Influence of anisotropy, the latent heat and the thermal history of alloy on martensitic transformation strain in Ni3Ta single crystal

Transformation characteristics in the single crystal of Ni3Ta shape memory alloy were studied by the dilatation measurement in the temperature range of room temperature up to 500 °C. The transformation strains were positive in the direction of the b-axes and the c-axes and negative in the direction of a-axes. The martensitic phase transformation takes place without volume change of the sample. Thermal diffusivity of the single crystal measured in two directions b-axes and a-axes was higher than that for polycrystalline material.The latent heat of the martensitic phase transformation influences the temperature distribution inside sample. Absorption (releasing) of the latent heat during heating (cooling) leads to cooling (heating) of the sample in place where the phase transformation takes place. This decrease (increase) of the temperature in the interface between both phases leads to stopping of the phase transformation. This effect is visible on the temperature dependence of the dilatation characteristics. The martensitic phase transformation in Ni3Ta single crystal took place with hysteresis of 30 °C. This hysteresis changes depending on the thermal history of the sample. Hysteretic behaviour of the Ni3Ta single crystal was analyzed and compared with behaviour of Ni53.6Mn27.1Ga19.3 alloy where no hysteresis was found.

► The thermal properties of the Ni3Ta single crystal are presented.
► Anisotropy of the thermal expansion characteristics and the thermal diffusivity is shown.
► Influence of the latent heat on the temperature distribution in the sample during the martensitic transformation is discussed.