Le 32CrMoV13 nitruré est un matériau à gradient de propriétés utilisé pour la réalisation de bagues de roulements aéronautiques. Il présente l’avantage d’être dur en surface et ductile à cœur, facilitant ainsi la lutte contre les effets de la pollution des contacts par les lubrifiants. De plus, afin d’améliorer les performances des roulements, la tendance est à l’utilisation de céramique (nitrure de silicium Si3N4) pour les éléments roulants à la place de l’acier (M50). Ainsi, le travail de thèse proposé ici est l’étude du comportement en fatigue de contact en présence d’indentations pour deux couples de matériaux (32CrMoV13 nitruré / M50 et 32CrMoV13 nitruré / Si3N4). Ce comportement est principalement orienté en terme de durée de vie du contact indenté par l’intermédiaire d’un critère d’amorçage de fissures. Une étude des propriétés mécaniques du 32CrMoV13 nitruré, nécessaires à l’application du critère, a été réalisée. La loi d’écrouissage et l’ouverture micro-plastique cyclique de la couche nitrurée du 32CrMoV13 nitruré ont été identifiées. Puis, par l’intermédiaire de défauts géométrique de type trous cylindriques, les propriétés d’amorçage de fissures ont été étudiées lors d’essais de compression uniaxiale. Le comportement en fatigue de contact en présence d’indentations a été étudié sur machine bi-disques. Ces essais ont permis de caractériser la différence de comportement du 32CrMoV13 nitruré, et indenté, dans un contact acier / acier et acier / céramique. L’effet du glissement a notamment été mis en évidence. Ces études expérimentales ont été couplées avec des simulations numériques afin d’étalonner le modèle physique d’amorçage de fissures et d’en valider sa bonne représentativité. En conclusion un modèle de prédiction de durée de vie en fatigue de roulement a été proposé. Il est particulièrement adapté aux cas où des contraintes résiduelles sont présentes, par exemple suite à l’indentation des surfaces. Le modèle s’appuie sur la caractérisation mécanique des couches traitées thermo-chimiquement de l’acier 32CrMoV13 nitruré. / The nitrided 32CrMoV13 steel is a gradient properties material used for the production of aeronautical bearing rings. The principal advantages are its surface hardness and core ductility, useful against debris denting. Moreover, to improve rolling bearing performances, ceramic balls (silicon nitride Si3N4) instead of steel (M50). The present study aims to investigate the contact fatigue performance in presence of indentation for two pairs of materials (nitrided 32CrMoV13 steel / M50 and nitrided 32CrMoV13 steel / Si3N4). This performance is mainly oriented in terms of lifetime of the indented contact by a crack initiation criterion. A study of the mechanicals properties of the nitrided 32CrMoV13 steel, required for the application of the criterion, is then performed. It allows to characterize the hardening law and the cyclic micro-plastic behavior of the nitrided layer of the nitrided 32CrMoV13 steel. Crack initiation properties of the nitrided surface layer have been evaluated by compression tests on thin hollow cylindrical specimens with small cylindrical holes. The contact fatigue behavior in presence of indentations was studied on a high-speed twin-disks machine. These tests allowed to characterize the difference in behavior of nitrided 32CrMoV13 steel (indented) in a steel-to-steel contact or steel-to-ceramic contact. The major effect of sliding has been highlighted. All these experimental studies were coupled with numerical simulations to calibrate the physical model of crack initiation and to show its capabilities. In conclusion a new model of rolling contact fatigue life has been proposed. It is specifically adapted to operation in presence of residual stresses such as resulting from debris denting. The model uses mechanical properties that have been identified for thermo-chemically treated layers of nitrided 32CrMoV13 steel.

