Glass-forming ability of bulk Pd₄₀Ni₁₀Cu₃₀P₂₀ alloy

The partial replacement of Ni by 30 at%Cu for the Pd₄₀Ni_40-xCu_xP₂₀ alloys was found to cause the drastic increase in the glass-forming ability as is evidenced from the decrease in the critical cooling rate for glass formation (R_c) to 1.5 K/s and the increase in the critical sample thickness for glass formation (t_max) to 40 mm. The Pd₄₀Ni₁₀Cu₃₀P₂₀ amorphous alloy exhibits the distinct glass transition, followed by the appearance of a wide supercooled liquid region (ΔT_x(=T_x-T_g) reaching 95 K and then a single-stage crystallization. The differential thermal analysis indicates that the Pd-Ni-Cu-P alloy has a single stage melting reaction at 804 K. The resulting T_g/T_m is measured to be as high as 0.72. Considering that the R_c, t_max, ΔT_x and T_g/T_m are 128 K/s, about 7 mm, 63 K and 0.66, respectively, for a Pd₄₀Ni₄₀P₂₀ amorphous alloy with the largest glass-forming ability in previously reported Pd-based alloys, the present new Pd-Ni-Cu-P amorphous alloy is concluded to have a much larger glass-forming ability and a higher thermal stability of the supercooled liquid. The crystallization occurs through a single stage due to the precipitation of more than four kinds of crystalline phases and hence the necessity of long-range rearrangement of the constituent elements for the progress of the precipitation seems to cause the large glass-forming ability and the high thermal stability of the supercooled liquid through the retardation of crystallization. The finding of the new Pd-based amorphous alloy with the much larger glass-forming ability is important for the future development of basic science and engineering application of amorphous alloys.