Thermokinetic EMF during a reverse phase transition in titanium nickelide as a way of information recording

Abstract

The external factors that influence on the thermokinetic EMF value in the Ti – 50 at.% Ni samples were determined. A method for setting thermokinetic EMF in certain sections of the TiNi wire was developed. The thermokinetic EMF value was measured directly using a digital millivoltmeter MNIPI V7-72. The sections of the Ti – 50 at.% Ni wire samples were subjected to tensile tests on a tensile machine IP 5158-5. On the basis of calorimetric studies, the kinetics of martensitic transformations was investigated. It was found that the direct phase transition affects the thermokinetic EMF value of the Ti – 50 at.% Ni during thermal cycling. Thermal cycling in the temperature range of the complete martensitic transformation causes the thermokinetic EMF value reduction by 0.16 mV by the 15^th temperature cycle. The degradation of the thermokinetic EMF value by 0.04 mV took place during thermal cycling in the temperature range of the incomplete martensitic transformation by the 70^th thermal cycle. The thermokinetic EMF value was restored to 0.22 mV with increasing temperature to 240 °С, as in the case of annealing at temperatures of 400÷800 °С. The thermokinetic EMF value is associated with a change in physical and mechanical properties of the alloy during thermal cycling. It is characterized by a change in stages of the phase transition and a shift of the characteristic temperatures. On the basis of the obtained experimental data, a method was proposed for a purposeful setting of extended TiNi wire sections with the thermokinetic EMF value from 0 to 0.6 mV, using different methods of influence on its value (thermal cycling, deformation, temperature change in heating zone). The proposed technical solution can be used as a method for information recording.