Šiame darbe atlikti biologinių tepamųjų medžiagų tribologinių savybių tyrimai bei aptariami gauti rezultatai. Tirtas grynas ir sekančiais priedais modifikuotas rapsų aliejus: stearino rūgštimi, oleino rūgštimi, monogliceridais, monodigliceridais bei jų kompozicijomis. Tyrimų rezultatai rodo, kad rapsų aliejus, modifikuotas įvardintomis medžiagomis bei jų mišiniais, efektyviau slopina dilimą, o trintį mažina efektyviau net už komercines biologines alyvas. Nnustatyta, kad rapsų aliejus modifikuotas oleino rūgštimi geriau slopina dilimą lyginant su grynu rapsų aliejumi. Rapsų aliejaus mišinys su 2% oleino rūgšties ir 0,5% monodigliceridų priedais ne tik užtikrina mažus trinties nuostolius tribosistemoje, bet šie nuostoliai viso standartinio keturių bandymo metu turi tendenciją mažėti. / At this work there are accomplished researches of biological properties of lubricating materials bio-tribological features and disputed obtained results. This work discusses bio-tribological properties of lubricating materials results. Tests were used rapeseed oil additives modified next: stearic acid, oleic acid, monoglycerides, monodiglycerides and their compositions. Investigation shows, that the modification of rapeseed oil substances and mixtures there of effectively inhibits wear and effectively reduces friction, even for commercial bio oil. The investigation revealed that the modified rapeseed oil oleic acid improves friction surfaces to wear protection. It was found that a mixture of rapeseed oil with 2% oleic acid and 0.5% monodiglycerides accessories not only ensure the minimum of friction losses in the moment, but these losses during the test have a tendency to decrease.

Selective laser melting (SLM) is a powder-based additive manufacturing technique consisting of the exact reproduction of a three dimensional computer model (generally a computer-aided design CAD file or a computer tomography CT scan) through an additive layer-by-layer strategy. Because of the high degree of freedom offered by the additive manufacturing, parts having almost any possible geometry can be produced by SLM. More specifically, with this process it is possible to build parts with extremely complex shapes and geometries that would otherwise be difficult or impossible to produce using conventional subtractive manufacturing processes. Another major advantage of SLM compared to conventional techniques is the fast cooling rate during the process. This permits the production of bulk materials with very fine microstructures and improved mechanical properties or even bulk metallic glasses. In addition, this technology gives the opportunity to produce ready-to-use parts with minimized need for post-processing (only surface polishing might be required). Recently, significant research activity has been focused on SLM processing of different metallic materials, including steels, Ti-, Ni- and Al-based alloys. However, most of the research is devoted to the parameters optimization or to feasibility studies on the production of complex structures with no detailed investigations of the structure-property correlation. Accordingly, this thesis focuses on the production and structure-property correlation of Al-12Si samples produced by SLM from gas atomized powders. The microstructure of the as-prepared SLM samples consists of supersaturated primary Al with an extremely fine cellular structure along with the residual free Si situated at the cellular boundaries. This microstructure leads to a remarkable mechanical behavior: the yield and tensile strengths of the SLM samples are respectively four and two times higher than their cast counterparts. However, the ductility is significantly reduced compared with the cast samples. The effect of annealing at different temperatures on the microstructure and resulting mechanical properties of the SLM parts has been systematically studied by analyzing the size, morphology and distribution of the phases. In addition, the mechanical properties of the SLM samples have been modeled using micro- structural features, such as the crystallite and matrix ligament sizes. The results demonstrate that the mechanical behavior of the Al-12Si SLM samples can be tuned within a wide range of strength and ductility through the use of the proper annealing treatment. The Al-Si alloys are generally used as pistons or cylinder liners in automotive applications. This requires good wear resistance and sufficient strength at the operating temperature, which ranges between 373 – 473 K. Accordingly, the tensile properties of the SLM samples were also tested at these temperatures. Changing the hatch style during SLM processing vary the texture in the material. Hence, samples with different hatch styles were produced and the effect of texture on their mechanical behavior was evaluated. The results show that the hatch style strongly influences both the mechanical properties and the texture of the samples; however no direct correlation was observed between texture and mechanical properties. The wear properties of the Al-12Si material was evaluated using pin-on-disc and fretting wear experiments. These experiments show that the as-prepared SLM samples exhibit better wear resistance than their cast counterparts and the SLM heat-treated samples. Finally, the corrosion investigations reveal that the SLM samples have similar corrosion behavior as the cast specimens under acidic conditions. A major drawback for the wide application of SLM as an industrial processing route is the limited size of the products. This is a direct consequence of the limited dimensions of the available building chambers, which allow for the production of samples with volumes of about 0.02 m3. A possible way to overcome this problem would be the use of the welding processes to join the small SLM objects to form parts with no dimensional limitations. In order to verify this possibility, friction welding was employed to join Al-12Si SLM parts. The results indicate that friction welding not only successfully permits the join materials manufactured by SLM, but also helps to significantly improve their ductility. This work clearly demonstrates that SLM can be successfully used for the production of Al-12Si parts with an overall superior performance of the mechanical and physical properties with respect to the conventional cast samples. Moreover, the mechanical properties of the SLM samples can be widely tuned in-situ by employing suitable hatch styles or ex-situ by the proper heat treatment. This might help the development of SLM for the production of innovative high-performance Al-based materials and structures with controlled properties for automotive and aerospace applications.

