The Ti-6Al-4V alloy is widely used in aerospace applications for its excellent mechanical properties; however, it presents low wear resistance. It is often coated with a cermet using high-velocity oxygen fuel (HVOF) spraying to improve its wear performance. The Cr3C2-NiCr cermet becomes particularly interesting since it is non-carcinogenic, compared to traditional cermet coatings containing tungsten-cobalt compounds. While the improvement in wear resistance of Ti-6Al-4V with this coating has been demonstrated, its impact on the fatigue performance of the alloy remains to be studied. This is precisely the aim of this study, which focuses on the fatigue life of a Cr3C2-25NiCr-coated Ti-6Al-4V alloy. Among the various influencing factors, surface preparation represents a significant source of crack initiation, particularly in the case of sandblasted surfaces. Indeed, the inclusion of fragmented alumina particles can produce stress concentration zones. Thus, laser texturing, which is a method involving the creation of anchoring points through controlled ablation, can be considered today as a less harmful surface preparation technique. The results obtained from cyclic tensile fatigue tests with a stress ratio of 0.1 for these two surface preparation methods, both with and without the coating, are presented in this paper.

Over the past few years, Laser Powder Bed Fusion (L-PBF) has become increasingly popular, as this method enables energy and material savings during the manufacturing process. 3D L-PBF parts, based on computer-designed geometries, are generated layer by layer using laser energy. Since the beginning of these studies several decades ago, significant progress has been made in the understanding of additive manufacturing, particularly with regard to properties, structure and in situ monitoring. However, the scientific manufacturing community has yet to achieve optimal operational reliability. Presently, numerous defects remain a major problem for parts produced by L-PBF. These defects are mainly caused by the movement of the molten material and its rate of solidification within the melt, which is also influenced by the thermal phenomena of the process. In the L-PBF manufacturing process, the main challenge is to control the complex interdependence of these phenomena [1]. The aim of this work is therefore to study the various physical aspects during a Laser Powder Bed Fusion (L-PBF) process. For this purpose, it is necessary to provide a numerical model with specific works on experimental characterizations of materials at high temperature (up to 1000 degrees C) as a model's input parameters, such as the thermal or optical properties of cobalt based powder (CoCrMo) used in our study. In addition to material characterization, theoretical model studies have been used to determine the thermal properties of L-PBF powder [2], in particular thermal diffusivity. This model is also validated by specific experimental characterizations, involving the dilution of iron substrates in a CoCrMo alloy deposit and temperature measurements during the manufacturing process. Furthermore, the amount of iron transferred from the substrate to the coating can be used as an indicator of the molten metal movement in the melt and, ultimately, of the operating parameters used to apply the coating. Too much iron on the surface impairs the mechanical strength of the substrate-coating assembly, thus indicates poor control of the parameters used for this purpose [1].

The Ti-6Al-4V alloy is widely used in aerospace applications for its excellent mechanical properties, however, it presents low wear resistance. It is often coated with a cermet using high-velocity oxy-fuel (HVOF) spraying to improve its wear performance. The Cr3C2-NiCr cermet becomes particularly interesting since it is non-carcinogenic, compared to traditional cermet coatings containing tungsten-cobalt compounds. While the improvement in wear resistance of Ti-6Al-4V with this coating has been demonstrated, its impact on the fatigue performance of the alloy remains to be studied. This is precisely the aim of this study, which focuses on the fatigue life of a Cr3C2-25NiCr-coated Ti-6Al-4V alloy. Among the various influencing factors, surface preparation represents a significant source of crack initiation, particularly in the case of sandblasted surfaces. Indeed, the inclusion of fragmented alumina particles can produce stress concentration zones. Thus, laser texturing, which is a method involving the creation of anchoring points through controlled ablation, can be considered today as a less harmful surface preparation technique. The results obtained from cyclic tensile fatigue tests with a stress ratio of 0.1 for these two surface preparation methods are presented in this paper.

The chemical composition and microstructure of metallic parts are parameters that affect plastic deformation accommodation mechanisms under friction stresses. The content of alloying elements impacts the stacking fault energy and the plastic deformation, and thus affects the tribological behavior. Depending on this content and the levels of mechanical stresses, plastic deformation of some alloys obtained under non-equilibrium conditions can occur. It is caused by different mechanisms, such as perfect slip and/or partial dislocation slip, as well as by phase transformation. The purpose of this study is to determine the influence of the plastic deformation accommodation mechanisms on tribological behavior by studying the effect of the iron content in cobalt-based alloys. For manufacturing purposes, cobalt-based coatings are produced on steel substrate using a additive manufacturing process (SLM). With this process, the microstructures of the cobalt-based coatings are essentially metastable FCC phase at room temperature with different contents of diluted iron. Tribological tests were carried out with a ball-to-disc contact. Iron contents were estimated by EDS-SEM. Analytical techniques such as XRD and EBSD were used to identify the microstructural changes observed in TTS due to tribological loading. The friction coefficient is linked to the evolution of the plastic deformation mechanisms activated to accommodate the contact. In particular, in addition to work-hardening phenomena, phase transformations are possible, namely a metastable FCC phase gives an HCP phase and a metastable FCC phase gives an α′-BCC phase under tribological loading. Both types of transformations can occur, individually or simultaneously, depending on the iron content in the coating.

