High-temperature creep behavior of gamma Ti-48Al-2Cr-2Nb alloy additively manufactured by electron beam melting

Abstract

Electron beam melting (EBM) has a lower cooling rate than other additive manufacturing processes (selective laser melting, laser metal deposition, etc.), so it is suitable for manufacturing titanium aluminide-based intermetallics. In this study, a gamma Ti-48Al-2Cr-2Nb alloy was manufactured using EBM, and its microstructure and high-temperature creep behaviors were investigated. Conventional Ti-48Al-2Cr-2Nb was also used for comparison and analysis. Initial microstructural observation confirmed that the EBM-built Ti-48Al-2Cr-2Nb alloy had a near-gamma (NG) structure, whereas the conventional Ti-48Al-2Cr-2Nb alloy had a fully lamellar (FL) structure. Room temperature and high temperature compression tests confirmed that the Ti-48Al-2Cr-2Nb alloy with the NG structure had lower strength in all temperature ranges, and the yield-strength anomaly phenomenon occurred in both materials. A 750 °C multi-step creep test confirmed that the EBM-built Ti-48Al-2Cr-2Nb alloy with lower strength had lower creep resistance as well. Microstructural observation after creep deformation confirmed that dislocation movement and mechanical twins were formed dominantly in the creep deformation of the material with the NG structure. For the material with the FL structure, diffusional creep in low-stress regions and large deformation at the colony boundary in high-stress regions dominated the creep deformation. Correlations between the microstructure, strength, and multi-step creep properties were discussed based on these findings.