Air-oxidation of a Pd40Ni40P20 bulk glassy alloy at 250–420 °C

Abstract

The oxidation behavior of a Pd40Ni40P20 bulk-metallic glass (Pd3-BMG) was studied over the temperature range of 250–420 °C 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 (kp 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.