Thermodynamics of oxide formation in W-Cr-Y smart alloys
Tungsten is one of the primary materials for several applications in commercial fusion power plant designs, in particular for divertor targets and the first wall. In maintenance conditions or during a loss of coolant accident, tungsten is expected to reach temperatures at which it readily volatilises as tungsten trioxide in contact with air, potentially distributing radioactive material and posing a hazard to personnel. The production of W-Cr-Y ’smart’ alloys is currently being upscaled, which promises a highly effective alternative to pure tungsten first walls. Under oxidative conditions, W-Cr-Y alloys form a self-passivating layer of Cr2O3, the formation of which is aided by the incorporation of small amounts of yttrium. In this work, density functional theory is employed to obtain the enthalpy of formation of four major oxides which form during the oxidation of W-Cr-Y. Our results show that Y2O3 forms preferentially, especially from yttrium and oxygen which have been solvated in bulk tungsten, indicating that the yttrium plays an important role in binding oxygen to enable the migration of chromium through the bulk.