Size effects of NiTi nanoparticle on thermally induced martensitic phase transformation

Abstract Molecular dynamics simulations are performed to study the thermally induced martensitic phase transformation (B2-B19′) of NiTi free-standing nanoparticles. We successfully reproduce the experimental observations that the martensitic transformation temperature decreases with reducing particle size and the martensite may form self-accommodated herringbone morphology. It is found that a core-shell structure with shell thickness of 0.3 nm (approximately equal to one unit cell) exists in NiTi nanoparticles and the B2-B19′ transformation is dominated by the core region. In addition, three detwinning manners are observed in the reverse martensitic phase transformation (B19′-B2) process. It is concluded that the suppression of B2-B19′ transformation in NiTi nanoparticles is due to the lack of nucleation sites and the size dependent martensitic morphology originates from the constraints of surface shell.