Relationship between texture and macroscopic transformation strain in severely cold-rolled Ti-Nb-Al superelastic alloy

Textures of severely cold-rolled Ti-24 mol%Nb-3 mol%Al superelastic alloy were examined by X-ray pole figure measurements for the bcc parent phase (beta) and the relationship between transformation strain and loading direction was evaluated on the basis of the lattice correspondence and change in the potential energy of an external stress. A well-developed recrystallization texture of <110>(beta){112}(beta) type was confirmed by X-ray pole figure measurements for the material which was 99% cold-rolled followed by a solution-treatment at 1273 K. Crystallographic analysis showed that the maximum dilatation component of the martensitic transformation from beta to alpha" is <110>(beta) parallel to the rolling direction (RD). An energy consideration revealed that only one alpha"-variant (lattice-correspondence variant) can be induced by the tensile stress along RD when the recrystallization texture appears. The transformation strain generated under the RD tension was about three times larger than that generated under the tension along transverse direction (TD). These calculations were in good agreement with experimental evidences.