Extremely low critical cooling rates of new Pd-Cu-P base amorphous alloys

A new Pd₄₀Ni₁₀Cu₃₀P₂₀ amorphous alloy subjected to the B₂O₃ flux treatment was found to have a maximum thickness above 50 mm and a low critical cooling (R_c) of 0.100 K s_-1. The R_c for the Pd-Ni-Cu-P alloy without the flux treatment is 1.58 K s^-1 and the decrease in R_c is due to the suppression of heterogeneous nucleation, in addition to the high T_g/T_m of 0.72 and ΔT_x(= T_x-Tg) of 98 K. These R_c values are smaller and the T_g/T_m and ΔT_x values are larger as compared with those (R_c = 140 K s^-1, T_g/T_m = 0.67 and ΔT_x = 63 K) for an unfluxed Pd₄₀Ni₄₀P₂₀ amorphous alloy. The new alloy appears to lie around the eutectic point with a low T_m of 804 K and the crystallization occurs through a single stage accompanying the precipitation of Pd₂Ni₂P, Pd₁₅P₂, (Ni, Cu)₃P and unknown compound. The finding of the new amorphous alloy with the lowest R_c and the largest thickness is important for the future development of bulk amorphous alloys.