Use of thermokinetic EMF and electrical resistance for quality control of elongated products made of shape memory alloy

摘要

The behavior of the thermokinetic EMF and electrical resistance upon nonstationary heating of the elongated TiNi wire samples with a near-equiatomic composition having sections subjected to elastic and plastic deformation was studied. It was found that the thermokinetic EMF value sharply increases in the deformed zone in the 1st thermal cycle with the movement of the heating zone along the sample. The increase in the relative deformation from 1 to 30% leads to a change in thermokinetic EMF (|ΔE|) from 0.01 to 0.37?mV. If the sample undergoes deformation up to 2%, the thermokinetic EMF value in the deformation area corresponds to the value on the nondeformed section during the 2nd thermal cycle. The value of |ΔE| is increased by 0.1?mV during deformation from 2 to 10% and is not changed with an increase in deformation up?to?30%. The behavior of the electrical resistance is similar to the behavior of the thermokinetic EMF when the heating zone moves along the length of the Ti-50?at.%?Ni wire sample in deformed zone from 2?to 15%. The electrical resistance increases sharply upon the 1st thermal cycle in the deformation zone. The electrical resistance increases by 25?μΩ?·?cm with an increase in the applied deformation up?to?15%. The value of electrical resistance does not change in the zone of deformation up?to?2% upon the 2nd thermal cycle. When the value of applied deformation falls in the range from 5?to 15%, the electrical resistance falls by 5?÷?20?μΩ?·?cm. Deformation of the Ti-50?at.%?Ni sample leads to a change in the properties of the alloy in the deformation zone, causing a shift in the characteristic temperatures of the phase transition and a change in the thermokinetic EMF and electrical resistance when the heating zone passes through the deformation zone. Changes in the thermokinetic EMF and electrical resistance as the heating region passes through the deformation zone are associated with a change in the characteristic temperatures of the phase transition. Based on the experimental data, a method and devices for determining inhomogeneous areas in elongated products made of shape memory alloys were developed. The method allows the value of thermokinetic EMF or electrical resistance to be continuously recorded during winding the wire when its section is heated above the temperature of the reverse phase transition. Tracking the change in the thermokinetic EMF or electrical resistance, it is possible to determine the sections of the material, which differ in physical properties from the predeterminated properties.