide wheel grinding, CNC-milling and diamond paste polishing. Thus surfaces are basically of two types 1) with a lay on the surface and 2) a random surface. The tests are conducted at ambient temperature, 423, 573, 673, and 723K with a normal load of 56N and speed of 0.129ms-1. The morphology of transfer layer on the die steel ring is studied in scanning electron microscope. The friction coefficient is estimated from monitored friction force. The average surface roughness (Sa), results of compression test, and transfer layer are made use of to identify the sliding mode. The sliding of aluminum pin on diamond polished surface showed interesting results. Hence, another series of experiments using only diamond polished surface are conducted. The surface roughness of the steel surface achieved is 0.05 micro-meters. The load is 47N and speed is 0.043ms-1. The morphology of transfer layer and pin surface is studied using a Scanning Electron Microscope. Results of compression and tensile test: The flow stress is found to decrease with increase in compression test temperature. The SEM micrograph indicates large amount of fragmentation of harder phase with increase in strain rate at all temperature except for 423K. The fractured surface under tensile loading shows both intergranular and transgranular failure. Results of adhesion test: The area covered by the material transfer is found to increase with increase in temperature. The test can be used, to study the adhesive tendency between two pair of contacting surfaces. The area covered by the material transfer is found to be maximum at 723K. Results of sliding of die-steel pin on aluminum disc in vacuum: 1. The ANOVA (analysis of variance) results indicate the existence of transition speed of about 0.5ms-1, more than which the friction coefficient was found constant. The extrusion speeds employed in industries are in the range of 0.1ms-1 to 1.7ms-1 and the transition speed found in the present study is within this range. 2. The magnitude of friction, with a few exceptions, is found to be independent of temperature and sliding speed when the sliding speed is 0.5ms-1and above. The invariance of friction coefficient with temperature and sliding speed beyond 0.5ms-1 is beneficial in that it will not lead to any instability like stick-slip or squeal. 3. Though both ambient temperature and speed influence the morphology of transfer layer and friction coefficient, speed is found to be dominant according to statistical analysis. 4. The observed dependency of friction coefficient and morphology of transfer layer on test temperature and normal load is attributed to decrease in flow stress and increase in friction factor ‘m’, a ratio of interfacial shear stress to shear yield stress of the softer material. Though ANOVA shows the significance of speed and not that of temperature, the observed dependence of friction coefficient on temperature is attributed to the enhanced effect of adhesion at elevated temperature observed in the adhesion test. 5. The state of stress at the contacting surface is found to control the morphology of transfer layer. When the normal load exceeded 40N, it gave rise to higher magnitude of stress state at the contacting surface, resulting in formation of continuous transfer layer and hence the higher magnitude of friction coefficient. 6. Plastic deformation model based on Rigney’s approach for estimating friction coefficient can be used. The estimated friction coefficient is on the higher side. Hence, any design of equipments based on the Rigney’s plastic deformation model is a conservative design. 7. There appears to be a close relation between the morphology of wear track and quantity of wear-loss. The formation of debris and rough track, primarily for low temperature sliding indicate larger magnitude of wear-loss. The parameters, which bring about increased ductility of aluminum as observed in the case of higher temperature of sliding, results in reduced wear-loss due to large scale smearing and back transfer of material. The results of sliding of aluminum pin on die-steel ring in vacuum: 1. The mode of sliding changes from adhesive to abrasive mode depending on depth of penetration, tan(θ) where θ is the base angle of the conical asperity and average roughness parameter Sa ,all of them in turn depend on morphology of die steel surface and test temperature. 2. The friction coefficient and morphology of transfer layer are found to depend on the mode of sliding. The sub-surface plastic deformation, which characterizes the friction coefficient and morphology of transfer layer, is dependent on temperature of sliding. 3. The sliding experiment is capable of simulating the stress state on the bearing channel of the die; elucidating evolution of transfer layer, with change in operating parameters. 4. The ANOVA has clearly indicated the significance in friction coefficient at different temperatures and surface textures. In addition, the complex comparison below and above homogenization temperature (573K) has indicated significance in friction coefficient and thereby recognizing the importance of extrusion of aluminum at a temperature where it is in a single phase. Also, ANOVA indicates the dependency of both friction coefficient and transfer layer on the texture, i.e. either a lay or random. The results of sliding aluminum pin on diamond polished die steel ring: 1. Shearing of the cold welded junction is a probable mechanism involved in the formation of transfer layer up to 423K. 2. The transgranular and intergranular mode of fracture are identified to be the two possible modes of fracture of the asperity at temperatures greater than 573K. The large ductility of the aluminum alloy facilitated smearing resulting in a continuous transfer layer at temperatures greater than 573K. 3. The formation of a continuous transfer layer at temperatures greater than 573K is responsible for the observed high friction coefficient at these temperatures. Scanning electron microscopy observations of the fracture surfaces of the tensile test specimen revealed fracture to be a combination of both transgranular and intergranular modes.

