Isothermal martensitic transformation in polycrystalline Ni sub(50)Mn sub(29)Ga sub(21)

The isothermal transformation behaviour of polycrystalline Ni sub(50)Mn sub(29)Ga sub(21) magnetic shape memory alloy is investigated by measuring the saturation magnetisation as a function of time and temperature. The results are analysed within the framework of the Johnson-Mehl-Avrami-formalism. The samples were prepared by directional solidification with a [inline image]1 0 0[inline image] texture of the high temperature cubic phase parallel to the heat flow. The samples were heat treated for chemical homogenization and stress relaxation in the austenitic state. They show a thermal hysteresis of martensite to austenite and the reverse transformation. The hysteresis becomes smaller with increasing measurement time. Grain boundary nucleation is a time controlling mechanism during the isothermal transformation in a constant magnetic field in these alloys.