The Effect of Y Addition on Oxidation Resistance of Bulk W-Cr Alloys

The self-passivating tungsten-based alloy W-11.4Cr-0.6Y (in wt.%) is a potential plasma-facing material for the first wall of future fusion reactors, which has been shown to suppress oxidation of tungsten and withstand temperatures of up to 1000 °C. In this study, the effect of Y addition on the microstructure and oxidation behavior of W-11.4Cr alloy at 1000 °C is analyzed by comparing it with W-11.4Cr-0.6Y, both prepared using identical synthesis routes. While the binary W-Cr alloy already exhibits improved oxidation resistance over pure W due to the formation of an outer Cr2WO6 layer, it still shows a tendency for spallation and, hence, is not protective. A continuous passivating chromia layer is only obtained with the addition of Y, and we demonstrate that it results in a 50-fold decrease in the oxide growth rate and eliminates the preferred growth of the oxide at edges seen in the binary alloy. Although a porous, complex oxide scale containing mixed oxide layers and WO3 is formed in both cases, the addition of Y results in lower porosity, which makes the oxide scale more adherent.