"The CHTE surface hardening simulation tools, CarboNitrideTool© and CarbTool© have been enhanced to improve the accuracy of the simulation and to predict the microstructure and microhardness profiles after the heat treatment process. These tools can be used for the prediction of both gas and low pressure carburizing processes. The steel alloys in the data base include 10XX, 48XX, 51XX, 86XX, 93XX and Pyrowear 53. They have been used by CHTE members to design efficient carburizing cycles to maximum the profit by controlling the cost and time. In the current software, the model has successfully predicted the carbon concentration profiles for gas carburizing process and many low pressure carburizing processes. In some case, the simulation toll may not work well with the low pressure carburizing process, especially with AISI 9310 alloy. In the previous simulation, a constant carbon flux boundary condition was used. However, it has been experimentally proven that the flux is a function of time. The high carbon potential may cause soot and carbides at the outer edge. The soot and carbides will impede the diffusion of carbon during the low pressure carburizing process. The constant carbon flux cannot be appropriately used as the boundary condition. An improved model for the process is proposed. In the modeling, carbon potential and mass transfer coefficient are calculated and used as the boundary condition. CarbonitrideToolⒸ has been developed for the prediction of both carbon and nitrogen profiles for carbonitriding process. The microstructure and hardness profile is also needed by the industry. The nitrogen is an austenite stabilizer which result in high amount of retained austenite (RA). RA plays important role in the hardness. The model has been developed to predict the Martensite start temperature (Ms) which can be used for RA prediction. Mixture rule is used then to predict the hardness profiles. Experiments has been conducted to verify the simulation. The hardness profile is also predicted for tempered carburized alloys. Hollomon-Jaffe equation was used. A matrix of tempering experiments are conducted to study the Hollomon Jaffe parameter for AISI 8620 and AISI 9310 alloy. Constant C value is calculated with a new mathematical method. With the calculation result, the hardness profile can be predicted with input of tempering time and temperature. Case depth and surface hardness are important properties for carburized steel that must be well controlled. The traditional testing is usually destructive. Samples are sectioned and measured by either OES or microhardness tester. It is time consuming and can only be applied on sampled parts. The heat treating industry needs a physics based, verified simulation tool for surface hardening processes to accurately predict concentration profiles, microstructure and microhardness profiles. There is also a need for non-destructive measurement tool to accurately determine the surface hardness and case depth. Magnetic Barkhausen Noise (MBN) is one of the promising way to test the case depth and hardness. MBN measures the pulses generating by the interaction between magnetic domain walls in the ferromagnetic material and the pinning sites such as carbides, impurities and dislocation. These signals are analyzed to evaluate the properties of the carburized steel. "

Le traitement de carbonitruration est aujourd'hui un procédé très répandu pour augmenter la résistance mécanique des pièces en acier. Ce type de solution a fait ses preuves dans le cadre de pièces massives, mais l'oxydation interne des couches enrichies reste une limitation conséquente du traitement à pression atmosphérique.C'est dans cette optique scientifique que s'inscrit une partie de cette étude visant le développement d'un traitement de carbonitruration à basse pression, en vue d'une application industrielle. Les nombreuses investigations expérimentales réalisées sur la nuance 16MnCr5 ont permis le développement et la mise au point de deux cycles répondant à deux critères de profondeur de traitement : 0.25 — 0.4 mm et 0.7 — 1.2 mm. Les observations métallurgiques ne révèlent aucune forme de précipitation, ce qui n'est pas le cas lorsque que le traitement est