Thermo-mechanical Phase Transformation of Rapidly Quenched Ti-Ni-Cu Ribbons

The thermo-mechanical transformation (i.e., the shape memory effect (SME)) of a rapidly quenched Ti-Ni-Cu alloy was investigated. Some comparisons in the properties with the phase transformation (i.e., transformation temperature, thermal hysteresis, its stress dependence, ability of energy conversion, etc.) were done between rapidly quenched (RQ) Ti₅₀Ni₄₀Cu₁₀(at%) ribbons and conventional polycrystalline Ti₅₀Ni₄₀Cu₁₀, Ti₅₀Ni₅₀(at%) wires. The self-deformation associated with the phase transformation (i.e., SME) in the RQ ribbons was 3-4 times larger than that of the conventional poly crystalline alloy wires, and the hysteresis curve of strain vs temperature was narrow in shape and changed sharply at the transformation points under increasing applied stress. Since the RQ ribbons became smaller in self-defor-mation and broader in hysteresis loop by annealing at 973 K, the inferiority of SME in the recrystallized structure with grain nucleation, subsequent grain growth and lower dislocation density was confirmed. From the characterization of the conversion from thermal energy into mechanical energy, the RQ material has more efficient energy conversion ability than the recrystallized polycrystalline materials. More superior characteristics in SME will be anticipated in the microstructural region produced by more rapid solidification control.