Diffusion mechanism of Zr-based metallic glass during oxidation under dry air

Oxidation kinetics of a Zr55Cu30Al10Ni5 bulk metallic glass (BMG) and its crystalline counterpart were studied under dry artificial air at 673 K for long oxidation duration by thermogravimetry analysis (TGA). Oxidation kinetics was observed to follow a parabolic-rate law for the crystalline counterpart and a three-stage behaviour for the BMG. The ionic diffusion mechanism was investigated by using a two-stage oxidation treatment (16O2 oxidation and then 18O2 oxidation). The evident solute penetration zone and ion diffusion characteristic through the oxide scale were determined by Cs+ secondary ion mass spectrometry (SIMS) depth profile. The results of ion evolution indicated that the oxide grew under concurrent inward oxygen and outward Zr diffusions in short-term stage of the BMG oxidation; and the oxidation kinetics was controlled mainly by outward Cu and inward O diffusions in the case of long-term oxidation process.