Phase equilibria and composition dependence of martensitic transformation in Ni–Mn–Ga ternary system

Phase equilibria of Ni–Mn–Ga ternary system at 800 °C, 900 °C and 1000 °C were experimentally investigated by the diffusion couples and equilibrated alloys. The results show that the bcc phase possesses a wide composition range at high temperature. And the liquid and bcc phases extend to the Ni–Mn side and the region of bcc phase becomes longer and narrower with increasing temperature. A new ternary intermetallic compound (Ni, Mn)2Ga with the Mn2Ge-type hexagonal structure is present at 800 °C, but it disappears at 900 °C and 1000 °C. Based on the obtained information of phase equilibria, the composition dependence of martensitic transformation on the composition region of Ni2MnGa alloys was discussed. The present study may be useful for structural analysis and phase identification, as well as estimation of martensitic transformation temperatures of Ni–Mn–Ga alloys.

► Phase equilibria of Ni–Mn–Ga ternary system at 800 °C, 900 °C and 1000 °C are determined. ► A new ternary compound (Ni, Mn)2Ga with Mn2Ge-type hexagonal structure is present at 800 °C, but it disappears at 900 °C and 1000 °C. ► The composition dependence of martensitic transformation in the Ni–Mn–Ga ternary system is discussed.