Oxidation behaviour of Al-alloyed ZrSi2 at 700°C

The oxidation resistance of ZrSi₂-4 at.% Al prepared by reaction sintering was evaluated in air at 700°C. Two different stages were distinguished. In the first regime the oxidation rate remains high whereas the second one is characterised by a marked decrease on the oxidation rate. Passage from the first to the second stage, associated with a transition stage, is determined by the formation of a continuous protective alumina-rich layer at the scale/alloy interface. An oxidation mechanism is proposed to explain the different stages occurring through the oxidation. Grain boundaries contribute to the fast inward oxygen transport into the alloy, leading to internal oxidation of non-reacted silicon and aluminium during the reactive sintering stage of the processing. Oxidation resistance could be improved by increasing the grain size of the alloy and by using an appropriated processing method addressed to minimise or suppress the presence of silicon and aluminium particles at ZrSi₂ grain boundaries.