Abnormal impacts of pre-deformation on the martensitic transformation behaviors of precursory NiTiNb alloys

Abstract

While the effects of pre-deformation on thermodynamically controlled transformation behaviors have been well established in traditional shape memory alloys, it remains unclear whether similar influences apply to kinetically controlled systems. In this letter, we investigate the thermally induced transformation behaviors of pre-deformed precursory NiTiNb alloy specimens, and compare them with those of equiatomic and near-equiatomic binary NiTi of different grain sizes and transformation paths. We show that M_s of NiTiNb increases monotonically with pre-deformation strain, in sharp contrast to the scenario in binary NiTi regardless of the grain size or transformation path. In comparison, A_f of all NiTiNb and NiTi specimens are however insensitive to pre-deformation strain. We suggest that these discrepancies are likely attributed to the enhanced kinetic barrier of nucleation of the forward transformation.