Proton irradiation induced phase transformation in Ni-Mn-Ga thin films

[Display omitted] •The defects type induced by irradiation remains same and density elevates with dose.•The point defects generates compressive stress of 4 GPa in the film.•The sress by proton irradiation induces 7 M martensite formed in austenitic films. This paper reports the martensitic transformation of NiMnGa film induced by proton irradiation, which is of great significance for evaluating the reliability of NiMnGa film. Ni-Mn-Ga thin films are spotlighted as next-generation alternatives to currently used micro-actuators in the MEMS system for aircraft. Nonetheless, their potential applications are hindered by the stability under proton irradiation in the space. In the present manuscript, the microstructure evolutions of Ni50Mn25Ga25 thin films are investigated under various proton irradiation doses. A large number of point defects are introduced into the thin films at the irradiation dose over 1 × 1016 p/cm2 as indicated by the positron annihilation spectrum. And the type of defects remains the same after irradiation Consequently, 7 M martensite is formed on the surface of austenitic Ni50Mn25Ga25 thin films driven by the internal stress filed based on the GI-XRD and TEM observations.