Formation and reversion of stress induced martensite in Ti-10V-2Fe-3Al

Abstract

The formation and reversion behavior of stress induced orthorhombic martensite (α″) in Ti-10V-2Fe-3Al has been studied, and several interesting features found. Reversion appears to take place in four stages. First, there is an athermal reshearing of α″ back to the b.c.c. parent phase, which is accompanied by a significant one-way shape memory effect between 165° and 240°C. This athermal reversion competes with an isothermal stabilization of the α″ plates. Further heating results in the isothermal precipitation of α, which seems to reproduce the preferred orientations of the previous α″, and is thus also accompanied by a shape memory effect; an isothermal shape memory effect in the opposite direction as the preceeding athermal shape change. The precipitation of α occurs on two microstructural scales, extremely fine α nucleating in the β matrix on extant isothermal ω particles, and the direct transformation of the unreverted α″ plates to α. Finally, when heating is continued to the β-transus temperature, the α begins to dissolve back to the parent β. This final dissolution is accompanied by a textural loss in the α phase, and consequently gives rise to several final “shape adjustments”, the nature of which have not been fully explained.