Structure, Martensitic Transformations, and Mechanical Properties of Aging Nanocrystalline Ti–50.9 at % Ni Alloy

The effect of aging temperature in the range of 300–500°C on the structure, R martensitic transformations and mechanical characteristics of nanocrystalline Ti–50.9 at % Ni alloy with a grain/subgrain structure was studied. It was found that variation in the spatial distribution of coherent Ti₃Ni₄ particles in the nanostructure from location on dislocations during low-temperature aging to precipitation at dislocation boundaries under accelerated aging is accompanied by a change in the morphology of the R phase from a nanodomain to a self-accommodating lamellar structure. The nanodomain structure of the R phase contributes to homogeneous deformation of the alloy during loading/unloading and stabilization of superelasticity. When loading the alloy with a lamellar R-phase morphology, localized deformation bands are formed by the R-phase reorientation in a Lüders deformation manner.