Abstract
It is known that a thermokinetic electromotive force (EMF) in TiNi is induced due to thermoelastic phase transformations in a local zone. The initiation of these transformations is possible during the movement of both the local heating and cooling zones along a TiNi alloy sample. Local heating of the conductor results in a reverse phase transfomation (T≥Аs), while cooling results in a direct phase transfomation (T≤Мs). Since the amount of the martensite phase in TiNi based materials is determined by the temperature of a sample, it has been assumed that the value of thermokinetic EMF depends on the temperature in the heating zone too. Therefore, the aim of the present work was to determine the dependence of the thermokinetic EMF on heating temperature. In this paper, we propose a physical model, in which the thermokinetic EMF is initiated as a result of the potential difference in areas with direct and reverse phase transformations. These areas occur during the motion of a heating zone (T>As) along the TiNi alloy. Mathematical relationships which allow for a calculation of thermokinetic EMF initiated by reverse phase transformation in TiNi alloys and its dependence on temperature in the heating zone have been obtained. It has been found that thermokinetic EMF is induced when alloy temperature in the heating zone reaches As and then grows to 0.23 mV with increasing of alloy temperature up to Af. A further increase of the heating zone temperature does not affect the value of thermokinetic EMF. The results of calculations of thermokinetic EMF in TiNi alloys during reverse phase transformation obtained are in good agreement with experimental data.
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