Two-Way Shape Memory Effect in Rapidly-Quenched High-Copper TiNiCu Alloys Deformed in the Martensitic State

Abstract

The effect of martensitic deformation on the two-way shape-memory effect (SME) of quasi-binary high-copper TiNi–TiCu alloys (with 25–40 at % Cu) is studied. The alloys are prepared by rapid quenching from the melt in an amorphous state in the form of ribbons 30–50 μm in thickness. The alloys crystallize during isothermal annealing, the time of which is varied from 100 to 300 s, and during a single current pulse 10 ms in duration. The relatively low bending strains (1.5–3%) are shown to cause two-way SME in TiNiCu alloys; as the strain of martensite increases, the reversible strain in the martensitic transformation range increases markedly. An increase in the copper content is found to cause a substantial decrease in the value of two-way SME, which is related to the formation of the brittle TiCu phase. At the same time, a decrease in the heat treatment time causes an increase in the reversible strain, which reaches the maximum value (2.35%) for the alloy with 25 at % Cu subjected to high-rate electric pulse treatment.