25 Mai – Thesis defense - Sarah Milhomme

10 h30 Amphi 31 - ESTIA (Bidart)

Influence of process on mechanical and microstructural properties of Ti-6Al-4V additively manufactured parts (LMD and SLM).

The relations between metal additive manufacturing parameters and obtained parts properties, in terms of microstructures, defects and mechanical behavior, are not yet fully understood. In addition, performing post-processing treatments on AM parts is common to improve their properties. The aim of this study is to connect these properties. The first part of this work focuses on producing bulk parts with
two metallic additive manufacturing processes: LMD and SLM. A parametric study for the LMD process and the research of suitable supports for the SLM process were necessary. The parts were characterized in terms of microstructure, defects and residual stresses. The obtained microstructure is similar for both processes, although primary grains are bigger for LMD parts. Internal and surface defects analysis showed a heterogeneous material integrity in LMD parts. Residual stress measurements highlighted the presence of compressive stresses related to the machining of the surfaces. The tensile properties of the TA6V alloy depend on the manufacturing process. However, after hot isostatic pressing, the fatigue properties are identical regardless of the process used. Effects of post-processing, loading direction and surface condition were investigated in LMD. The surface roughness has a critical effect on the fatigue resistance. Numerical calculations have been performed on real surfaces of LMD parts. A numerical procedure from literature
was adapted to calculate a fatigue indicator parameter and to predict fatigue resistance reduction for rough parts, compared to a surface without defects. Numerical results are slightly below experimental results but validate an effective methodology to optimize the manufacturing parameters for rough parts.

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