PHASE-EQUILIBRIA IN THE TI-AL-O SYSTEM AT 945-DEGREES-C AND ANALYSIS OF TI/AL2O3 REACTIONS

Phase relations in the Ti-Al-O system were evaluated experimentally at 945 degrees C. The tie lines were established using equilibrated samples with phase compositions determined by electron probe microanalysis, The phase relations were in agreement with previous estimates but the phase fields of alpha-Ti[O,Al] and Ti3Al[O] were significantly different, The Ti3Al[O] phase has a maximum solubility of 22 at,% O, corresponding to a nominal stoichiometry of Ti3AlO, whereas the alpha-Ti[O,Al] phase, at a maximum O solubility of 33.33 at.%, has a negligible amount of Al in solution. The disagreement between these results and previous studies was attributed to the differences in experimental techniques for sample preparation and analysis, The reported layer sequences at the Ti/Al2O3 interface were evaluated based on the ternary section and the corresponding O activity diagram, The layered interfaces were found to be stable, with the evolution of the reaction products governed by the thickness of the initial Ti layer and the O partial pressure in the ambient.