Air-oxidation of a Pd₄₀Ni₄₀P₂₀ bulk glassy alloy at 250-420 ºC

The oxidation behavior of a Pd₄₀Ni₄₀P₂₀ bulk-metallic glass (Pd3-BMG) was studied over the temperature range of 250-420 ºC in dry air. The Pd3-BMG revealed nearly no oxidation at T < 300 °C, while its oxidation kinetics followed a multiple-stage parabolic-rate law at T ≥ 300 °C, with its oxidation rates increasing with temperature. In general, the oxidation rate constants (k_p values) of Pd3-BMG are slightly higher than those of the crystalline counterpart and polycrystalline pure Ni at 300-420 °C, indicating that the amorphous alloy exhibited a poor oxidation resistance. An exclusive layer of NiO scale formed on the alloy surface and a Pd-enriched layer was also observed beneath the scale. In addition, the amorphous substrate transferred into two crystalline phases of Pd₃P and Ni₃P after the oxidation at T ≥ 300 °C, indicative of the occurrence of phase transformation.