appliqué à une nuance métallurgique plus fortement alliée (Fe - 0.18 %C - 3.12 % Cr - 0.7 %V -0.45 %W).D'un point de vue simulation, les outils de calculs thermodynamiques confirment et clarifient les phénomènes de précipitations observés. L'acier plus fortement allié (qui contient initialement des carbures de vanadium de type MC) présente des carbures de types M23C6 et M7C3 ainsi que des carbonitrures de types M (C, N). En complément à la détermination des phases en présence et de leur composition, une modélisation de la diffusion du carbone et de l'azote est proposée. Le modèle utilise des conditions aux limites déterminées expérimentalement, des coefficients de diffusion du carbone et de l'azote interdépendants issus de la littérature. La cinétique de refroidissement au cours de la trempe est déterminée pour alimenter le modèle de calcul de transformation de phases et simuler le profil de dureté. Le couplage des modèles développés donne des résultats très proches des profils de carbone, azote et duretés mesurés expérimentalement.Une autre partie du travail propose l'intégration du traitement de carbonitruration à basse pression au procédé de mise en œuvre MIM (Moulage par Injection de poudres Métalliques) permettant la réalisation des composants de formes complexes. Les pièces « MIM » obtenues par l'exploitation du feedstock commercial PolyMIM 16MnCr5 intégrant un système de liant soluble à l'eau présentent 10 % de porosité. Les résultats métallurgiques observés sur les pièces MIM carbonitrurées consécutivement au palier de frittage sont identiques à ceux observés sur des pièces massives. La comparaison des profils de diffusion en carbone et azote entre les pièces à 10 et20 % de porosité (obtenu par diminution de la durée du pallier de frittage) montre cependant que le taux de porosité influence la profondeur de traitement. / The carbonitriding treatment is now a widely accepted industrial process to improve the strength of treated steel parts. This type of solution has been proven in the case of massive parts, but internal oxidation of enriched layers remains a significant drawback of the treatment at atmospheric pressure.It is against this scientific backdrop that this project seeks to develop a carbonitriding treatment at low pressure for industrial application. Numerous experimental investigations carried out on the 16MnCr5 steel grade allowed the development of cycles answering two criteria of depth treatment: 0.25 - 0.4 mm 0.7 - 1.2 mm. Metallurgical observations show no form of precipitation, which however is no longer the case when the treatment is applied to a more highly alloyed steel grade (Fe - 0.18% C - 3.12% Cr - 0.7% V -0.45% W).From a simulation point of view, thermodynamic calculations confirm and clarify the precipitation phenomena observed. The more highly alloyed steel (which initially contains vanadium rich carbides of MC type) exhibits carbides of M23C6 and M7C3 type, and carbonitrides of M (C, N) type. To complement the determination of present phases and their composition, it is proposed that the diffusion of carbon and nitrogen be modeled. The model uses experimentally determined boundary conditions, and interdependent nitrogen and carbon taken from the literature. The kinetics of cooling during the quenching is determined to supply the calculation model of phase transformations and simulate the hardness profile. The coupling of developed models gives carbon, nitrogen and hardness profiles very similar to experimentally measured ones.The work also proposes the integration of the low-pressure carbonitriding treatment to the MIM (Metal Injection Moulding) process, allowing the production of complex shapes components. MIM parts obtained from the exploitation of the trade PolyMIM 16MnCr5 feedstock integrating a water-soluble binder system present 10% of porosity. Metallurgical results observed on MIM parts, carbonitrided consecutively to the sintering step are similar to those observed on massive wrought parts. Comparison of carbon and nitrogen profiles of carbonitrided MIM parts containing 10 and 20 % of porosity (obtained by reducing the length of the bearing sintering) shows that the porosity level influences the case depth of MIM parts.

