Thermomechanical effects on phase transformations in single-crystal Cu–Al–Ni shape-memory alloy

Abstract

Single-crystal rods of Cu–Al–Ni shape-memory alloy fabricated from a molten pool of 82 wt% Cu, 14 wt% Al, and 4 wt% Ni by the Czochralski method were first heated to ∼870 °C and then quenched to obtain austenitic microstructures. Various microanalysis techniques were used to determine the chemical composition, microstructure, and phase-transformation temperatures of the produced alloy. Cyclic tensile tests with in situ temperature control demonstrated the occurrence of pseudoelastic deformation at elevated and close to phase-transformation temperatures and provided insight into the temperature dependence of the phase-transformation stress, damping characteristics, and cyclic straining of single-crystal Cu–Al–Ni alloy. The stress hysteresis observed in the pseudoelastic deformation cycles decreased at elevated temperatures. The stress response at different temperatures is associated with the formation, growth, and coalescence of martensite variants. Stress-induced phase-transformation mechanisms, coalescence of twin variants, and energy dissipation by pseudoelastic deformation are discussed in the context of experimental findings. The results illustrate the potential of single-crystal Cu–Al–Ni as a structural material for dynamic microsystems and temperature sensors.