Compression and compression-compression cyclic deformation properties of ferromagnetic Ni_2MnGa-based shape memory alloy

摘要

Ferromagnetic Ni-25at%Mn-23at%Ga shape memory (SM) alloy was fabricated compositionally uniformly in vacuum using an electric furnace, and its polycrystalline specimens were deformed monotonically in compression and cyclically in compression-unloading -heating-cooling mode at room temperature. Polycrystals deformed in compression at various temperatures showed perfect SM effects and superelastic behavior, and using Clausius-Clapayron relationship, the martensite and its reverse transformation temperatures were determined. Polycrystals failed within several cycles when deformed cyclically at above Mf point, while no failure occurred up to 100 cycles at strain amplitudes between 1.1 and 4.4% when deformed cyclically at near M_s point, although intergranular fracture occurred. The result suggests the Ni_2MnGa alloy should be intrinsically ductile.