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

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 degrees 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 degrees C. With this heat treatment process, more beta 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 beta precipitated phase becomes coarser, and the corresponding strength decreases.

Automated summary

Low-temperature vacuum heat treatment can reduce thermal deformation in metals, and the Ti-6Al-4V alloy manufactured by selective laser melting shows high strength and good ductility after heat treatment at 550 degrees C for 4 hours. The precipitation of more beta phases and the presence of twins enhance the plasticity of the alloy, but higher temperatures can lead to coarser precipitated phases and decreased strength.