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Analyse des microstructures et étude du comportement mécanique de pièces en alliage de Ti-6Al-4V issues d'un procédé de fabrication de poudre métallique

Abstract : This study is concerning the additive manufacturing process of powder bed fusion named DIRECT METAL LASER SINTERING (DMLS) which is similar to the SELECTIVE LASER MELTING process. An important amount of academic documentation exists on those processes especially focused on building parameters and their impacts on mechanical properties of built parts. In the industrial application, the accessibility of all printing parameters is generally not possible. Indeed, building parameters are incorporated by machine makers within the printers, and characteristics of built parts are guaranteed by the printing process. For industrial, scientist publications do not take all DMLS process in integrity but only specific parts which cannot lead to optimal control of built parts. The general problem of this study is to focus on the DMLS process with titanium Ti-6Al-4V alloy material. Building parameters investigated in this study are those our industrial partner can influence which include printing machine, reused powder, layer thickness, built orientation, polishing and heat treatment. The main data analysis on built parts are porosity, surface roughness, microstructure (phases analysis), and mechanical properties on tensile, fatigue, and hardness tests. A design of experiments was realized to establish relationships between some builds parameters and results from the data analysis. Powder analysis is showing a sphericity deterioration with a high level of reused powder which can increase Vickers hardness. However, no link can be established with morphological deterioration, therefore the increase in hardness is due to chemical composition variation. Layer thickness does not influence mechanical properties even though high layer thickness leads to an increase of volume and porosity. The orientation effect on the sample is mainly shown at 0° orientation during the fatigue test. At this orientation, the number of cycles of life of the sample is increased even though the 0° orientation is the angle with the maximum number and volume porosities. The hot isostatic pressing treatment is one with the most influence. His realization highlight the phase transformation of martensitic a” to dual phase α + β phase. This heat treatment also reduces the number and volume of porosities. From a macroscopic perspective, this heat treatment leads to an increase of elastic modulus and elongation break but reduces yield stress and ultimate tensile strength. Finally, the decrease of Vickers hardness is shown with the modification of microstructure. The polishing effect is also another main parameter which leads to a decrease in surface roughness and an increase of mechanical properties during the fatigue test due to the limitation of surface cracks. To finish, the interaction between HIP treatment and polishing has a major influence on mechanical properties when combined. This is observed from tensile and fatigue tests as an important increase in mechanical properties. To conclude this study, statistics laws between built parameters and mechanical properties have been established. An evaluation of these laws was completed with an ultimate fabrication made by the industrial partner.
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https://tel.archives-ouvertes.fr/tel-03198724
Contributor : Mathias Cesbron Connect in order to contact the contributor
Submitted on : Tuesday, January 18, 2022 - 4:03:48 PM
Last modification on : Tuesday, January 25, 2022 - 3:06:51 AM

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  • HAL Id : tel-03198724, version 2

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Mathias Cesbron. Analyse des microstructures et étude du comportement mécanique de pièces en alliage de Ti-6Al-4V issues d'un procédé de fabrication de poudre métallique. Génie mécanique [physics.class-ph]. Université Savoie Mont-Blanc, 2020. Français. ⟨tel-03198724v2⟩

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