Austenite avalanche evidenced by uniaxial stress in Ni-Mn-In Heusler single crystal

The martensitic transformation in Ni50Mn34.5In15.5 single crystal was studied by electrical resistivity measurements under controlled and constant uniaxial stress. We observed that the kinetics of the transformation under uniaxial stress, defined as the derivative of the volume fraction of martensite (austenite) with respect to time, present two maxima during heating at a constant rate of 3 K/min. An additional energy is required for the complete transformation to happen and there is a distortion in the hysteretic cycle depending on the rate. The interaction between transformed volume and untransformed volume and inter-variant conversion could be responsible for this distortion adding a local internal stress in the material. The transformation during heating is consequently isothermal. However, a new increase of the austenite restoration rate occurs in an avalanche form when additional superheating leads to an increase in the driving force that does not compensate any more the total strain energy.

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