Microstructure and texture development in Ti50Ni25Cu25 melt-spun ribbon

The conventionally produced Ti50Ni50-xCux shape memory alloys with Cu-content exceeding 12at.% have been reported to be brittle. The authors have recently reported that, after being properly annealed, the Ti50Ni25Cu25 melt-spun ribbon exhibits excellent superelasticity and shape memory effect. The present research aims to elucidate why these beneficial properties come about by investigating the evolution of microstructures and textures as a function of the annealing condition. It is found that annealing at 500 deg. C and above results in the formation of a strong (111)[7-bar 15]B19 sheet texture that is favorable to martensite detwinning, while with annealing at 550 deg. C and above the formation of B11 precipitates becomes significant. These two factors are believed to play key roles in determining the properties of the ribbon