The Selective Laser Melting process was used to perform cobalt-based alloy coatings on a C35 steel substrate. The relationships between interlayer times, iron dilution, crystalline structures, and micro-hardness were studied for different numbers of layers with an initial lased powder layer of 50 mu m thickness. Reducing the interlayer time increased the temperature reached in the melting bed and promoted matter transport from the substrate. The coating thickness consisted of a Co-Cr-Fe mixture, divided into two zones: a transition zone near the interface and a stabilized zone towards the substrate. The real coating thickness was found to be always greater when the interlayer time was reduced. For an interlayer time equal to 11 s (series 2), the iron dilution was always higher than for an interlayer time ranging between 42 s and 16 s (series 1), leading to a higher coating thickness. The microstructural state was also dependent on the interval time between successive layers. The coating microstructure was always cellular because of the high cooling rate. XRD analysis of the surface showed that this microstructure is essentially composed of two non-equilibrium phases: FCC and alpha' BCC. The high hardness is due to the high content of iron which induces a martensite phase (series 2). Starting from 5 layers for series 1 and from 6 layers for series 2, the alpha' BCC phase disappeared if the iron content on the coating surface was reduced by more than 45% content in weight. The mean coating hardness decreased with an increasing number of layers because of the decrease in the iron content. Finally, the micro-hardness of the FCC phase, for its part, was found to be dependent on the iron content in solution in the Co matrix.

L'efficacite energetique des bâtiments passe par le choix des materiaux utilises dans leur construction tout en tenant compte de l'environnement. Il est bien connu que l'utilisation des briques de terre crue pour la construction de murs permet, d'une part, d'ameliorer le confort thermique des bâtiments et d'autre part, d'apporter un gain dans les couts energetiques en utilisant l'hygrometrie naturelle du logement provenant de l'activite humaine. Le gain sur les couts energetiques est obtenu par la diffusion de la chaleur latente produite suite a la condensation des vapeurs saturees dans le mur. L'objectif de ce projet est d'etudier l'efficacite energetique de ces murs en collaboration avec le Centre de Terre de Lavalette ou des prototypes de murs realises en brique de terre crue sont actuellement en place. Une instrumentation de ces murs avec des capteurs de temperature, d'humidite et de pression a ete realisee a plusieurs positions afin d'observer, quantifier et ameliorer les performances energetiques obtenues par cette diffusion de chaleur latente produite suite a la condensation des vapeurs saturees dans le mur.

In this study, Ti-5Al-5Mo-5V-1Cr-1Fe was implanted with Nb at 45 kV with dosages ranging from 1.0 X 10(16) ions/cm(2) to 1.0 x 10(17) ions/cm(2) in order to investigate their influence on the wear resistance and fatigue performance. The microstructure and elemental depth profiles were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The roughness and mechanical behavior were studied using the optical 3D Infinite Focus and dynamic ultra-microhardness tester respectively. Experimental results indicated that the wear resistance against a GCr15 ball was improved after Nb implantation. Particularly, the specific wear rate of the implanted samples with a dosage of 5.0 x 10(16) ions/cm(2) was lowest (0.2 mm(3).N-1.m(-1)), nearly 10% of the substrate. However, the theoretical fatigue limit of the substrate decreased after Nb implantation. The mechanisms on how wear and high-cycle fatigue properties were affected by Nb implantation with different dosages were discussed in detail.

To evaluate the effects of implantation on fatigue performance of TC18 alloy, Cr and Zr were implanted into specimens using metal vapor vacuum arc plasma source (MEVVA) with a dose of 1 x 10(17) ions/cm(2). The test results show that the fatigue resistance decreased after Cr implantation and Zr implantation, compared to no implanted specimen. The increase in surface roughness after implantation has been found. To analyze the effects of surface roughness produced by ion implantation, the related surface parameters and estimated effective fatigue stress concentration factors was discussed using A&R model. Apart from the residual surface stress and other factors, the surface roughness may have an influence on the fatigue limits of the implanted samples.

