Microstructure and martensitic transformation of an ultrafine-grained TiNiNb shape memory alloy processed by equal channel angular pressing

•Microstructure of the as-ECAP processed TiNiNb alloy is inhomogeneous.•Transformation temperatures are lower than those of the initial material.•Transformation stability and mechanical properties can be considerably improved.

Microstructure, martensitic transformation and mechanical properties of an ultrafine-grained Ti44Ni47Nb9 shape memory alloy processed by equal channel angular pressing were investigated. The as-ECAP processed sample is characterized by an inhomogeneous and refined microstructure. In β-Nb phase-rich region, the grains of matrix are elongated with high density dislocations. In β-Nb phase-free region, the microstructure is partial recovery and characterized by near-equiaxed grains. The heterogeneous microstructure is attributed to presence of β-Nb phase. Martensitic transformation behavior of the as-ECAP processed sample is characterized by a single-stage transformation. The thermal cycling stability of transformation and the mechanical properties are considerably improved due to a strengthening effect resulting from refined grain size and high dislocation density.