CRYSTALLIZATION OF CU50TI50 GLASSES AND UNDERCOOLED MELTS

Crystallization of melt-spun Cu50Ti50 ribbons was studied in detail by optical and electron microscopy. At rather low annealing temperatures surface-induced polymorphic crystallization of gamma-CuTi is finished prior to any crystallization in the bulk. Only a minor influence of the glass transition on the temperature dependence of crystal growth has been observed; the nucleation rate, however, is strongly affected by the glass transition as known from metal-metalloid glasses. In this temperature range an Arrhenius equation for nucleation assuming diffusion-controlled atomic transport would lead to rather unrealistic activation energies. Above the glass transition temperature, i.e. in undercooled melts, the atomic transport necessary for crystallization should be better described by viscous flow.