The influence of composition and thermomechanical treatments on the magnetic shape memory effect of Ni-Mn-Ga single crystals

摘要

In the current work, repeated mechanical and magnetic forces have been applied to Ni-Mn-Ga samples with different compositions and different thermomechanical histories in order to determine the combined effects of these parameters on the magnetic shape memory effects, especially the magneto-mechanical properties, of these alloys. The results demonstrate that prior history has strong influence on the twinning start stress and twinning strain. In addition, heat treatment of the materials seems to increase the amount of strain that can be obtained (up to the theoretical limit). Moreover, there is indication that prior heat treatment may also affect the martensite crystal structure that is formed during cooling. In addition, the dependence of martensitic transformation on composition and prior thermomechanical treatments was also studied by differential scanning calorimetry (DSC) analysis.