The cyclic mechanical behavior, the wear and fatigue resistances and damage developments of working surface of tool steels are dependent on microstructural features. A multi-scale approach combining experimental testing, numerical treatments and simulations is developed to model the surface behavior of X38CrMoV5-1 martensitic tool steels. The multi-scale modeling is coupled with finite element calculations. The elasto-viscoplastic constitutive equations used are based on crystal plasticity model of Méric-Cailletaud and are implemented on the finite element code ABAQUS under a small strain assumption. Trough an appropriate laboratory testing, the microstructure features comparable to the surface of industrial tools or pin/disc in tribology experiments are reproduced by considering plate specimens. Monotonic tensile testing is coupled with in-situ Digital Image Correlation technique (DIC) to determine the surface strain fields. The measured local nonlinear mechanical strain fields are analyzed. The strain localization is related to stereological artifacts. The numerical treatments allow reproducing, qualitatively, the strain localization patterns at the surface observed during tensile testing. The influence of the various stereological parameters such as the morphology of martensitic laths, the crystallographic orientations, the internal hardening state of the surface profiles and their evolutions on the local strain fields are addressed. By such approach, it is possible to get a better insight of some elementary mechanisms acting on tools and/or pin/disc surfaces regarding both tensile and cyclic behavior.

In this paper, a numerical investigation is carried out on the heterogeneous and anisotropic mechanical behaviour of AISI H11 martensitic steel with a multi-scale approach. For this purpose, an elasto-viscoplastic model that considers nonlinear isotropic and kinematic hardenings is implemented in a finite element code using three stress-strain formulations: the small strain assumption where rotation is neglected; and two formulations based on finite strain theory in Eulerian framework which are respectively defined by the Jaumann-Zaremba and the Olroyd objective rates of Kirchhoff stress. The parameters of the constitutive equations are identified using macroscopic quasi-static and cyclic material responses and small strains assumption by the mean of a localization rule. By using particular Voronoi tessellations, a virtual realistic microstructure, consisting of laths and grains, is generated considering the specific crystallographic orientations alpha'/gamma (martensitic/austenitic phases) relation (i.e. Kurdjumov-Sachs relation). Finite element computations are then performed on this virtual microstructure and exhibit that; besides laths orientations, morphologies and interactions; the full-field local mechanical fields are dependant on the used stress-strain formulation.

In this work, a numerical investigation is carried out on the anisotropic and heterogeneous behaviour of the AISI H11 martensitic tool steel surface using finite element method and a multi-scale approach. An elasto-viscoplastic model that considers nonlinear isotropic and kinematic hardenings is implemented in the finite elements code ABAQUS using small strain assumption. The parameters of the constitutive equations are identified using macroscopic quasi-static and cyclic material responses by the mean of a localization rule. Virtual realistic microstructures, consisting of laths and grains, are generated using particular Voronoï tessellations. These microstructures consider the specific crystallographic orientations α’/γ. Finite element investigation is then performed. The local heterogeneous and anisotropic behaviour of the surface as well as the subsurface is shown under quasi-static and cyclic mechanical loadings. The laths morphology and crystallographic orientation have an important impact on the local mechanical fields.

Le projet CANet (CAne NETwork) a ete mis en place en 2011 dans le but de repondre a une problematique societale tout en offrant l'opportunite a differents enseignants et enseignants-chercheurs de competences variees et complementaires de se regrouper autour d'un projet associant un volet recherche pluridisciplinaire a des activites pedagogiques pour nos etudiants d'IUT.

Mechanical bonding and interface behaviour play a key role for any materials deposited on different substrates. Usually, a post-spray heat treatment is required to improve the coating morphology and to enhance mechanical properties of thermal-sprayed polymeric coating. The effects of YAG, CO2 and diode laser radiations on as-sprayed PEEK coating deposited on stainless steel and aluminum substrates were investigated. The results revealed a good coating densification and interface behavior. A correlation between coating and substrate absorption coefficients, their thermophysical properties and laser operating parameters was shown. Besides, the finite element modeling based on IR temperature measurements during diode laser irradiation demonstrated that the densification of organic coating occurs above its melting point.

Flame spraying is frequently used for PEEK coatings elaboration on metallic surfaces. However, this process has a certain number of limitations particularly considering the quality of the coatings like high porosity or low interfacial adherence. For that reason a thermal post-processing is often necessary. From all of the processes which can be used (flame, oven, etc.), laser can be an interesting technology. Then, the aim of this study is to analyse the dependence of the morphological structure (compactness) and the adherence of the flame sprayed PEEK coatings to the stainless steel (304L) and aluminium alloy (AA2017) substrates on laser parameters. Moreover, the influence of the laser beam wavelength (by using a Nd:YAG, CO2 or diode lasers) on compactness of the coating was analysed. Whatever the laser used, it consists to estimate the most optimized parameters to achieve melting without burning the PEEK material.