Phase equilibria of Co-V-Ga ternary system and composition dependence of martensitic transformation characteristics in Co₂VGa Heusler alloys

The phase equilibria at 1000 °C of the Co-V-Ga ternary system and composition dependence of martensitic transformation characteristics in Co₂VGa Heusler alloys are investigated. Firstly, the results show that six three-phase regions and three ternary compounds are identified in the isothermal section. The CoVGa compound is discovered with a composition range of 43.0–46.2 at.% V and 27.3–31.4 at.% Ga. Secondly, according to the obtained phase equilibria, the martensitic transformation characteristics depending on composition for those alloys that locate the Co₂VGa Heusler phase region are investigated. The results confirm that the Co₂VGa Heusler phase exists in a wide composition range (about 39.7–66.5 at.% Co, 4.8–40.0 at.% V, and 15.0–31.2 at.% Ga). Furthermore, the critical compositions with the martensitic transformation temperature close to room temperature are determined, in which those alloys (50.8–58.5 at.% Co, 20.2–33.0 at.% V, and 15.2–21.5 at.% Ga) show the martensite structure at room temperature. Thirdly, based on the phase equilibria and the composition dependence of martensitic transformation characteristics, a Co₅₅V₂₄Ga₂₁ shape memory alloy is designed. Its microstructure, reversible martensitic transformation, and shape memory effect are investigated. Full shape recovery of about 2.6% is obtained. The present obtained results may provide useful information for composition designation and the estimation of martensitic transformation temperatures of Co-V-Ga Heusler shape memory alloys.