Initiation of the shape memory effect by temperature variation or ultrasonic vibrations in the NiTi shape memory alloy after different preliminary deformation

The strain variations induced by conventional heating or ultrasonic vibrations in the Ni – 49.8 at.% Ti shape memory alloy after different preliminary deformation (from 5 to 30%) in the martensite state were studied. It was found that if the residual strain was 16% or less, then the shape memory effect value did not depend on the initiation method. The strain recovery was induced by ultrasonic vibrations during 20 s and occurred at lower temperatures than during conventional heating, due to partially suppression of the martensite stabilisation effect. The ultrasonic vibrations did not influence the plastic strain but they decreased the value of the two-way shape memory effect due to the dislocation rearrangement. The results of the study showed that the USVs might be successfully used for the initiation of the shape memory effect in actuators without heat sources.