Microstructure and mechanical properties of Ti–6Al–4V fabricated by electron beam powder bed fusion regulated via hot isostatic pressing

Abstract

Electron Beam Powder Bed Fusion Additive Manufacturing (EB-PBF AM) has gained significant industrial recognition due to its advantages in geometric design flexibility, functional integration, and integrated forming. However, EB-PBF fabricated parts are subject to internal gas pores and lack-of-fusion defects accompanied by the formation of metastable α′ martensite in microstructure. To address these challenges, this study employs hot isostatic pressing (HIP) post-processing for microstructure modification and defect elimination, systematically investigating the influence of HIP temperature (880 °C, 920 °C, 960 °C) on microstructure evolution and tensile properties of Ti–6Al–4V alloy. Experimental results demonstrate that the α phase undergoes significant coarsening with increasing HIP temperature, accompanied by the formation of spheroidized α phase particles. Variant selection analysis reveals a monotonic decrease in variant selection intensity with ascending HIP temperatures. After HIP treatment at 920 °C, the samples achieve optimal strength-ductility balance (ultimate tensile strength: 852 MPa, elongation: 18.2 %), primarily attributed to their moderate α phase dimensions and β phase content. Interestingly, despite α phase coarsening after 960 °C HIP compared to 920 °C HIP, the strength exhibits a paradoxical increase, which is attributed to a higher proportion of hard oriented α and the coarsening interface phase for the strengthening of interfacial barriers.