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

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 {1 1 1}(o) type I or its conjugate, the 2 1 1(o) type II twins along with slip of martensite, when cold-rolled in martensite state. The {1 1 2}(b) 1 1 (1) over bar (b) texture of the ex-beta grains, in which parallel martensite plates with the {1 1 1}(o) type I or the 2 1 1(o) type II twin relation grow, are formed after post-deformation annealing at 700 degrees C for 30 min. The orientation effect of {1 1 2}(b) 1 1 (1) over bar (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.

Automated summary

The microstructure evolution, texture, and shape memory properties of the martensitic Ti-16Nb alloy after cold rolling and post deformation annealing were investigated. The alloy deforms mainly by twinning and slip when cold rolled in martensite state, and forms a specific texture after annealing at 700℃. The orientation effect and Schmid factor analysis on the alloy were analyzed, showing a decrease in critical stress for reorientation of martensite variants and a decrease in Schmid factor for martensite slip in the textured alloy.