Fatigue properties of a titanium alloy (Ti-6Al-4V) fabricated via electron beam melting (EBM): Effects of internal defects and residual stress

A clear understanding of the fatigue properties of Ti-6Al-4V manufactured with electron beam melting (EBM) is needed to ensure performance in critical applications in the medical device and aerospace industries. In this work, the effects of residual stress and internal defects (pores and voids) on fatigue properties of EBM Ti-6Al-4V material in as-built, stress-relieved, and hot isostatic pressed (HIPed) conditions were evaluated. Conventional techniques were used to measure the chemical composition and quantify microstructures, and neutron scattering was utilized to measure residual stresses. Post-processing did not alter chemical composition. Compared to the as-built condition, microstructure was unchanged for stress-relieved material and coarser for HIPed material. No significant residual stresses were measured for any of the three conditions. This indicates build platform and layer preheating lead to sufficient process temperatures to achieve full stress relief in-situ. The fatigue strengths at 107 cycles measured for the as-built and stress-relieved conditions were statistically similar and were measured to be 200-250 MPa. A significantly higher fatigue strength at 107 cycles of 550-600 MPa was measured for the HIPed condition. The increase in fatigue endurance limit was attributed to a reduction in internal porosity and void content.