The influence of coherent and semi-coherent TiCu precipitates on the martensitic transformation of melt-spun Ti50Ni25Cu25 shape memory ribbons

Abstract

Thin coherent as well as thicker semi-coherent plate-like precipitates of the same type, i.e. TiCu, were generated by different heat treatments of melt-spun Ti50Ni25Cu25 ribbons. Their influence on the martensitic transformation behavior was investigated by means of differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). It was found that thin coherent plate-like precipitates lower the temperatures of both martensitic and its reverse transformation and broaden the peak form of the DSC signal. On the other hand, thicker semi-coherent plates act to raise both transformation temperatures. The role of coherency stresses, arrangements of misfit dislocations, and compositional aspects are discussed.