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

Abstract

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.