Quantitative evaluation of critical cooling rate for metallic glasses

Abstract Evaluation of critical cooling rate R c for glass formation was carried out quantitatively for metallic glasses. A fundamental equation proposed for oxide glasses was modified for metallic glasses. In the calculation both Gibbs free energy of the molten alloys and the effect of the differences in atomic size were taken into account. The calculation was carried out for three groups: pure metals, typical glass-forming systems, and the latest metallic glasses with a large glass-forming ability found after 1990. The calculated results were in agreement with previous data. As examples, the R c for Ni metal, Co- and Pd–Cu-based metallic glasses in the present work were 9.1×10 8 , 1.2×10 5 and 1.6×10 −2 K/s , respectively, instead of 3×10 10 ,3.5×10 5 and 1×10 −1 K/s in the previous work. The following points are clarified: (1) T m 2 / η characterizes R c as is typical for the Pd–Cu-based metallic glass with a low melting point as well as high viscosity at the melting point; (2) negative heats of mixing and atomic size mismatch above about 12% affect the reduction of R c from 10 −2 to 10 −7 and from 10 −1 to 10 −2 ; and (3) the reduction of R c is understood as a stabilization of liquid state.