Martensitic behaviour in the equi-atomic Ni-Ti alloy

Abstract

The martensite transformation which occurs either thermally or by plastic deformation in the equi-atomic Ni-Ti alloy has been studied in detail by transmission electron microscopy. The transformation occurs by alternate simple shears on {112} planes and in ⟨111⟩ directions of the parent B2 structure. These shears convert the original lattice into two distinct close-packed monoclinic martensites which may be described as distorted hexagonal close-packed structures if atom types are not considered. In this manner the deformation associated with the transformation is almost perfectly compensated without the introduction of any additional defect. The movement of the atoms involved in this transformation has been determined, in turn accounting for the remarkable memory effect associated with this material.