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This paper discusses the application of rapid solidification by the melt-spinning method for the preparation of thin NiTi-based ribbons. Generally, the application of rapid solidification via melt-spinning can change the microstructure, improving the ductility and shape memory characteristics and lead to small-dimensioned samples. Several thousand thermal cycles were performed on the trained ribbons using bending deformation procedure, continuously observing the changes in the shape memory and transformation behaviors. These changes are due to the appearance of an intermediate phase which was stabilized probably by the accumulation of defects introduced by thermomechanical training. The influence of training and thermal cycling on characteristics of ribbons was studied by x-ray diffraction and transmission electron microscopy and differential scanning calorimetry. The results displayed that bending training methods were useful in developing a two-way shape memory effect (TWSME). All samples show a shape memory effect immediately after processing without further heat treatment. The addition of copper in NiTi alloys was effective to narrow the transformation hysteresis. The W addition has improved the stability of the TWSME and mechanical properties. The TWSME of ribbons and its stability are well suited for important applications such as microsensors and microactuators.

Quenching rates, in terms of circumferential wheel speed in melt-spinning, play an important role in the resultant characteristics of the ribbons. In this study, the influence of various wheel speeds on ribbon dimensions, cross-sectional microstructures, and crystallographic phases within samples were investigated. The Ni-50.3at.%Ti melt-spun ribbons were produced under 200 mbar He atmosphere at wheel speeds of 5-30 ms−1 using a quartz crucible coated internally with Y2O3. The different wheel speeds led to different sample dimensions and cooling rates. The microstructures of the samples were observed using optical microscopy and TEM, while the shape memory effect of samples and the existing phases were studied by differential scanning calorimetry, x-ray diffraction, and tensile tests.