Microstructure characterisation of directionally solidified MnNi damping alloy under strong magnetic field

Abstract

In order to reveal the effect of the magnetic field on the microstructure and the martensitic transformation of directional solidified MnNi alloy, four specimens were prepared by applying different magnetic fields during the directional solidification. The results show that the external magnetic field induces the formation of α-Mn phase, changes the orientations of dendrites as well as increases the dislocation density. The external magnetic field eliminates the fco→fct2 phase transformation and retains the fct→fcc transformation, meanwhile has little effect on the antiferromagnetic transition. The internal friction from twin boundary and phase transformation of directionally solidified MnNi alloy is 3–4 times that of as-rolled MnNi alloy, showing excellent high damping capacity in a wide temperature range.