Influence of anodizing process on fatigue life of a machined aluminium alloy

In order to investigate the coupled effects of machining and anodizing processes on fatigue life of alloy 7010-T7451, a series of rotating bending fatigue tests were conducted at 60Hz. In the as machined condition, test results showed that fatigue life is surface roughness dependent and that fatigue life decreases with an increase in surface roughness and this effect is found to be more pronounced in high cycle fatigue where major portion of fatigue life is consumed in nucleating the cracks. Effects of pretreatments, like degreasing and pickling employed prior to anodizing, on fatigue life of the given alloy were also studied. Results demonstrated that degreasing showed no change in fatigue life while pickling had negative impact on fatigue life of specimens. The small decrease in fatigue life of anodized specimens as compare to pickled specimens is attributed to brittle and microcracking of the coating. Scanning electron microscopic (SEM) examination revealed multi-site crack initiation for the pickled and anodized specimens. SEM examination showed that pickling solution attacked the grain boundaries and intermetallic inclusions present on the surface resulting in pits formation. These pits are of primary concern with respect to accelerated fatigue crack nucleation and subsequent anodized coating formation

Thermal fatigue analysis of automotive Diesel piston: Experimental procedure and numerical protocol

International audienceA new thermal fatigue rig using High Frequency induction heating is developed to test automotive Diesel engine pistons. An adapted test piston is internally cooled by permanent water flow while its bowl sensitive to thermo-mechanical fatigue is subjected to cyclic induction heating. The temperature is measured in depth by thermocouples and in surface by a thermal infrared camera or a pyrometer. The crack initiation and propagation and the local deformations are provided by optical means. Thermo-mechanical loadings are calibrated by thermal measurements on the piston during engine operation and the entire test is modelled by finite elements. A constitutive model and a fatigue criterion for aluminium alloys are proposed to estimate the piston lifetime under severe cyclic loading. The proposed fatigue bench allows loading the piston in thermal fatigue scheme very similar to that encountered in engine operation conditions. Crack detection is facilitated by numerical modelling that helps to detect the most critical areas and also to reliably estimate the number of cycles for initiate cracks

Application of image analysis for thermal fatigue heat checking investigations

International audienceSurface cracking or heat-checking (HC) is investigated on a hot work tool steel (X38CrMoV5 - AISI H11). Different thermal fatigue (TF) test conditions are examined. A semi-automatic and non-destructive investigation method is developed in order to describe the microscopic crack patterns formed on the oxidized specimen surface. TF experiments are periodically interrupted to observe the specimen’s surface with scanning electron microscopy. Crack patterns are evaluated by image analysis. The density and geometrical properties of HC at different stages are characterised. Topological properties of the crack networks are also investigated

Microstructure and mechanical properties of newly developed low activation martensitic steels

The reference ferritic-martensitic steel of the European Fusion Technology Program, the 10CrMoNbV MANET cast, has been modified by replacing the elements that result in long term residual radioactivity when irradiated under a fusion neutron spectra by others which have shorter activation periods. A base composition of a 9CrWVTa steel has been so defined. Two different compositions of the base alloy have been cast from high purity components, in which the Mn and N contents have been varied. The extracted carbide types and their size distribution have been studied under the electron microscope. The mechanical properties of both compositions have been determined. Both steel compositions have a ductile-brittle transition temperature (DBTT) well below room temperature while their tensile properties are comparable to those of the parent (MANET) steel

A correlation between tribological behavior and crystal structure of cobalt-based hardfacings

WOM 2019 - 22nd International Conference on Wear of Materials, 14-18 April 2019, Hyatt Regency Miami, Miami, FL, USAInternational audienceThis paper deals with the influence of the mechanisms of plasticity on the evolution of the friction coefficient in cobalt-based hardfacings. Particularly depending on the alloying element content and so on the stacking fault energy, plasticity in Co-based alloys may occur through mechanisms involving either perfect dislocations gliding and/or partial dislocation gliding. As the coalescence of stacking faults by partial dislocations promotes the phase transformation of the Co, this study focus on the impact of this phase transformation on the evolution of the friction coefficient.Stellite 21 (Co-27Cr-5Mo-0.25C) hardfacings deposited on a steel substrate by two different processes, namely metal inert gas (MIG) and laser, are studied. The tribological properties are evaluated with a ring on disc tribometer under high load (800 daN) and continuous sliding (5 mm/s) at room and high temperatures (450 °C and 600 °C). The wear volume is characterized by confocal microscope. From micro-hardness measurements and SEM observations the work-hardening and the plastic strain of the Tribological Transformations of Surfaces are identified in relationship with chemical analysis (by EDS). Moreover X-rays diffraction and EBSD reveal the crystal structure evolution.As-deposited Co-based hardfacings have a face-centered cubic (FCC) structure. Meanwhile depending on the process of deposition on the steel substrate, the nominal composition of the Stellite 21 can be modified due to dilution effect. So, the iron content is found to be higher in the MIG hardfacing than in the laser one, leading to different mechanisms of plasticity, respectively by perfect dislocations gliding and by phase transformation (FCC to hexagonal closed-packed (HCP)). Moreover, a significant influence of the phase transformation on the friction coefficient has been evidenced: without phase transformation the cobalt remains in the FCC structure and the friction coefficient is stable during the test, while a decrease of its value occurs during the FCC to HCP phase transformation

