The crystallization process, microstructure, martensitic transformation and mechanical properties of Ti-Ni-Zr alloy ribbons

In the present study, the Ti-Ni-Zr alloy ribbons with the various Zr contents were fabricated at the optimum process conditions. The crystallization process and the effect of the following annealing treatments on the microstructural evolution, martensitic transformation behavior, mechanical properties and shape memory effect of the annealed Ti-Ni-Zr alloy ribbons were investigated systematically. The results revealed that the phase constituents were dependent on the Zr contents, and can be tailored by the annealing treatment. The λ1 precipitate existed in all annealed Ti-Ni-Zr alloy ribbons and NiZr phase appeared only in the annealed Ti-Ni-Zr alloy ribbons with the Zr content more than 25 at.%. With the annealing temperatures increasing, the martensitic transformation temperature increase. And the Ti-Ni-Zr alloy ribbons with the higher Zr content showed the relatively lower transformation temperatures owing to the presence of the NiZr precipitate. The nano-scale λ1 precipitate and NiZr phase can enhance the matrix strength and improve the mechanical properties, while the appearance of the lots of the NiZr phase would deteriorate the shape memory effect. Among, the annealed Ti-Ni-Zr alloy ribbon showed the excellent combination of the higher transformation temperatures, superior mechanical and strain recovery characteristics. In summary, the evolution of the microstructure containing the martensitic/austenitic state, type/size of the precipitate, and distribution state of the precipitate resulted in the changing of the martensitic transformation, mechanical properties and shape memory effect.