Ternary intermetallic phases in Ti-A1-Nb system and microstructure of the Ti-30Al-20Nb (at%) alloy based on their coexistence

The paper discusses the structure and formation of two ternary ordered phases of Ti-Al-Nb system - close-packed Ti2AlNb and omega-type B82 Ti4Al3Nb. The two phases appear to be in thermodynamic equilibrium with each other at temperatures up to 900 degrees C. Both phases can be considered as products of different displacive transformations from the cubic high-temperature B2 phase. The paper also discusses a new heterophase Ti-30Al-20Nb alloy microstructure which is based on the coherent mixture of the two ternary phases. High strength of the alloy is achieved when these alloys are induced by proper heat treatment to form a natural composite of these two intermetallics: the orthorhombic Ti2AlNb O phase known to have some ductility and the plasticly unsheareble omega-type B82 phase. High specific strength and microstructural stability at elevated temperatures make these alloys a possible candidate for aerospace applications