Wear mechanisms of hardfaced aeronautical high temperature forging tools

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SIMULATION MULTI-ECHELLE DU COMPORTEMENT MECANIQUE D’UN ALLIAGE DE TITANE TI-6AL-4V:Etude de L’influence de la Taille, la Dispersion Relative et la Texture Cristallographique des Grains

International audienceCe travail consiste à étudier l'effet de la taille, la dispersion et la texture cristallographique des grains sur le comportement mécanique d'un alliage de titane Ti-6Al-4V. L'investigation des champs mécaniques (contraintes et déformations) est effectuée aux différentes échelles, sous chargement quasi-statique monotone de traction. Le modèle de comportement utilisé est développé dans le cadre de l'approche de plasticité cristalline. Douze volumes élémentaires représentatifs (VER) permettant la prise en compte des paramètres stériologiques (taille, dispersion et texture cristallographique) sont construits, puis la simulation du comportement mécanique du Ti-6Al-4V est effectuée en utilisant le modèle de méric-Cailletaud [1] en corporation avec la métode des elements finis. Enfin, l'influence des éléments microstructurales du matériau est analysée. Les résultats montrent que le comportement mécanique macroscopique du Ti-6Al-4V est fortement lié à la texture cristallographique des grains, cette dernière donne à la déformation plastique de l'alliage Ti-6Al-4V un caractère hétérogène ainsi qu'un comportement mécanique macroscopique anisotrope. La taille moyenne des grains influe également sur les propriétés mécaniques du Ti-6Al-4V, en particulier sur la limite d'élasticité; en diminuant la taille moyenne des grains, la limite d'élasticité augmente. Enfin la distribution des tailles des grains influe sur le comportement local du matériau, elle donne aux champs de déformation une hétérogénéité suffisante lorsque la dispersion augmente

SIMULATION MULTI-ECHELLE DU COMPORTEMENT MECANIQUE D’UN ALLIAGE DE TITANE TI-6AL-4V:Etude de L’influence de la Taille, la Dispersion Relative et la Texture Cristallographique des Grains

International audienceCe travail consiste à étudier l'effet de la taille, la dispersion et la texture cristallographique des grains sur le comportement mécanique d'un alliage de titane Ti-6Al-4V. L'investigation des champs mécaniques (contraintes et déformations) est effectuée aux différentes échelles, sous chargement quasi-statique monotone de traction. Le modèle de comportement utilisé est développé dans le cadre de l'approche de plasticité cristalline. Douze volumes élémentaires représentatifs (VER) permettant la prise en compte des paramètres stériologiques (taille, dispersion et texture cristallographique) sont construits, puis la simulation du comportement mécanique du Ti-6Al-4V est effectuée en utilisant le modèle de méric-Cailletaud [1] en corporation avec la métode des elements finis. Enfin, l'influence des éléments microstructurales du matériau est analysée. Les résultats montrent que le comportement mécanique macroscopique du Ti-6Al-4V est fortement lié à la texture cristallographique des grains, cette dernière donne à la déformation plastique de l'alliage Ti-6Al-4V un caractère hétérogène ainsi qu'un comportement mécanique macroscopique anisotrope. La taille moyenne des grains influe également sur les propriétés mécaniques du Ti-6Al-4V, en particulier sur la limite d'élasticité; en diminuant la taille moyenne des grains, la limite d'élasticité augmente. Enfin la distribution des tailles des grains influe sur le comportement local du matériau, elle donne aux champs de déformation une hétérogénéité suffisante lorsque la dispersion augmente

Résultats tribologiques de dépôts obtenus par différentes techniques HVOF, MIG, PTA & LASER

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