No description available.

Made available in DSpace on 2017-07-21T19:26:00Z (GMT). No. of bitstreams: 1 Andre Assmann.pdf: 3125745 bytes, checksum: 38854736eae2fcc4e8c2c21a2668f387 (MD5) Previous issue date: 2011-04-27 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / In the present work showing the results on mechanical and tribological properties of duplex stainless steel LDX2101 nitriding by Ion Implantation (II), Plasma Immersion Ion Implantation (PI3) and Glow Discharge (GD). Nitrogen ion implantation was performed at room temperature and 350 C. The nitrogen fluencies were combined to obtain an atomic nitrogen concentration of 27 %. The PI3 was carried out with temperatures of 300 and 350 C working in N2 atmosphere during 3 hours. For GD, the working conditions were gas mixture N2/H2 (in the ratio 80%/20%, 60%/40% and 20%/80%) and N2/CH4 (in the ratio 98%/02%) during 3 hours at temperatures of 300, 350 and 380 C. Structural characterizations of the modified layers were performed by X-Ray Diffraction (XRD) with Bragg-Brentano geometry. Hardness was obtained by instrumented indentation using Oliver and Pharr method’s with Berkovich indenter. Tribological tests were evaluated by reciprocating sliding with a WC(Co) sphere (counter body). XRD patterns for II samples showing only the formation of γN, however, samples treated by GD and PI3 showed the formation of γ’Fe4N and Fe2+XN, over there γN, as a function of the working temperature and nitriding atmosphere. After the nitriding hardness values between 8 and 20 GPa in comparison to 3 GPa of the bulk was obtained. The hardness profile of samples treated by GD at 350 and 380 C exhibit plateaulike for values of hardness between 13 and 20 GPa, indicate the formation of a thicker nitrited layer. The friction coefficient for II samples showed a strong adhesive wear. PI3 samples exhibit long running-in regimes compared to II and untreated samples. GD samples showing a predominant abrasive wear because ploughing of surface for asperities and wear particles formed between the surface and counter body. The significant decrease in the wear was observed in all GD samples, with a reduction of one order of magnitude compared to untreated sample. / No presente trabalho, são apresentados os resultados sobre as propriedades mecânicas e tribológicas do aço inoxidável duplex LDX 2101 nitretado por Implantação Iônica (II), Implantação Iônica por Imersão em Plasma (3IP) e Descarga Luminosa (DL). A Implantação Iônica de nitrogênio foi realizada em temperatura ambiente e em 350 C. As fluências utilizadas foram combinadas para obter uma concentração de átomos de nitrogênio de 27 %. A nitretação 3IP, foi realizada nas temperaturas de 300 e 350 C em atmosfera de N2 durante 3 horas. Para o tratamento por DL as condições de tratamento foram em diferentes atmosferas de N2/H2 (nas proporções de 80%/20%, 60%/40% e 20%/80%) e N2/CH4 (na proporção de 98%/02%) durante 3 horas nas temperaturas de 300, 350 e 380 C. A caracterização estrutural das camadas modificadas foi obtida através de Difração de Raios-X (DRX) com geometria Bragg-Brentano. Os perfis de dureza foram obtidos por indentação instrumentada usando o método de Oliver e Pharr com indentador do tipo Berkovich. Testes tribológicos foram realizados com tribômetro do tipo pino sobre disco em movimento recíproco com uma esfera de WC(Co) de contra corpo. Os padrões de DRX para amostras tratadas por II apresentaram apenas a formação de γN, contudo, as amostras tratadas por DL e 3IP apresentaram a formação de γ’-Fe4N