Shape memory effect in Ti-Ta-Zr alloys

Abstract

The degree of recoverable strain, reactive stress and pseudoelasticity of some Ti-Ta-Zr alloys were investigated. The measurement technique involved differential calorimetry, estimation of friction and evaluation of recoverable torsion strain. The alloys were quenched from different temperatures of the β-phase area and subjected to additional thermal and mechanical treatment required for subsequent examination. The degree of recoverable strain was measured on custom-made unit. The samples have been heated by electrical current and using a furnace. Initial deformation of the specimens was achieved by torsion. For all of the alloys the shape recovery was not less than 90–98% for initial strain up to 7–9%. M _{s} and A _{s} values for the alloys range in 298–433 K and 523–673 K interval. These allowed to conventionally consider the shape memory effect in these alloys as a "high temperature" (respectively to TiNi) phenomenon. The values of the reactive stress induced by reverse martensite transformation in the alloys was measured to be 300–550 MPa. After 3–4 cycles the pseudoelasticity of the alloys (strain-stress cycled at room temperature), for the initial strain– 3.5–4%, comes up to 100%.