Microstructural Development of Ti-Al Thin Films During Annealing

Abstract

Titanium aluminides, based on TiAl and Ti₃Al, are potential materials for high temperature aerospace application. Their low density, high temperature creep resistance and strength, high oxidation resistance, make them excellent potential engine materials. It is reasonable to develop processing strategies for protective and high temperature coating based on them. On magnetron sputtering, the Ti- 48% Al alloy thin films, the composition of which corresponds to the target’s one, have been obtained. When annealed, the aluminium atoms have been discovered to diffuse into the substrate and the redistribution, as well as the leveling of the films’ compositions in the volume, take place. After annealing, the film contains a higher titanium concentration. On sputtering, the formation of the Ti₃Al-based metastable phase in the films has been observed. This phase is the main in the films and has a different morphology on different substrates. It is stable and doesn’t decompose at annealing. During annealing, the new intermediate metastable phases, which are stable within a finite temperature and concentration range, have developed. The structure, kinetics of phase transformation and evolution of the film microstructures, depend on the structure and morphology of the substrate.