Phase transformations in melt-spun Ni-Mn-Ga alloys

The martensitic and magnetic phase transformations in several melt-spun ribbons prepared from Ni-Mn-Ga bulk alloys representing the three groups of Ni-Mn-Ga alloy compositions classified in [1] have been studied. Two essentially different quenching rates were applied to modify the transformation characteristics and shape memory properties of these alloys. A different behaviour of the thermally induced martensitic transformation (MT) for all as-received melt-spun ribbons and bulk materials was obtained, including changes of the martensitic modulated structures. The behaviour of the ribbons upon heat treatment in parent phase was also studied, resulting in the increase of MT temperatures (with constant hysteresis). Short range disorder retained after rapid quenching is proposed as a possible mechanism for the observed changes of martensitic and magnetic transitions.