Effect of Thermally-Induced Surface Oxidation on the Mechanical Properties and Corrosion Resistance of Zr60Cu25Al10Fe5 Bulk Metallic Glass

The electrochemical corrosion resistance (in NaCl solution) and mechanical behavior of Zr60Cu25Al10Fe5 metallic glass are modified by the controlled growth of a protective oxide coating, with tunable thickness, during air-annealing treatments in the temperature range 573-673 K. The oxide layer is mainly composed of ZrO2 and Al2O3 and is depleted in Cu and Fe oxides. The glassy structure of the as-cast Zr60Cu25Al10Fe5 alloy is preserved underneath the coating after annealing at 623 K whereas partial crystallization occurs at 673 K. The corrosion current density decreases while the size of the capacitive loop in Nyquist diagrams increases as the oxide layers are made thicker. Nanoindentation experiments reveal an increase of hardness, H, reduced Young's modulus, E-r, and H/E-r ratio (indicative of wear resistance) after oxidation. Oxidation at 623 K results in an optimum mechanical behavior probably due to the nature of the constituent phases, which can be useful for applications where different parts have to operate in contact.