The effect of a novel low-temperature vacuum heat treatment on the microstructure and properties of Ti–6Al–4V alloys manufactured by selective laser melting

Abstract Low-temperature vacuum heat treatment can mitigate the possibility of thermal deformation in metals, especially printed parts with complex structures. In this work, a novel low-temperature vacuum heat treatment processing of a Ti–6Al–4V alloy manufactured by selective laser melting was investigated. The results show that many low-angle grain boundaries and dislocations exist in the Ti–6Al–4V alloy fabricated by selecting laser melting; therefore, the as-built Ti–6Al–4V alloy has high strength. The comprehensive performance of the Ti–6Al–4V alloy is better when the heat treatment temperature is 550 °C/4 h and the ultimate tensile strength, yield strength and elongation are 1220 MPa, 917 MPa and 11.6%, respectively. Compared with the as-built parts, the heat-treated Ti–6Al–4V alloy (via low-temperature heat treatment) exhibits a slightly improved strength and a 26% increase in elongation, resulting in a combination of high strength and good ductility. Additionally, the tensile properties are equivalent to those after high temperature annealing at 800 °C. With this heat treatment process, more β phases are precipitated, which serve as the second strengthening phase. Furthermore, a large number of twins can enhance the plasticity. However, as the temperature continues to rise, the β precipitated phase becomes coarser, and the corresponding strength decreases.