Study of Phase Equilibria and Transformations in the Nb-Ti-Al System

摘要

In this project, research effort was directed into phase equilibria and transformations in the Nb-Ti-Al system and in multicomponent gamma titanium aluminides. The sequence of transformations site occupancies and stable phases in a 37Nb-37Ti-26Nb alloy were established, together with tie-lines at a number of temperatures between 1000 - 1300 deg C. The effect of beta-phase stabilizers, boron additions and thermal history on transformation pathways. modes, kinetics and microstructure in gamma Ti-Al alloys were established. Furthermore, isothermal and continuous cooling transformations for gamma alloys across a range of compositions from binary and ternary bases to multicomponent chemistries were studied. The reactions sequences for alpha and beta phases were quantified and partial CCT diagrams established for two multicomponent alloys. Mechanisms associated with various transformation modes are discussed.