Effect of Ni excess on phase transformation temperatures of NiMnGa alloys

A systematic substitution of Ni for Mn, Ga, or both Mn and Ga in the non-stoichiometric NiMnGa alloys is performed. The relationship among the composition, structure and martensitic transformation temperatures was studied in detail for the Ni excessive NiMnGa alloys. The martensitic transformation temperatures almost linearly increase with increasing Ni content in all the three series from lower than 0 °C up to 300 °C. The increases in rate of the martensitic transformation temperatures are different for the three cases. It is large for Ga substituted by Ni, slow for Mn and intermediate for both Mn and Ga. The size factor and electronic concentrations are thought to influence the martensitic transformation temperature in the NiMnGa alloys. The determined relationship will be significant for designing a suitable NiMnGa alloy with a required martensitic transformation temperature for application at a specific temperature.