Improved fatigue endurance ratio of additive manufactured Ti-6Al-4V lattice by hot isostatic pressing

Abstract Selective laser melting (SLM) is a dominant additive manufacturing (AM) method of fabricating various porous and high-density metallic materials with complex geometries. However, the SLM porous materials generally exhibit inferior fatigue performances, particularly the endurance ratio. The main purpose of this study was thus to investigate the influence of hot isostatic pressing (HIP) on the fatigue property of SLM Ti-6Al-4V lattice with a self-designed unit cell. The results show that HIP treatment at 1000 °C/150 MPa can eliminate the pore in the strut and respectively decreases the microhardness from 403 HV to 324 HV and the yield strength from 143 MPa to 100 MPa. Furthermore, the fatigue strength and the endurance ratio at 10 6  cycles are increased after HIP. The HIP process sufficiently improves the fatigue endurance ratio at 10 6  cycles of SLM lattice from 0.3 to 0.55, which is comparable to that of the solid metallic material. This improvement can be predominantly attributed to the phase transformation from brittle α′-martensite to tough α + β mixed phases after HIP. The tougher α + β mixture can help resist the propagation of fatigue cracks by crack blunting and thus improve the fatigue properties.