High rolling contact fatigue parts are vital for the long service life of fuel pumps. Cummins Fuel Systems are currently using an M2 tool steel for one of the most important roller bearing application in their pumps, namely the cam follower. The future design of the cam follower is a pin-less tappet roller. The wear and fatigue properties of the roller is vital to ensure reliability of the fuel system. M2 tool steel is an expensive material and becomes even more so if diamond like coating (DLC) is needed to decrease the friction coefficients. To cut costs of the fuel pump it might be possible to replace the M2 tool steel with 52100 steel (100Cr6). Competitive methods have proven that carbonitrided 52100 can reach excellent wear and fatigue properties making it a candidate to replace M2 tool steel. How the properties of hardness, toughness and compressive residual stresses are developed in 52100 and how they affect the fatigue and wear resistance has been researched from the literature. A big part of this project was to do an extensive analysis of a roller bearing that was believed to have gone through one of these competitive methods that produce excellent wear and fatigue resistance. The analysis was done with background to the knowledge gathered from the literature. Finally process trials were set up to carbonitride 52100 steel samples. The trials were done to develop a better understanding of how adding carbon together with nitrogen to the surface of 52100 steel will influence the metallurgical parameters that results in good wear and fatigue resistance. From this analysis Cummins hope to create a process recipe that can be used for carbonitriding the cam follower and maybe other components in their fuel systems.

Le tantale est un métal très dense (d = 16,6) et fond à très haute température (2996°C), ce qui en fait un matériau potentiellement utilisable pour des creusets utilisés en pyrochimie. La littérature montre qu'il est possible de renforcer encore ces propriétés anti-corrosion par un traitement de cémentation. En effet, la corrosion intergranulaire du tantale est stoppée par la présence de précipités de Ta2C aux joints de grains. L'obtention du Ta saturé carbone avec Ta2C aux joints de grains en surface (Ta(C) + Ta2C), très pauvre en carbone, demande une bonne compréhension et une maitrise de la cémentation du tantale.La réalisation d'un cycle de cémentation sur des échantillons de tantale provoque l'apparition à la surface du tantale d'une couche de TaC (en surface) et d'une couche de Ta2C sous jacente. Un travail sur la réduction du flux de carbone à la surface du tantale a permis d'étudier les premiers stades de formation des couches de carbures de tantale. Ces conditions particulières de cémentation favorisent la croissance en épitaxie des couches de carbures sur le substrat Ta. Les analyses EBSD ont permis de mettre en évidence les relations cristallographiques entre chaque phase.Lors d'un cycle de cémentation, la croissance des couches de carbures doit être contrôlée du fait que celles-ci soient très riches en carbone. Plusieurs types de paramètres peuvent influer sur la croissance des couches : les paramètres de cycles (temps et température de cémentation) et des paramètres extérieurs aux cycles de cémentation, tels que la surface des échantillons. L'influence de ces paramètres sur la cinétique de croissance des couches a été étudiée. En complément des essais, la simulation numérique avec le logiciel CASTEM© a été utilisée afin d'étudier la diffusion du carbone dans le tantale. Les données expérimentales permettent d’ajuster les variables du modèle comme le coefficient de diffusion du carbone dans le tantale.La réalisation d'un recuit sous vide après cémentation permet d'obtenir en surface des microstructures autres que le TaC. Le recuit fait diffuser le carbone contenu en surface vers le coeur du tantale. Une étude a permis de déterminer les paramètres du traitement de recuit, pour obtenir en surface, au choix : du TaC, ou du Ta2C, ou du Ta(C) + Ta2C. / Tantalum is a very dense metal (d = 16.6) and has a very high melting temperature of 2996°C. This material is particularly required for crucibles used for pyrochemical applications. Early studies show that a carburizing treatment enhances corrosion resistance from liquid metals. Indeed, the intergranular attack of tantalum is stopped by Ta2C precipitates, which occupy the grain boundary regions. The production of the carbon saturated tantalum with Ta2C precipitates requires a good understanding of tantalum carburizing.A carburizing treatment on tantalum sample causes the emergence of a TaC layer on surface and Ta2C layer just below. A reduction of carbon flow has enabled the study of the first steps of tantalum carbides formation. This specific condition of carburizing leads to an epitaxic growth of carbide layers on tantalum substrate. EBSD analysis highlights the crystallographic relations between each phase.Tantalum carbide layers are highly carbon concentrated. So the growth of carbide layers has to be controlled during the carburizing treatment. Several parameters may affect carbide layers growth : process parameters (time and temperature of carburizing treatment) and external parameters such as the reactive surface of the samples. The influence of these parameters on tantalum carbide growth kinetics has been studied. In addition, the diffusion of carbon in tantalum has been modeled with CASTEM© software. Experimental data are used to compute parameters of the model, such as carbon diffusion coefficient in tantalum.Other microstructures than TaC can be obtained on surface by applying an annealing treatment after carburizing. With this treatment, the carbon contained on surface diffuses to the bulk of the metal. Annealing treatment parameters have been determined to get on surface TaC, or Ta2C, or carbon saturated tantalum with Ta2C precipitates.