A fragilização por hidrogênio é uma potencial causa de falha em diversos componentes industriais. Este tipo de fragilização ocorre principalmente em aços ao carbono e também em aços inoxidáveis martensíticos, que apresentam alta resistência mecânica. Neste trabalho, avaliou-se a influência das temperaturas de revenimento de 300 ºC, 400 ºC e 500 ºC na fragilização por hidrogênio do aço ABNT 10B22-Modificado, após o processo de carbonitretação, o qual é muito utilizado na fabricação de parafusos e fixadores. Foram confeccionados corpos de prova convencionais segundo a Norma NACE TM 177-90 e também foram usados parafusos M4 X50 fabricados conforme a Norma DIN 13 para realização dos ensaios. As amostras foram submetidas a três níveis de introdução forçada de hidrogênio (10mA/cm2, 20mA/cm2 e 30mA/cm2) por controle galvanostático, para as diferentes temperaturas de revenimento. Para efeito comparativo, para cada temperatura de revenido foram produzidas amostras isentas de hidrogênio, caracterizando a condição inicial do material. Todas as amostras foram submetidas ao ensaio de tração com baixa taxa de deformação. Os corpos de prova convencionais foram também ensaiados em tração com carregamento simultâneo de hidrogênio, enquanto os parafusos foram submetidos ao ensaio de torque de fragilização com carregamento prévio. Foram caracterizados os micromecanismos de fratura em todas as condições das amostras confeccionadas. Os resultados obtidos evidenciaram que para menores temperaturas de revenimento as amostras carregadas com hidrogênio apresentaram uma maior perda das propriedades mecânicas como resistência à tração, tenacidade e alongamento quando comparadas a condição inicial, sendo que a geometria do parafuso foi mais propensa aos efeitos deletérios do hidrogênio que os corpos de prova convencionais. O micromecanismo de fratura na camada carbonitretada foi predominantemente intergranular nas amostras carregadas com hidrogênio e o núcleo apresentou coalescimento de microcavidades na maioria dos casos, com microcavidades rasas nas amostras carregadas com hidrogênio. / Hydrogen embrittlement is a potential cause of failure in various industrial components. This type of embrittlement occurs mainly in carbon steels and in martensitic stainless steels, which have high mechanical strength. In this study, it was evaluated the influence of the tempering temperatures of 300 ºC, 400 ºC and 500 ºC on the hydrogen embrittlement effect, for the ABNT 10B22-modified steel, after the process of carbonitriding, which is widely used in the manufacture of screws and fasteners. The specimens were machined according to the NACE TM 177-90 standard and were also employed as specimens in the tests, screws M4 X50 manufactured according to the DIN 13 standard. The samples were subjected to three levels of hydrogen charge (10mA/cm2, 20mA/cm2 and 30mA/cm2) by galvanostatic control for the different tempering temperatures. For comparison, each tempering temperature sample was produced free of hydrogen, characterizing the initial condition of the material. All samples were subjected to slow strain rate tensile test. The specimens were also analyzed in conventional tensile tests with simultaneous charging of hydrogen, while the screws were subjected to the embrittlement torque testing with precharged specimens. Micromechanisms of fracture were characterized in all conditions for each of the samples. The results showed that lower tempering temperatures caused greater losses of mechanical properties such as tensile strength, elongation and toughness for the hydrogen charged samples when compared to the initial condition, and the geometry of the screw was more prone to the deleterious effects of hydrogen that conventional standardized specimens. The case fracture micromechanism was predominantly intergranular in samples charged with hydrogen and the core showed coalescence of microcavities micromechanism, in most cases, with shallow microvoids in the samples charged with hydrogen.

