Thermo-Mechanically Assisted Grain Growth in Ti6Al4V Fabricated Using the Powder Bed Additive Manufacturing During High-Temperature Mechanical Testing

High-temperature mechanical behaviors of metal alloys and the underlying microstructural variations responsible for such behaviors are important areas of interest for many industries particularly in their high-temperature applications. Transformation of grains which occur both during metal powder bed fusion additive manufacturing processes due to variation of thermal gradient and cooling rates, and afterward during different thermomechanical loads that parts experience in their specific applications, could also impact its mechanical properties both at room and high temperatures. This study focuses on in-depth analysis and understanding of how the grain structures of electron beam powder bed fusion (EB-PBF) Ti6Al4V alloy changes during high-temperature mechanical load, due to the interacting mechanisms. Mechanical testing is conducted for EB-PBF parts made at different build orientations up to 600 °C. Microstructural analysis using electron backscattered diffraction (EBSD) is conducted on samples before and after high-temperature mechanical testing to understand the interacting impact that temperature and mechanical load have on the activation of deformation mechanisms. EBSD analysis showed both grain size and grain orientation to be dependent on the build orientation. Mechanical testing at high temperature showed softening behavior especially from 400 °C to 600 °C temperature. Additionally, anisotropic behavior was observed which is associated with volume ratio of β phase as well as the anisotropic grain formation. Some grain coarsening was observed at higher test temperatures. Additional changes in misorientation angle and certain preferred grain orientation that varies with temperature signifies activation of geometric deformation mechanism.