Formation process of Ti3Al in Ti/Al2O3 system

It has been reported that Ti reduces Al2O3 forming Ti3Al at the interface. From the viewpoint that the structural change of the Ti3Al phase influences the metal-ceramic joining strength, the Ti3Al formation process was analyzed by XPS, XRD, TEM and RBS. Titanium films were deposited on the ((1) over bar 10 (2) over bar) surface of Al2O3 substrates and annealed. XRD analysis shows that Ti3Al formation starts at 1073 K. Initially, the (11 (2) over bar 0) and (20 (2) over bar 0) Ti3Al planes are oriented parallel to the surface. After 1173 K-300 s heat treatment, XRD shows only the (20 (2) over bar 0) Ti3Al peak; After 1173 K-600 s heat treatment, HREM observation shows that the lattices of the Ti3Al (0 (2) over bar 20) plane match those of the Al2O3 ((1) over bar 2 (1) over bar 0) plane at the interface. It is suggested that the (20 (2) over bar 0) oriented grains grow preferentially on the ((1) over bar 10 (1) over bar) Al2O3 plane. The quantity of formed Al increases with heating time. After 420 s, the rate of Al formation falls off. The rate of the Al2O3 reduction is in good agreement with the slightly modified Johnson-Mehl equation. The Ti2O/Ti3Al(O)/Al2O3 layer sequence and morphology can be explained by the pure Ti decrease.