A fragilização por hidrogênio é uma potencial causa de falha em diversos componentes industriais. Este tipo de fragilização ocorre principalmente em aços ao carbono e também em aços inoxidáveis martensíticos, que apresentam alta resistência mecânica. Neste trabalho, avaliou-se a influência das temperaturas de revenimento de 300 ºC, 400 ºC e 500 ºC na fragilização por hidrogênio do aço ABNT 10B22-Modificado, após o processo de carbonitretação, o qual é muito utilizado na fabricação de parafusos e fixadores. Foram confeccionados corpos de prova convencionais segundo a Norma NACE TM 177-90 e também foram usados parafusos M4 X50 fabricados conforme a Norma DIN 13 para realização dos ensaios. As amostras foram submetidas a três níveis de introdução forçada de hidrogênio (10mA/cm2, 20mA/cm2 e 30mA/cm2) por controle galvanostático, para as diferentes temperaturas de revenimento. Para efeito comparativo, para cada temperatura de revenido foram produzidas amostras isentas de hidrogênio, caracterizando a condição inicial do material. Todas as amostras foram submetidas ao ensaio de tração com baixa taxa de deformação. Os corpos de prova convencionais foram também ensaiados em tração com carregamento simultâneo de hidrogênio, enquanto os parafusos foram submetidos ao ensaio de torque de fragilização com carregamento prévio. Foram caracterizados os micromecanismos de fratura em todas as condições das amostras confeccionadas. Os resultados obtidos evidenciaram que para menores temperaturas de revenimento as amostras carregadas com hidrogênio apresentaram uma maior perda das propriedades mecânicas como resistência à tração, tenacidade e alongamento quando comparadas a condição inicial, sendo que a geometria do parafuso foi mais propensa aos efeitos deletérios do hidrogênio que os corpos de prova convencionais. O micromecanismo de fratura na camada carbonitretada foi predominantemente intergranular nas amostras carregadas com hidrogênio e o núcleo apresentou coalescimento de microcavidades na maioria dos casos, com microcavidades rasas nas amostras carregadas com hidrogênio. / Hydrogen embrittlement is a potential cause of failure in various industrial components. This type of embrittlement occurs mainly in carbon steels and in martensitic stainless steels, which have high mechanical strength. In this study, it was evaluated the influence of the tempering temperatures of 300 ºC, 400 ºC and 500 ºC on the hydrogen embrittlement effect, for the ABNT 10B22-modified steel, after the process of carbonitriding, which is widely used in the manufacture of screws and fasteners. The specimens were machined according to the NACE TM 177-90 standard and were also employed as specimens in the tests, screws M4 X50 manufactured according to the DIN 13 standard. The samples were subjected to three levels of hydrogen charge (10mA/cm2, 20mA/cm2 and 30mA/cm2) by galvanostatic control for the different tempering temperatures. For comparison, each tempering temperature sample was produced free of hydrogen, characterizing the initial condition of the material. All samples were subjected to slow strain rate tensile test. The specimens were also analyzed in conventional tensile tests with simultaneous charging of hydrogen, while the screws were subjected to the embrittlement torque testing with precharged specimens. Micromechanisms of fracture were characterized in all conditions for each of the samples. The results showed that lower tempering temperatures caused greater losses of mechanical properties such as tensile strength, elongation and toughness for the hydrogen charged samples when compared to the initial condition, and the geometry of the screw was more prone to the deleterious effects of hydrogen that conventional standardized specimens. The case fracture micromechanism was predominantly intergranular in samples charged with hydrogen and the core showed coalescence of microcavities micromechanism, in most cases, with shallow microvoids in the samples charged with hydrogen.

A fragilização por hidrogênio é uma potencial causa de falha em diversos componentes industriais. Este tipo de fragilização ocorre principalmente em aços ao carbono e também em aços inoxidáveis martensíticos, que apresentam alta resistência mecânica. Neste trabalho, avaliou-se a influência das temperaturas de revenimento de 300 ºC, 400 ºC e 500 ºC na fragilização por hidrogênio do aço ABNT 10B22-Modificado, após o processo de carbonitretação, o qual é muito utilizado na fabricação de parafusos e fixadores. Foram confeccionados corpos de prova convencionais segundo a Norma NACE TM 177-90 e também foram usados parafusos M4 X50 fabricados conforme a Norma DIN 13 para realização dos ensaios. As amostras foram submetidas a três níveis de introdução forçada de hidrogênio (10mA/cm2, 20mA/cm2 e 30mA/cm2) por controle galvanostático, para as diferentes temperaturas de revenimento. Para efeito comparativo, para cada temperatura de revenido foram produzidas amostras isentas de hidrogênio, caracterizando