Mechanism of microstructure evolution and mechanical properties of high Nb-TiAl alloy in transition zone of laser-deposited Ti60/TiAl alloys

The transition zone of the Ti/TiAl alloy with a nominal composition of TiAl-5.5Nb was fabricated using laser melting deposition (LMD) of a powder mixture consisting of 30 % Ti60 and 70 % Ti-45Al-8Nb (wt. %). The microstructural evolution and mechanical properties were investigated. Upon thermal exposure at 650 °C and 800 °C, three distinct types of γ phase were observed: γ lamellae, γ blocks, and nanoscale γ clusters. Additionally, nanoscale ω particles were observed to coarsen at 650 °C, while they dissolved into the B2 phase after exposure at 800 °C. Notably, the tensile strength, yield strength, and plastic elongation of the specimens were significantly improved by 25.5 %, 23.9 %, and 47.2 %, respectively, following thermal exposure at 800 °C. This enhancement was attributed to the dissolution of ω particles and the subsequent precipitation of γ blocks.