A reconsideration of phase relations in the Ti-Al-Mo and Ti-Al systems

A microstructural and X-ray investigation of Ti-AI-Mo alloys Ti-31 Al-15 Mo, Ti-31 Al-13 Mo, Ti-31Al-9Mo and Ti-35Al-9Mo (containing the Ti3Al, TiAl and β phases) indicates that the existing phase diagram of the ternary system for this composition range published by Ge Dhzhi-Min and Pylaeva is in error above 1473 K. An analysis of phase relations reveals that the error has arisen from their use of the Ti-AI diagram due to Bumps, Kessler and Hansen as a basis for generating the ternary. It is shown that a phase diagram of the ternary, consistent with the experimental results, can be generated using a version of the Ti-AI system due to Margolin. Simple geometric arguments are used to build up a new semi-quantitative description of the Ti-AI-Mo system which can be used as a basis for a detailed investigation of phase equilibria in this system.