An Enhanced Three-Step Oxidation Process to Improve Oxide Adhesion on Zirconium Alloys

Oxidation of zirconium-based alloys results in a thermally-grown oxide scale with excellent corrosion resistance, and good wear and friction properties, which make them interesting for tribological applications. Nevertheless, adhesion of the oxide layer to the substrate must be enhanced. A new three-step oxidation process was introduced in order to achieve an improvement. Following an initial oxidation step (1st step), a heat treatment was carried out in vacuum during which the oxide dissolves and diffuses into the metallic zirconium substrate (2nd step). These two steps resulted in an oxygen dissolution layer with increased hardness formed in-between the oxide and the substrate, which serves as a bonding layer with increased thickness. In a 3rd step a new oxide layer was obtained. The improved oxide layer adhesion was characterized by indentation tests on three different groups of oxidized samples of the newly developed alloy.