Synthesis and characterization of Ni-Mn-Ga alloys with addition of Cu

Abstract

Non-stoichiometric Heusler Ni-Mn-Ga based alloys with addition of up to 7,5 at.% of Cu were prepared. Homogenized alloys were characterized using polarized light microscopy, X-ray diffraction, differential scanning calorimetry and differential thermal analysis, vibrating sample magnetometer analysis and nanoindentation. Results of polarised light microscopy have revealed that all the alloys prepared, either in as-cast or homogenized state, have martensitic microstructure. X-ray diffraction has proved that tetragonal non-modulated martensite is present in all homogenised alloys. In a sample with the highest addition of copper MnO was also found. Thermal analysis revealed that the Curie temperatures decrease with e/a concentration and temperatures of martensitic transformation increases with e/a concentration. It was also found that saturation magnetization has decreased with increasing copper content for the samples with Curie temperature above room temperature (samples with copper concentration up to 2,77 at.%). Nanoindentation experiments suggest that hardness and elasticity modulus are increasing with increasing copper content.