Microstructure evolution and oxidation behaviour of Ti_f/TiAl₃ composites

In this paper, Ti_f/TiAl₃ composites were fabricated by infiltration-in situ reaction method and its oxidation behaviours were investigated by cyclic oxidation testing at 700°C, 800°C and 900°C. The microstructure evolution and oxidation of Ti_f/TiAl₃ composites were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray diffraction (EDX). The reaction between Ti₃Al particles and Al was more violent than that of Ti fibres and Al. Ti₃Al/Al reaction consumed a large amount of Al and inhibited the reaction of Ti fibres indirectly. Reactant of Ti fibres was TiAl₃ at 700°C, and four reaction layers surrounding Ti fibre (Ti₃Al, TiAl, TiAl₂ and TiAl₃ from inner to outside) were observed above 800°C. The thickness of the total reaction layers increased little with temperature and time, while the thickness of inner reaction layers increased remarkably. A model corresponding to the microstructure evolution process was drawn schematically. Oxidation resistance of Ti_f/TiAl₃ composites decreased with increasing of temperature, and changed from cubic law at 700°C to parabolic law at 900°C. The oxidation weight gain of Ti_f/TiAl₃ composite was dominated by the exposed Ti fibres. Due to outward diffusion of Ti and Al element, the oxide of Ti fibre at 900°C changed to mushroom-shape. Fortunately, when TiAl₃ was oxidized, a thin and continuous Al₂O₃ layer was formed, protecting matrix from further oxidation.