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

Thin coherent as well as thicker semi-coherent plate-like precipitates of t he same type, i.e. TiCu, were generated by different heat treatments of mel t-spun Ti50Ni25Cu25 ribbons. Their influence on the martensitic transformat ion behavior was investigated by means of differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). It was found that thin c oherent 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 transfor mation temperatures. The role of coherency stresses, arrangements of misfit dislocations, and compositional aspects are discussed.