•Nancy Boucharat, Harald Rösner und Gerhard Wilde
Forschungszentrum Karlsruhe, Institut für Nanotechnologie, Postfach 3640, 76021 Karlsruhe
Amorphous Ti50Ni25Cu25 melt-spun ribbons crystallize polymorphously in spherical grains upon heating. Since the growth proceeds isotropic and partitionless, this ternary alloy is an ideal candidate for applying various models to describe the nucleation and growth kinetics near the glass transition. Therefore, the crystallization processes have been studied by calorimetry in isothermal and isochronal modes in conjunction with structural analyses and have been compared to theoretical model predictions. The experimental results show that the entire crystallization transformation can be adequately described by the Johnson-Mehl-Avrami-Kolmogorov (JMAK) kinetics model for three-dimensional isotropic growth. Moreover, detailed investigations in TEM have been conducted to monitor the microstructure at different stages of the crystallization reaction. The impact of the various thermal treatments on the shape memory behavior is discussed in terms of considerable microstructure changes of the resulting product.