Martensitic transformation and mechanical properties of polycrystalline Ni50Mn29Ga21−xGdx ferromagnetic shape memory alloys

The aim is to investigate the influence of heavy rare earth Gd addition on the microstructure, martensitic transformation and mechanical properties of polycrystalline Ni50Mn29Ga21 shape memory alloy. It is shown that microstructure of the Ni–Mn–Ga–Gd alloys consists of the matrix and the Gd-rich phase. The Gd-rich phase firstly disperses homogeneously in the matrix with small amounts and then tends to segregate at the grain boundaries with the increase of Gd substitution for Ga. With increasing Gd content, the martensitic transformation temperatures increase remarkably and the grain size is reduced obviously. Different martensitic phase transformation appears in different Gd content. Martensite structure changes from 5 M with 0.1 at% Gd to 7 M when the content of Gd is more than 0.1 at%. It is revealed that the addition of Gd significantly enhances the bending strength and improves the ductility of the alloys. The mechanism of the improved mechanical properties is also discussed.