Temperature dependence of the damping properties of Ni–Mn–Ga alloys

Single-crystalline 5M (exhibiting magnetic shape memory effect) and non-modulated martensitic Ni–Mn–Ga alloys were studied by dynamic mechanical analysis (DMA) at different temperatures. The chemical compositions of the alloys were determined using energy-dispersive X-ray spectrometry in a scanning electron microscope. The crystal structures were confirmed with X-ray diffraction and the transformation temperatures were measured. DMA measurements showed that the mechanical modulus (stiffness) and damping capacity increased during heating and a clear peak of the loss angle, was detected which is related to the reverse phase transformation of martensite to austenite. During cooling, there is a corresponding peak related to the martensite reaction. Significant decrease of the damping capacity occurs during transformation to austenite. Enhanced damping in the martensitic phase can be attributed to the mobility of twin boundaries.