Oxidation of Zr-based metallic glasses and nanocrystalline alloys

Oxidation kinetics of bulk Zr-based metallic glasses seems to be controlled by oxygen diffusion through the scale towards the ZrO2/glass interface. Two modes of oxidation were observed: depending on the alloy either: (1) relative slow growth of homogeneous scales consisting of nodules or lamellae of tetragonal ZrO2 embedding nanocrystals of the late transition metals or (2) formation of fast growing oxide cones exhibiting a lamellar structure of the tetragonal and the less dense monoclinic ZrO2 thus allowing very fast oxygen diffusion along the interfaces between the lamellae. For both modes an influence of surface preparation on the oxidation reactions has to be mentioned. In addition, the oxidation behavior of these metallic glasses was compared with that of nanocrystalline or coarse crystalline alloys of similar composition. Whereas nanocrystallization improves the oxidation resistance of many Zr-based metallic glasses, coarse crystalline structures promote fast oxidation along grain boundaries, at least in Zr2Pd. (c) 2006 Elsevier B.V. All rights reserved.