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 degrees C and 800 degrees C, three distinct types of gamma phase were observed: gamma lamellae, gamma blocks, and nanoscale gamma clusters. Additionally, nanoscale omega particles were observed to coarsen at 650 degrees C, while they dissolved into the B2 phase after exposure at 800 degrees 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 degrees C. This enhancement was attributed to the dissolution of omega particles and the subsequent precipitation of gamma blocks.