KINETIC AND THERMODYNAMIC ASPECTS OF CRYSTALLIZATION IN CU-TI-NI AND CU-TI-AL METALLIC GLASSES

Cu50T40Ni10 and Cu50Ti40Al10 alloys were amorphized by rapid solidific ation. Their crystallization kinetics was studied by differential scan ning calorimetry (DSC) and X-ray diffraction. Examples were found for different mechanisms according to the alloy composition and temperatur e range of the experiments. Cu50Ti40Ni10 crystallizes to nanocrystalli ne (Cu,Ni)3Ti2. In the neighbourhood of T(g) the activation energy is 236 kJ mol-1. Substantial incubation times are found and the Avrami co efficient always exceeds 4, indicating an increasing nucleation rate. Cu50Ti40Al10 crystallizes predominantly to a phase isomorphous with ga mma-CuTi with an activation energy of 328 kJ mol-1. The Avrami coeffic ient is around 3 and the incubation time is low. The process appears t o be controlled by crystal growth on a steady state population of nucl ei. A thermodynamic discussion of glass formation and crystallization is given with the help of data on the melting behaviour of the alloys obtained by high temperature DSC.