a condição inicial do material. Todas as amostras foram submetidas ao ensaio de tração com baixa taxa de deformação. Os corpos de prova convencionais foram também ensaiados em tração com carregamento simultâneo de hidrogênio, enquanto os parafusos foram submetidos ao ensaio de torque de fragilização com carregamento prévio. Foram caracterizados os micromecanismos de fratura em todas as condições das amostras confeccionadas. Os resultados obtidos evidenciaram que para menores temperaturas de revenimento as amostras carregadas com hidrogênio apresentaram uma maior perda das propriedades mecânicas como resistência à tração, tenacidade e alongamento quando comparadas a condição inicial, sendo que a geometria do parafuso foi mais propensa aos efeitos deletérios do hidrogênio que os corpos de prova convencionais. O micromecanismo de fratura na camada carbonitretada foi predominantemente intergranular nas amostras carregadas com hidrogênio e o núcleo apresentou coalescimento de microcavidades na maioria dos casos, com microcavidades rasas nas amostras carregadas com hidrogênio. / Hydrogen embrittlement is a potential cause of failure in various industrial components. This type of embrittlement occurs mainly in carbon steels and in martensitic stainless steels, which have high mechanical strength. In this study, it was evaluated the influence of the tempering temperatures of 300 ºC, 400 ºC and 500 ºC on the hydrogen embrittlement effect, for the ABNT 10B22-modified steel, after the process of carbonitriding, which is widely used in the manufacture of screws and fasteners. The specimens were machined according to the NACE TM 177-90 standard and were also employed as specimens in the tests, screws M4 X50 manufactured according to the DIN 13 standard. The samples were subjected to three levels of hydrogen charge (10mA/cm2, 20mA/cm2 and 30mA/cm2) by galvanostatic control for the different tempering temperatures. For comparison, each tempering temperature sample was produced free of hydrogen, characterizing the initial condition of the material. All samples were subjected to slow strain rate tensile test. The specimens were also analyzed in conventional tensile tests with simultaneous charging of hydrogen, while the screws were subjected to the embrittlement torque testing with precharged specimens. Micromechanisms of fracture were characterized in all conditions for each of the samples. The results showed that lower tempering temperatures caused greater losses of mechanical properties such as tensile strength, elongation and toughness for the hydrogen charged samples when compared to the initial condition, and the geometry of the screw was more prone to the deleterious effects of hydrogen that conventional standardized specimens. The case fracture micromechanism was predominantly intergranular in samples charged with hydrogen and the core showed coalescence of microcavities micromechanism, in most cases, with shallow microvoids in the samples charged with hydrogen.

The main purpose of this thesis work was to halve the cycle time of a grinding process of the groove of carbonitrided ball bearings rings. The study was conducted as a Six Sigma project at SKF in Bari, Italy. Reaching the goal was important for the company as it meant avoiding the purchase of another grinding machine. The groove grinding process on carbonitrided rings features double the cycle time than the same process on through hardened rings and halving it was required to fulfill the volumes demanded. The Six Sigma methodology was applied through the implementation of DMAIC. The analysis of the problems and identification of areas for improvement were carried out deploying different tools such as an Ishikawa diagram, Hypothesis Testing and Statistical Process Control. The outcome of this was the need to optimize the carbonitriding process minimizing the depth of the layer without enlarged carbides in order to render the design of the part easier to machine and subsequently find the process parameters for the groove grinding yielding a cycle time of six seconds. Many trials were conducted with the supplier of carbonitriding, until the carbon and ammonia potentials were set at levels resulting in a depth of the layer allowing the change of the design. An optimizing DOE was instead performed for the grinding process which highlighted the parameters settings yielding the target cycle time. Finally actions and controls to perform in order to maintain the gains were defined.

