Effect of atomic structure on preferential oxidation of alloys: amorphous versus crystalline Cu-Zr

The effect of structural order in the parent alloy substrate on the oxidation kinetics and oxide phase evolution was investigated for the thermal oxidation of amorphous Cu33at.%Zr67at.% and crystalline CuZr2 alloys of identical compositions in the temperature range of 200–250 °C. It was found that, besides the strong preferential oxidation of Zr in both alloys, the lack of structural order in the amorphous Cu33at.%Zr67at.% alloy results in much slower oxidation kinetics, as well as in distinctly different microstructures of the oxide overgrowth and its Zr-depletion zone in the wake of the ZrO2 overlayer growth front. The experimental findings can be rationalized on the basis of the strikingly different atomic mobilities of Cu, Zr and dissolved O in the amorphous and crystalline alloys, which also results in different nucleation barriers for crystalline oxide nucleation. The thus obtained knowledge on the underlying oxidation mechanisms provides new and profound insights into the surface engineering of metallic alloys.