Fatigue performances of selective laser melted Ti-6Al-4V alloy: Influence of surface finishing, hot isostatic pressing and heat treatments

In this study, a detailed evaluation on the effects of different surface finishing processes, hot isostatic pressing (HIP) and heat treatments on the fatigue performance of SLMed Ti-6Al-4V is conducted. It is found that surface finishing processes of turning, grinding, grinding followed by sandblasting and polishing can effectively reduce the surface roughness of as-SLMed surfaces (R-z = 68.66 mu m) and significantly improve the fatigue performances. The HIP, HT-920 and HT-850-550 treatments can significantly improve the ductilities of SLMed Ti-6Al-4V due to the coarsening of a laths and formation of 13 grains. The ultimate tensile strengths (UTSs) and yield strengths (YSs) of HIPed and HT-920 specimens reduce more than 140 MPa, while those of the HT-850.550 specimens show no obvious reduction. The SLMed Ti-6Al-4V specimen has a fatigue limit lower than 300 MPa, while the HT-920 and HT-850-550 treatments enhance the threshold of crack growth and increase the fatigue limit to 350-400 MPa. The reduction or elimination of pores and the modification of microstructure in HIPed specimens both significantly extend the period of fatigue crack initiation, leading to an increased fatigue limit of 450-500 MPa.