Visando-se determinar as temperaturas mais adequadas de nitretação e carbonitretação por plasma dos aços inoxidáveis austenítico AISI 316L, ferrítico AISI 409 e super duplex ASTM A890 Gr 5A e suas influências nas resistências ao desgaste e à corrosão, amostras desses aços foram tratadas a 400, 450 e 500°C, e submetidas a ensaios micrográficos, de raios X, ensaios microabrasivos e de corrosão. Todas as temperaturas de tratamentos utilizadas nos vários aços estudados produziram camadas com grande regularidade, que tiveram suas espessuras e durezas aumentadas com o aumento da temperatura de tratamento. Em todos os casos, ocorreu um grande aumento nas resistências ao desgaste microabrasivo das amostras nitretadas ou carbonitretadas, em comparação com o substrato, comprovando a efetividade da fase \"S\", produzida nas temperaturas mais baixas, no aumento das durezas e resistências ao desgaste. No caso das amostras tratadas em temperaturas mais elevadas, o nitreto de cromo foi o responsável principal pelo aumento dessa resistência. Verificou-se por meio dos resultados das curvas de polarização anódicas das camadas nitretadas e carbonitretadas a 400°C que, para os três tipos de aços em estudo, tais camadas apresentaram comportamentos semelhantes e superiores aos dos substratos, devido a formação de austenita ou ferrita expandidas. No caso das temperaturas de tratamentos de 450 e 500°C, as amostras carbonitretadas apresentaram desempenho superior ao das nitretadas e, próximos aos dos substratos, não tendo ocorrido degradação dessa propriedade. Os tratamentos de nitretação e carbonitretação por plasma, realizados nas temperaturas adequadas definidas no presente trabalho para os principais tipos de aços inoxidáveis, produziram camadas com elevadas durezas e resistências ao desgaste, sem perdas nas características de corrosão, que inclusive melhoraram em alguns casos, permitem a ampliação do uso dos aços inoxidáveis para situações que requeiram aquelas propriedades. / Aiming to determine the most appropriate temperatures of plasma and carbonitriding of the AISI 316L austenitic stainless steel, AISI 409 stainless steel and ASTM A890 Gr5A super duplex steel and their influence corrosion and wear resistances of those steel samples, they were treated 450 and 500°C, and submitted to micrography analyses, X-ray diffraction, abrasive wear and corrosion tests. All treatment temperatures used in the several studied steels produced layers with great regularity, which increased their thickness and hardness with the increase of the treatment temperature. In all the cases, a great increase occurred in the micro-abrasivive resistance of the nitrided and carbonitrided samples, in comparison with the substrate, proving the effectiveness of the \"S\" phase, produced in the temperatures, in the increase of the hardness and wear resistances. In the the samples treated at higher temperatures, the chromium nitride was the responsible one for the increase in the wear resistance. It was verified through the results of the potenciodinâmicos corrosion the nitrided and carbonitrided layers at 400°C, that for the three types of stee study, such layers presented similar and superior behaviors to that of the substrate, due to austenite or expanded ferrite formation. In the case of the treatment temperatures of 450 and 500°C, the carbonitrided samples presented s performance to the nitrided one and similar performance to the substrates s without the occurrence of any degradation of that property. The plasma nitriding and plasma carbonitriding treatments, carried out in the temperatures defined in the present work, for the principal types of stainless to produce layers with high hardness and wear resistances, without losses corrosion characteristics, which even got better in some cases, allow to expand the use of the stainless steels in situations where those properties are required.

Le développement de matériaux d'ingénierie combinant ténacité et résistance à l'usure reste encore un défi. Dans le but de contribuer à ce domaine, cette thèse présente une étude de la carbonitruration des aciers 16NiCrMo13 et 23MnCrMo5. L'évolution cinétique des atmosphères à base d'hydrocarbures et d'ammoniac est étudiée numériquement, ainsi que le comportement local à l'équilibre et la cinétique de diffusion pour l'obtention de profils d'enrichissement des alliages traités. Les simulations sont confrontées à des mesures par chromatographie en phase gazeuse des produits de pyrolyse de l'acétylène et de décomposition de l'ammoniac, et aux réponses métallurgiques, par l'évaluation des profils de diffusion, des filiations de dureté et par l'identification des précipités formés par microscopie électronique en transmission. La dureté obtenue après trempe et traitement cryogénique évolue selon la racine carrée de la teneur en interstitiels en solution solide simulée à partir de la composition locale en utilisant des mesures des profils chimiques en carbone et en azote. Après revenu, les zones enrichies en azote montrent une tenue en dureté supérieure à celles obtenues avec la même teneur totale en carbone en solution, ce qui a été attribué après observation par microscopie électronique en transmission à une fine précipitation de nitrures de fer lors de cette dernière étape de traitement. Le bilan de matière des produits de pyrolyse montre que les principales espèces non détectées sont des radicaux fortement carbonés qui peuvent aussi donner lieu à la formation d'hydrocarbures polycycliques de haut poids moléculaire dans les zones froides du réacteur. À la pression atmosphérique et à basse pression