High pressure studies on a prototype omega forming alloy system

Abstract

High pressure studies have been carried out on a prototype omega forming alloy system, i.e. Titanium-Vanadium. In particular, omega phase formation was investigated under combined thermal and pressure treatment. High pressure resistivity measurements were followed by X-ray diffraction and transmission electron-microscopy of the pressure treated samples to see the pressure induced structural changes. These studies on quenched Ti---5 at.% V and Ti---10 at.% V alloys indicated, (a) lowering of ω- start pressure with the addition of vanadium and (b) presence of an intermediate b.c.c. (β) phase during the course of pressure induced h.c.p. (α) to simple hexagonal (ω) transformation. The morphology and crystallography of the α⇋ω transformation is investigated in detail. Application of pressure on quenched single phase b.c.c. (β) alloys showed that similar to thermal treatment, β→ω transformation occurs under pressure also and that the transformation pressure increases rapidly with increase in vanadium concentration. The results obtained from various representative compositions of alloys are in general agreement with the free energy curves for A---B alloy system suggested earlier using band theory description of metallic cohesion. Based on our studies, equilibrium and metastable P-X (Pressure-Concentration) diagrams for A---B omega forming alloy system have also been suggested.