Phase equilibria in the Ti-Al-O system at 945 degrees C and analysis of Ti/Al sub 2 O sub 3 reactions

Tie lines were established using equilibrated samples with phase compositions determined by electron probe microanalysis. Phase relations agreed with previous estimates, but the phase fields of alpha -Ti[O,Al] and Ti sub 3 Al[O] differed. The Ti sub 3 Al[O] phase had a max solubility of 22 at.% O, corresponding to a nominal stoichiometry of Ti sub 3 AlO, whereas the alpha -Ti[O,Al] phase, at a max O solubility of 33.33 at.%, had a negligible amount of Al in solution. Disagreement between these results and previous studies was attributed to differences in experimental techniques for sample preparation and analysis. The reported layer sequences at the Ti/Al sub 2 O sub 3 interface were evaluated based on the ternary section and the corresponding O activity diagram. Layered interfaces were stable, with evolution of the reaction products goverened by thickness of the initial Ti layer and pO sub 2 in the ambient.