Role of Ti₂Ni precipitates in dynamic recrystallization of near-equiatomic NiTi alloy during hot deformation

This study investigates the dual role of brittle Ti₂Ni precipitates in the dynamic softening of near-equiatomic NiTi alloys by examining their influence on dynamic recrystallization and microstructural evolution during hot deformation. Isothermal hot compression tests were conducted at 700-1000 °C under a strain rate of 0.1 s⁻¹, and the microstructural evolution was characterized by SEM, EBSD, and TEM. The brittle Ti₂Ni phase influences microstructural evolution through two distinct mechanisms, namely particle-stimulated nucleation and Zener pinning, depending on the deformation conditions. When the deformation parameters did not alter the size and distribution of the Ti₂Ni precipitates, coarse Ti₂Ni particles induced local stress concentrations, serving as preferential nucleation sites for discontinuous dynamic recrystallization within the B2 austenite matrix. Conversely, when the deformation parameters promoted mechanical fragmentation and redistribution of Ti₂Ni precipitates, these finely dispersed particles along the flow lines pinned the migration of high-angle grain boundaries, thereby suppressing grain coarsening of recrystallized B2 grains at elevated temperatures and contributing to microstructural refinement.