Oxidation behaviour of bulk W-Cr-Ti alloys prepared by mechanical alloying and HIPing

Self-passivating tungsten based alloys are expected to provide a major safety advantage compared to pure tungsten when used as first wall armour of future fusion reactors, due to the formation of a protective oxide scale, preventing the formation of volatile and radioactive WO3 in case of a loss of coolant accident with simultaneous air ingress. In this work results of isothermal oxidations tests at 800 and 1000 °C on bulk alloy WCr12Ti2.5 performed by thermogravimetric analysis (TGA) and by exposure to flowing air in a furnace are presented. In both cases a thin, dense Cr2O3 layer is found at the outer surface, below which a Cr2WO6 scale and Ti2CrO5 layers alternating with WO3 are formed. The Cr2O3, Cr2WO6 and Ti2CrO5 scales act as protective barriers against fast inward O2− diffusion. The oxidation kinetics seems to be linear for the furnace exposure tests while for the TGA tests at 800 °C the kinetics is first parabolic, transforming into linear after an initial phase. The linear oxidation rates are 2–3 orders of magnitude lower than for pure W.