Oxidation behaviour of Zr-1.7Sn-2.3Hf alloy in nitrogen-containing steam at 1200 ºC

The effect of nitrogen on the oxidation of Zr-1.7Sn-2.3Hf alloy in steam at 1200 °C was studied with respect to the oxidation kinetics and the underlying mechanism. Oxidation of Zr-1.7Sn-2.3Hf in steam obeys parabolic rate law regardless of the presence of nitrogen. Nitrogen, however, linearly accelerates the oxidation of Zr-1.7Sn-2.3Hf when its partial pressure exceeds a critical value. The accelerated oxidation of Zr-1.7Sn-2.3Hf is attributed to the cracks in the oxide layer caused by nitrogen. To account for the cracks, a new mechanism involving nucleation, growth and re-oxidation of ZrN precipitates was proposed.