Optical microscopic study on NiCoMnAl metamagnetic shape memory alloy by in situ observation under a pulsed high magnetic field

Abstract

In situ microscopic study was carried out on Ni44.3Co 5.1Mn31.4Al19.2 metamagnetic shape memory alloy under a pulsed magnetic field up to 35.5 T. Magnetic field-induced reverse martensitic transformation was directly observed. The critical magnetic fields were determined from the contrast change of the microstructure, where good agreement had been found by magnetization measurement in a previous study. Comparison of the micrographs during thermal and magnetic field cycles between Ni45Co5Mn36.7In13.3 and Ni 44.3Co5.1Mn31.4Al19.2 was conducted. It is concluded that though the energy barrier related to thermal activation strongly effects the martensitic transformation of Ni45Co 5Mn36.7In13.3, its effect is very small on Ni44.3Co5.1Mn31.4Al19.2. Qualitative discussion yielded a reasonable understanding of the results of microstructure observation. © 2012 The Japan Institute of Metals.