Microstructure and fatigue performance of SLM-fabricated Ti6Al4V alloy after different stress-relief heat treatments

The main interest in Additive Manufacturing (AM) technology relates to its ability to produce complex components with relatively reduced weight that are difficult to produce or cannot be produced by other conventional technologies. Selective laser melting (SLM) is extensively used, as one of the AM technologies to fabricate metallic parts. This advanced method allows to produce various parts with complex geometries with high three-dimensional (3D) accuracy from fusion powders in a layer-by-layer style. Ti6Al4V alloy is a widely used material for structural applications in aerospace and biomedical due to high specific fatigue strength. SLM processing makes this alloy attractive when weight reduction is a design objective. The SLM Ti6Al4V microstructure is influenced by process parameters and build orientation. The localized high energy input during very short interaction times leads to the formation of very fine structures and to the generation of internal stresses. Therefore, the SLM parts are heat treated to decrease or completely remove residual stresses. The present study aims at evaluating the effect of stress-relief heat treatments on the microstructure, the mechanical properties and the fatigue performance of SLM Ti6Al4V alloy. Ti6Al4V alloy specimens were manufactured according to the SLM process with an EOS M290 system. Post fabrications heat treatments at different temperatures (i.e. 740˚C vs. 900˚C) resulted in different structure and mechanical properties that were identified and measured. Fatigue testing of specimens with as-built surfaces was performed at room temperature on modified Schenk-type fatigue testing machine applying a pulsating plane bending (load cycle ratio R = 0) to the specimens at a frequency f = 15 Hz.