Effect of texture on shape memory property of Ti–16Nb high temperature shape memory alloy

Abstract

Microstructure evolution, texture and shape memory properties of the martensitic Ti−16Nb (at.%) alloy subjected to cold rolling and post deformation annealing were investigated by transmission electron microscopy (TEM), electron backscattered diffraction (EBSD) and Schmid factor analyses. The present alloy deforms mainly by twinning of the {111}o type I or its conjugate, the 211o type II twins along with slip of martensite, when cold-rolled in martensite state. The {112}b111‾b texture of the ex-β grains, in which parallel martensite plates with the {111}o type I or the 211o type II twin relation grow, are formed after post-deformation annealing at 700 °C for 30 min. The orientation effect of {112}b111‾b texture on the Ti−16Nb alloy is analyzed. Both experimental results based on tensile tests and theoretical Schmid factor analysis converge satisfactorily. In result the critical stress for reorientation of martensite variants decreases first, and increases then, as the deviation angle increases. Schmid factor for martensite slip decreases remarkably in the textured Ti−16Nb alloy while the loading direction is parallel to the rolling direction. As a result, slip is introduced difficultly in such case and a total recovery strain of 5% is obtained.