Martensitic transformation and mechanical properties of NiMnGaV high-temperature shape memory alloys

The effect of V substitution on microstructure, martensitic transformation behavior, mechanical and shape memory properties of Ni56Mn25Ga19-xVx (x = 0, 1, 2, 4, 6 at.%) alloys was investigated. Single phase of non-modulated martensite with tetragonal structure is observed for x = 0 and x = 1, and dual phases with tetragonal martensite and face-centered cubic γ phase are present for x ≥ 2. The volume fraction of the γ phase increase with the increase of V content up to 41 vol%. The martensitic transformation temperatures decrease with V content increasing from 1 to 6 at.%, which is mainly attributed to the reduction of electron concentration of martensite. The compressive fracture strength and strain increase from 346 MPa and 10.0% for x = 0 to 1429 MPa and 31.0% for x = 6. Therefore, γ phase can markedly enhance the mechanical properties. As γ phase particles on martensite are barriers to its shape recovery, the shape memory strains decrease a little with increasing V content when x ≤ 2, and then drop remarkably from x = 2 to x = 6.