Effects of High Magnetic Field and Tensile Stress on Martensitic Transformation Behavior and Microstructure at 4.2 K in Fe–Ni–C Alloys

Abstract

Effects of high magnetic field and tensile stress on martensitic transformation behavior and microstructure at 4.2 K have been studied in Fe-31Ni-0.4C and Fe-27Ni-0.8C (wt%) shape memory alloys. In order to make clear the difference of the effects of high magnetic field and tensile stress on the amount of martensite, two types of experiments were conducted, that is, the magentic field of 10 T was applied first and then the tensile stress of 220 MPa was applied in constant magnetic field in one type of experiment and the tensile stress of 220 MPa was applied first and then the magnetic field of 10 T was applied under constant tensile stress in the other type if experiment. The amount of martensite formed in these two experiments were compared. It was found that the critical magnetic field to induce martensitic transformation is between 7.5 T and 10 T. In the case of Fe–27Ni–0.8C, martensitic transformation is stress-induced at lower level of stress in magnetic field than in the case no magnetic field is applied. The amount of martensite formed by increasing the magnetic field under constant stress is larger than that formed by increasing the stress in the constant magnetic field, which shows that the effect of tensile stress on the number density of martensite is larger than that of magnetic field in this experimental condition.