Flux treated Pd-Cu-Ni-P amorphous alloy having low critical cooling rate

A Pd40Cu30Ni10P20 alloy subjected to B2O3 flux treatment was found to have a low critical cooling rate (R-c) of 0.100 K/s for glass formation and a large sample thickness (t(max)) of 72 mm by the water quenching process. The R-c and t(max) exceed largely those (R-c = 1.57 K/s, t(max) = 40 mm) for the Pd-Cu-Ni-P alloy without the flux treatment. It is concluded that the flux treatment causes a significant increase in the thermal stability of the supercooled liquid. The glass transition temperature (T-g) remains unchanged in the fluxed state, but the crystallization temperature (T-x) increases by 7 K, leading to the extension of the supercooled liquid region defined by Delta T-x (= T-x-T-g) to 98 K which is larger than that (91 K) for the non-fluxed sample. The decrease in R-c and the increases in t(max) and Delta T-x for the fluxed sample are presumably due to the suppression of heterogeneous nucleation for crystallization resulting from the increase in the degree of cleanness of the molten alloy. Besides, the Pd-Cu-Ni-P amorphous alloy has lower R-c and melting temperature (T-c) and larger t(max), Delta T-x and T-g/T-m values, as compared with those for Pd40Ni40P20 alloy. The larger glass-forming ability for the Pd-Cu-Ni-P alloy is presumably due to the increase in the degree of the satisfaction of the three empirical rules for the achievement of larger glass-forming ability resulting from the more systematic change in atomic size in the order Pd much greater than Cu > Ni much greater than P and the generation of Cu-Pd and Cu-P atomic pairs with negative heats of mixing. There is no appreciable difference in the T-g, T-x and crystallization behavior between the cast 72 mm(phi) amorphous ingot and melt-spun amorphous ribbon. The finding of the fluxed Pd40Cu30Ni10P20 alloy with the lower R-c and larger t(max) values is promising for the future development of bulk amorphous alloys.