Martensitic Transformations of Ni_(54)Mn_(25)Ga_(21-x)Al_x Shape Memory Alloys

摘要

The non-stoichiometric NiMnGa shape memory alloy with high Ni content has been developed as promising thermo-actuated materials applied at high temperature. A substitution of Al for Ga in the Ni_(54)Mn_(25)Ga_(21) alloys is performed. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) measurements have been carried out to study the effects of the phase transformations and microstructures of the Ni_(54)Mn_(25)Ga_(21-x)Al_x shape memory alloys. The results show that the martensitic transformation temperatures almost linearly decrease with the increase of Al substitution for Ga, which can be explained considering the effect of the size factor, i.e. the lattice parameter. A structural transition from a non-modulated tetragonal type to a seven-layered 14M one has been found during the increase of Al substitution for Ga.