Flux Treated Pd–Cu–Ni–P Amorphous Alloy Having Low Critical Cooling Rate

Abstract

A Pd 40 Cu 30 Ni 10 P 20 alloy subjected to B 2 O 3 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 (Tg) 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 ΔT 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 Δ 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 m ) and larger t max , ΔT x and T g / T m values, as compared with those for Pd 40 Ni 40 P 20 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 » Cu > Ni » P and the generation of Cu-Pd and Cu-P atomic pairs with negative heats of mixing. There is no appreciable difference in the Tg, T x and crystallization behavior between the cast 72 mm Φ amorphous ingot and melt-spun amorphous ribbon. The finding of the fluxed Pd 40 Cu 30 Ni 10 P 20 alloy with the lower R c and larger t max values is promising for the future development of bulk amorphous alloys.