Uncovering the role of nanoscale precipitates on martensitic transformation and superelasticity

We characterize the role of coherent nanoscale B2 Ni50Al50 precipitates on temperature- and stress-induced martensitic phase transformation in nanocrystalline Ni63Al37 shape memory alloys using multi-million-atoms molecular dynamics (MD) simulations. studied two types precipitates: one with single crystal (SXP) a second where grain boundaries cut through (PXP). Simulations reveal that presence stabilizes cyclic flag-shaped stress-strain response, characteristic superelasticity, reduces remnant strain. In contrast, single-phase exhibits degradation reverse during loading and, eventually, incomplete reversible within few cycles. This is consistent previous experimental findings ultra-low fatigue Ni-Ti-Cu Ti2Cu precipitates. The simulations significantly improves reversibility by acting as elastic zones partially shield drive transformation. A detailed analysis MD trajectories reveals matrix induces ultra-large deformation some (approximately 12%) to point resulting martensite-like atomic structure.