Crystallization and grain refinement of Ti-30Ni-20Cu (at%) alloy ribbons prepared by melt spinning

Highlights: ► We fabricated amorphous Ti-30Ni-20Cu (at%) ribbons by melt spinning. ► Crystallization occurred in the sequence of amorphous–B2–Ti(Ni,Cu)2. ► Ti-30Ni-20Cu (at%) alloy ribbons with an average grain size of 0.25 μm were obtained by two-step annealing method. ► We confirmed that grain refinement caused the perfect shape memory recovery under the applied stress of 400 MPa. -- Abstract: Crystallization behavior of amorphous Ti-30Ni-20Cu (at%) alloy ribbons and martensitic transformation behavior, shape memory effect and superelasticity of crystallized ribbons were investigated by means of X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, thermal cycling tests under constant load and tensile tests. Crystallization occurred in the sequence of amorphous–B2–Ti(Ni,Cu)2 and the activation energy for crystallization of the B2 phase was 198.8 kJ/mol. Average grain size of the sample annealed in two-step, i.e., annealing at 773 K for 40 s followed by annealing at 748 K for 3.6 ks was 0.25 μm, which was very small comparing with the sample annealed in one-step, i.e., annealing at 823 K for 3.6 ks (1.20 μm). Grain refinement reduced the heat of transformation (ΔH) associated with the B2–B19 transformation and increased the critical stress for slip deformation causing the perfect shape memory recovery under the applied stress of 400 MPa