Crystal Nucleation and Growth in Glassy and Liquid Pd40Ni40P20

Abstract

AbstractTurnbull pointed out that good glass formability should correlate with a high reduced glass transition temperature, Trg. The alloy Pd40Ni40P20 has an unusually high Trg of ∼0.66 and indeed it can be formed into a glass at rather low cooling rates (≲ 1 Ks−1 ). In this paper a number of experiments are described which take advantage of the high resistance to crystallization in this alloy to study behavior in the labile temperature range between Tg and Tm. The anomalously low crystal growth velocities arise because the product is a three phase mixture. Nucleation kinetics are derived from crystal size distribution analysis. Heterogeneous nucleation at the surface of melt spun ribbon is characterized; significant surface relief develops on crystallization because of the low number of nuclei. In bulk glass produced by fluxing, good crystal size statistics show that internal nucleation is predominantly also heterogeneous, but with a significant transient time. Measurements of the specific heat of the undercooled liquid reveal that the free energy of crystallization deviates significantly from a linear dependence on undercooling (expected for pure metals) in the way predicted by Dubey and Ramachandrarao.