Build orientation, part size geometry, and scan path influence on the microstructure and fatigue life of Ti-6Al-4V fabricated by Electron Beam Melting

Electron beam melting (EBM), a powder bed fusion process, is a rapidly-developing metal additive manufacturing method that allows for fabrication of complex geometries directly from a computer file that would be difficult or impossible to fabricate by traditional methods. EBM holds significant interest in the aerospace industry for the high-strength titanium alloy, Ti-6Al-4V, because of its promising opportunity to reduce buy-to-fly ratios. However, a fundamental understanding of the fatigue-damage tolerance, underlying mechanisms, and impact of processing conditions is required for use of EBM fabrication of critical flight components. To investigate how the EBM process affects components, different parameters were varied and the resulting microstructure and mechanical properties were characterized using 4-point bend fatigue tests, tensile tests, Vickers microhardness indentations, scanning electron microscopy, and optical microscopy.The orientation, scan path, and surface finish were varied and the effects on microstructure, tensile properties, and fatigue behavior are reported and discussed. As expected, the surface roughness left by the EBM fabrication adversely impacts the fatigue behavior and sufficient machining is required to remove all surface roughness effects. It was discovered that the build orientation affects the tensile ductility and fatigue life, but the strength and hardness are largely independent of orientation. The EBM Ti-6Al-4V shows similar fatigue life to conventional material, but is limited by porosity defects. The altered processing parameters affected the fatigue behavior, but promising results indicate that EBM can be a viable manufacturing method for flight critical components.