l'établissement de conditions d'enrichissement en carbone à concentration constante est possible en utilisant de faibles pressions partielles d'acétylène dilué dans l'azote. La conversion atteinte par la pyrolyse de ce précurseur est pourtant importante à la température de traitement compte tenu du temps de séjour caractéristique du réacteur employé à la pression atmosphérique. La cinétique de décomposition de l'ammoniac étant beaucoup plus lente que celle des hydrocarbures légers, il a été possible de quantifier la vitesse de décomposition de cette espèce par unité de surface métallique exposée pendant la durée d'un traitement / The development of engineering materials combining both toughness and wear resistance is still a challenge. Aiming to contribute to this field of study, this thesis presents a study of the carbonitriding process of alloys 16NiCrMo13 and 23MnCrMo5. Kinetics of hydrocarbon- and ammonia-based atmospheres, as well as local equilibrium and diffusion kinetics for achieving the enrichment profiles, are studied by numerical simulation. These simulations are compared to chromatography measurements of gas phase pyrolysis products of acetylene and ammonia decomposition, and with metallurgical responses, where the comparison is made with evaluated diffusion profiles, hardness measurements and the identification of precipitates by transmission electron microscopy. Hardness after quench and cryogenic treatment depends on the square root of total solid solution interstitial content simulated by using local carbon and nitrogen compositions obtained experimentally. After tempering, the regions enriched in nitrogen show better hardness stability than those with same total carbon interstitial content, what was linked to a fine precipitation of iron nitrides observed by transmission electron microscopy. Mole balance of pyrolysis products show that the main non-detected species are high-carbon radicals, which may also lead to the formation of polycyclic aromatic hydrocarbons of high molecular weight at the reactor outlet. At both atmospheric and reduced pressures, constant concentration enrichment boundary conditions were established by using low partial pressures of acetylene diluted in nitrogen. Pyrolysis of this precursor attains high conversion rates at treatment conditions given the important residence time of the atmospheric pressure reactor. Ammonia decomposition kinetics being much slower than that of low molecular weight hydrocarbons, it was possible to identify the decomposition rate of this species over a metallic sample during a treatment

Made available in DSpace on 2016-12-08T17:19:20Z (GMT). No. of bitstreams: 1 0- Capa.pdf: 52849 bytes, checksum: 052f0059aa665dd6426fbaf7c75b0a07 (MD5) Previous issue date: 2005-12-16 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The objective of this dissertation is to study the friction focusing in the forces and energies needed to initiate the movement and keep it. The surfaces textures role is analyzed in roughness, r.m.s slope and fractal dimension of the surfaces profiles. This study showed that the surface profile r.m.s. slope is the main parameter to obtain the fraction coefficient figures. This study showed that it is essential to qualify the contact before to proceed with the quantitative calculation. The best parameter found to qualify the contact behavior is the Mikic plasticity index, which is compounded by the r.m.s. slope, the reduced elasticity modulus and the Vickers hardness of the materials in contact. It were prepared Ti6Al4V samples with three textures: sand blasting, shoot pinning and polished in order to verify the role of the textures regarding friction. A half of the samples were treated via plasma carbonitriding where surfaces free of micro cracks and with a relevant gain on the surface hardness were obtained. All the textures combinations were tested regarding their friction coefficients before and after the treatment. The treated samples shown similar or lightly high friction coefficients than the non treated samples, however after the friction test it was noticed that the treated samples presented less wear than the non treated samples. / O objetivo desta dissertação é estudar o atrito com foco nas forças e energias necessárias para iniciar o movimento e mantê-lo. A influência das texturas das superfícies em contato no coeficiente de atrito é analisada em rugosidade, inclinação média e dimensão fractal dos perfis das superfícies. O estudo mostrou que a inclinação média dos perfis das superfícies é o principal parâmetro relacionado ao coeficiente de atrito. O estudo mostra que é essencial qualificar o contato antes de proceder aos cálculos do coeficiente de atrito. O parâmetro que se mostrou eficiente para qualificar o regime de deformação do contato é o índice de plasticidade de Mikic, o qual é formado pela inclinação média e duas propriedades dos materiais: módulo de elasticidade reduzido e as durezas Vickers. Foram preparadas amostras de Ti6Al4V com texturas polidas, jateadas e jateadas com esferas de aço (shoot pinning) para verificar a influência da geometria das superfícies em contato no coeficiente de atrito. Metade das amostras foram carbonitretadas por plasma onde se obteve superfícies sem trincas e com ganho significativo na dureza de superfície. Todas as combinações de textura foram testadas em relação ao coeficiente de atrito antes e depois do tratamento. As amostras tratadas apresentaram coeficiente de atrito similar ou ligeiramente maior que as não tratadas, porém após os testes observou-se que as amostras tratadas apresentaram menor desgaste.