Le mécanisme menant à des déformations structurales suivant le bombardement d'échantillons de a-Si d'un faisceau d'ions lourds et rapides est sujet de controverses. Nous nous sommes penchés sur l'hypothèse de la formation d'une zone liquide causée par la déposition d'énergie des ions incidents dans le contexte de la théorie du pic thermique. Des échantillons de silicium amorphe furent préparés dans le but d'observer les indices d'une transition de phase l-Si/a-Si suivant la déposition locale d'énergie sur le parcours d'un ion lourd énergétique dans le a-Si. Les échantillons furent implantés d'impuretés de Cu ou d'Ag avant d'être exposés à un faisceau d'ions Ag12+ de 70 MeV. L'utilisation de l'analyse GISAXS est projetée afin d'observer une concentration locale d'impuretés suivant leur ségrégation sur la trace de l'ion. Des masques d'implantation nanométriques d'oxide d'aluminium ont été fabriqués afin d'augmenter la sensibilité de l'analyse GISAXS et une méthode d'alignement de ces masques selon la direction du faisceau fut développée. Le bombardement d'échantillons au travers de ces masques a donné lieu à un réseau de sites d'impacts isolés presque équidistants.
The machanisms underlying structural deformations following swift heavy ion beam a-Si irradiation are subject of debate. We investigated the hypothesis of the presence of a liquid phase in the wake of the energetic ions in the thermal spike framework. a-Si samples were prepared in order to track a transient liquid phase by implanting Cu or Ag on the a-Si surface and exposing the sample to a 70 MeV Ag12+ beam. Cu and Ag are both very sensitive to segregation in Si and are therefore thought to be capable of keeping track of a molten transient state by concentrating on the ion track. Samples are to be investigated with GISAXS. Nanoscale implantation masks were developed from nanoporous alumina membranes in order to impose a pattern on the ion impact sites and thus improve GISAXS sensitivitity. An alignment method is also developed for the positioning of pores parallel to the ion beam direction. A nearly equidistant impact sites pattern was achieved by irradiating fused silica through these implantation masks.

6 ABSTRACT Background The existence of risks of new work-related disorders and occupational diseases in the society is constantly increasing in relation to the fast and continuous development of working conditions, techniques used, materials and overall acceleration of the working pace. Aim of the study The aim of the study is to analyse new risks in the working environment and to evaluate early diagnostic possibilities of new occupational diseases including their prevention. The study also compares the current situation in this field in the Czech Republic and other European countries. Materials and methods The doctoral dissertation is a multiple manuscript thesis focusing on one common topic - new occupational diseases. The first publication studied the acknowledgement of low-back pain disease caused by overload as an occupational disease. Specialists from European countries were inquired via questionnaire focusing on diagnostic and evaluation criteria of this disease in their countries. Representatives from countries acknowledging low-back pain diseases caused by overload provided further evaluation criteria and number of cases. Correspondingly, the second publication studied the evaluation of burnout syndrome as an occupational disease. Representatives from countries acknowledging the burnout syndrome as...