Improvement in the high-temperature creep properties via heat treatment of Ti-6Al-4V alloy manufactured by selective laser melting

This study seeks to control the microstructure of Ti-6Al-4V alloy produced by a selective laser melting process using only heat treatment, while also improving the high temperature creep behavior. Initial microstructure observation showed a fully martensite structure for the as-fabricated specimen and a fine widmanstätten structure for the heat-treated specimen. Hardness tests indicated that the hardness of the material decreased somewhat, but the anisotropy of the mechanical properties (common in additive manufactured materials) disappeared. Compression tests at 500 °C indicated that the yield strength of the as-fabricated specimen was approximately 930 MPa, while in the heat-treated specimen it was approximately 557 MPa. High temperature compressive creep tests showed that the heat-treated specimen had relatively low creep strain and low steady-state creep rate (superior creep resistance) in all stress ranges, which is the opposite of the compressive yield strength results. After creep deformation, the microstructural evolution of the as-fabricated and heat-treated specimens was compared, and the microstructure changed much more extensively in the as-fabricated specimen. Correlations between microstructures, hardness, strength and creep properties were discussed based on these results.