Visando-se determinar as temperaturas mais adequadas de nitretação e carbonitretação por plasma dos aços inoxidáveis austenítico AISI 316L, ferrítico AISI 409 e super duplex ASTM A890 Gr 5A e suas influências nas resistências ao desgaste e à corrosão, amostras desses aços foram tratadas a 400, 450 e 500°C, e submetidas a ensaios micrográficos, de raios X, ensaios microabrasivos e de corrosão. Todas as temperaturas de tratamentos utilizadas nos vários aços estudados produziram camadas com grande regularidade, que tiveram suas espessuras e durezas aumentadas com o aumento da temperatura de tratamento. Em todos os casos, ocorreu um grande aumento nas resistências ao desgaste microabrasivo das amostras nitretadas ou carbonitretadas, em comparação com o substrato, comprovando a efetividade da fase \"S\", produzida nas temperaturas mais baixas, no aumento das durezas e resistências ao desgaste. No caso das amostras tratadas em temperaturas mais elevadas, o nitreto de cromo foi o responsável principal pelo aumento dessa resistência. Verificou-se por meio dos resultados das curvas de polarização anódicas das camadas nitretadas e carbonitretadas a 400°C que, para os três tipos de aços em estudo, tais camadas apresentaram comportamentos semelhantes e superiores aos dos substratos, devido a formação de austenita ou ferrita expandidas. No caso das temperaturas de tratamentos de 450 e 500°C, as amostras carbonitretadas apresentaram desempenho superior ao das nitretadas e, próximos aos dos substratos, não tendo ocorrido degradação dessa propriedade. Os tratamentos de nitretação e carbonitretação por plasma, realizados nas temperaturas adequadas definidas no presente trabalho para os principais tipos de aços inoxidáveis, produziram camadas com elevadas durezas e resistências ao desgaste, sem perdas nas características de corrosão, que inclusive melhoraram em alguns casos, permitem a ampliação do uso dos aços inoxidáveis para situações que requeiram aquelas propriedades. / Aiming to determine the most appropriate temperatures of plasma and carbonitriding of the AISI 316L austenitic stainless steel, AISI 409 stainless steel and ASTM A890 Gr5A super duplex steel and their influence corrosion and wear resistances of those steel samples, they were treated 450 and 500°C, and submitted to micrography analyses, X-ray diffraction, abrasive wear and corrosion tests. All treatment temperatures used in the several studied steels produced layers with great regularity, which increased their thickness and hardness with the increase of the treatment temperature. In all the cases, a great increase occurred in the micro-abrasivive resistance of the nitrided and carbonitrided samples, in comparison with the substrate, proving the effectiveness of the \"S\" phase, produced in the temperatures, in the increase of the hardness and wear resistances. In the the samples treated at higher temperatures, the chromium nitride was the responsible one for the increase in the wear resistance. It was verified through the results of the potenciodinâmicos corrosion the nitrided and carbonitrided layers at 400°C, that for the three types of stee study, such layers presented similar and superior behaviors to that of the substrate, due to austenite or expanded ferrite formation. In the case of the treatment temperatures of 450 and 500°C, the carbonitrided samples presented s performance to the nitrided one and similar performance to the substrates s without the occurrence of any degradation of that property. The plasma nitriding and plasma carbonitriding treatments, carried out in the temperatures defined in the present work, for the principal types of stainless to produce layers with high hardness and wear resistances, without losses corrosion characteristics, which even got better in some cases, allow to expand the use of the stainless steels in situations where those properties are required.