Microstructure evolution and oxidation behaviour of Tif/TiAl3 composites

In this paper, Tif/TiAl3 composites were fabricated by infiltration-in situ reaction method and its oxidation behaviours were investigated by cyclic oxidation testing at 700 oC, 800 oC and 900 oC. The microstructure evolution and oxidation of Tif/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 oC, and four reaction layers surrounding Ti fibre (Ti3Al, TiAl, TiAl2 and TiAl3 from inner to outside) were observed above 800 oC. 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 Tif/TiAl3 composites decreased with increasing of temperature, and changed from cubic law at 700 oC to parabolic law at 900 oC. The oxidation weight gain of Tif/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 oC changed to mushroom-shape. Fortunately, when TiAl3 was oxidized, a thin and continuous Al2O3 layer was formed, protecting matrix from further oxidation.