e Fe2+XN, além de γN, como função da temperatura de tratamento e da atmosfera de nitretação. Após as nitretações durezas entre 8 e 20 GPa em comparação a 3 GPa para o substrato foram obtidas. Perfis de dureza para amostras tratadas por DL em 350 e 380 C exibiram valores entre 13 e 20 GPa em forma de platô, indicando a formação de uma espessa camada nitretada. O coeficiente de atrito para as amostras tratadas por II apresentaram um forte desgaste adesivo. Amostras tratadas por 3IP exibiram longos regimes de acomodação comparados as amostras tratadas por II e a amostra referência. Amostras tratadas por DL apresentaram um predominante desgaste abrasivo devido à deformação plástica da superfície causada pelas asperidades e pelas partículas de desgaste formadas entre a superfície e o contra corpo. Uma significante diminuição no desgaste foi observada em todas as amostras tratadas por DL, com uma redução de uma ordem de grandeza quando comparado a amostra sem tratamento.

Aluminum - Silicon alloys are recognized as appropriate materials for high performance cast components used in transportation powertrain applications. A combination of excellent wear resistance, good thermal conductivity and low density make these materials good candidates for engine bore applications. It is well accepted that the tribological properties of these alloys are dictated by the presence of hard eutectic silicon particles and their distribution in the soft aluminum matrix. Three near-eutectic aluminum-silicon engine bore alloys manufactured by different processing routes such as sand casting, chill casting and spray compaction were investigated to determine the influence of solidification on evolution of microstructure of these alloys and to establish correlation of microstructure with tribological properties. The spatial distribution of the silicon particles in aluminum matrix is analyzed using various image analysis techniques and contact distribution studies. The chill cast alloy shows large columnar primary aluminum dendrites interspersed with coarse silicon particles. The sand cast and spray compacted alloys show better spatial distribution of refined silicon particles. Microstructures generated under different solidification modes are found to have varying morphologies. The crystallographic orientations of the dendritic and eutectic aluminum as well as that of the eutectic silicon were studied using electron backscatter diffraction (EBSD). The eutectic silicon nucleating in chill cast alloy is found to exhibit strong orientation relationship with the aluminum matrix. The crystallographic orientation relationship shows that the solidification modes of the eutectics in these three alloys are different, from alloy to alloy, due to their different solidification rates and due to the addition of grain refiners and modifiers. The hardness values of the aluminum matrix and silicon particles of these alloys were found using nanoindentation and micro indentation tests. Preliminary wear studies were carried out on etched and unetched test alloys in dry reciprocating sliding. The results show that of the three test alloys, the alloy in which eutectic regions nucleate heterogeneously from the primary aluminum dendrites gives the best wear resistance and the highest hardness. The very low friction coefficient recorded for the etched alloys is accounted for by the insitu formation of a thin sheet of tribofilm on the protruding silicon particles. The physical and chemical natures of this protective film are being investigated.

[pt] Neste trabalho estudamos filmes depositados por três organosilícios em forma líquida pelo método de deposição química na fase vapor assistido por plasma (PECVD) sobre chapas de aço inoxidável 316L e lâminas de silício cristalino <100>. Os líquidos empregados foram o Hexametidissilazano (HMDSN), Hexametidissiloxano (HMDSO) e Hexametildissilano (HMDS). Determinamos as propriedades estruturais, mecânicas e tribológicas dos filmes crescidos, e a viabilidade do seu uso como revestimento protetor. Foram depositados dois conjuntos de amostras para cada líquido, o primeiro a 200C e o segundo 300oC. Em cada um dos conjuntos, a tensão de autopolarização no crescimento foi variada indo de -150V até -450V. Tentou-se caracterizar filmes crescidos a temperatura ambiente, porém não obtivemos êxito, pois delaminavam. Os filmes foram caracterizados por técnicas de perfilometria, onde determinamos que os filmes crescidos com temperaturas de 200C tiveram a maior taxa de deposição. Estes filmes para todos os líquidos possuem uma tensão interna entre 1 e 2 GPa. Os filmes foram analisados também por espectroscopia de fotoelétrons induzidos por raios-x (XPS), espectroscopia de absorção no infravermelho e espectroscopia de emissão ótica (GDOES) onde identificamos as concentrações atômicas e as ligações químicas presentes nos filmes. Com a espectroscopia Raman observamos que os filmes têm presença de carbonos com hibridização sp2. Os filmes sintetizados têm um forte caráter polimérico, e para os crescidos com tensões de autopolarização maiores que -250V, observamos a presença das bandas D e G características de filmes de carbono amorfo. As análises feitas por nanoindentação determinou que os filmes tinham dureza entre 18 e 21 GPa. A microscopia de força atômica evidenciou que os filmes têm uma rugosidade rms em torno de 0,3nm. Medida de tribologia mostraram que os filmes têm um coeficiente de atrito de 0,25. Após as medidas de tribologia, foram feitas imagens de perfilometria para determinar o desgaste. Os filmes se mostraram resistentes, com a menor taxa de 7nm/min quando submetido a uma força de 0,3 Newtons e como contra corpo uma esfera de aço inoxidável (AISI302), e após as medidas os filmes não delaminaram. Com relação ao envelhecimento do filme, alguns foram sintetizados a mais de 4 anos, e continuam bem aderidos tanto sobre o substrato de aço, como o de silício. Verificamos também a viabilidade do uso do hexametildissílazano (HMDSN) como camada adesiva para a deposição de filmes de carbono amorfo hidrogenado sobre chapas de aço inoxidável com sucesso. Fizemos também a deposição de um filme depositado a partir do hexametildissiloxano (HMDSO) sobre um parafuso de aço inoxidável para verificar a viabilidade para deposições sobre materiais com geometrias diferentes, com sucesso, o filme bem aderido em sua superfície. / [en] In this work, we study films deposited by three organosilanes in liquid phase by the plasma deposition method (PECVD) on 316L stainless steel plates and crystalline silicon slides <100>. The liquids employed were Hexamethyldisilazane (HMDSN), Hexamethyldisiloxane (HMDSO) and Hexamethyldisilane (HMDS). We determined the structural, mechanical and tribological properties of grown films, and the feasibility of their use as a protective coating. Two sets of samples were deposited for each liquid, the first at 200C and the second at 300C. In each set, the bias at the growth was varied ranging from -150V to -450V. Attempts were made to characterize films grown at room temperature, but we did not succeed because they delaminated. The films were characterized by profilometry techniques, where we determined that the films grown with temperatures of 200oC had the highest deposition rate. The films were also analyzed by x-ray photoelectron spectroscopy (XPS), infrared absorption spectroscopy (FTIR) and glow discharge optical emission spectroscopy (GDOES), where we identified the atomic concentrations and the chemical bonds present in the films. With the Raman spectroscopy we observed that the films have presence of carbons with hybridization sp2. The films synthesized have a strong polymeric character, and for those grown with bias higher than -250V, we observed the presence of D- and G- bands that are characteristics of amorphous carbon films. Analysis by nanoindentation determined that the films had a hardness between 18 and 21 GPa. Atomic force microscopy showed that the films have a roughness RMS around 0.3nm. Measurement of tribology showed that the films have a coefficient of friction of 0.25. After the tribology measurements, profilometry images were made to determine the wear. The films were resistant, with the lowest rate of 7 nm/min when subjected to a force of 0.3 Newtons and as against a body of stainless steel (AISI302), and after the measurements the films did not delaminate. Regarding the aging of the film, some were synthesized for more than 4 years, and remain well adhered both on the steel substrate and silicon. We also verified the feasibility of using hexamethyldisilazane (HMDSN) as an adhesive layer for the deposition of hydrogenated amorphous carbon films on stainless steel substrate successfully. We also deposited a film from the hexamethyldisiloxane (HMDSO) on a stainless steel screw to verify the feasibility for deposition on materials with different geometries, successfully, the film was well adhered on its surface.