OXIDATION AT DEFECTS IN SCALES ON IRON-CHROMIUM ALLOYS

A prior investigation on the lateral spreading of oxide into defects in Wustite scales on iron was extended to study the same phenomena in Fe-Cr alloys. Included were two Fe-Cr-Mo alloys and an Fe-25Cr-6Al alloy. Three types of experiments were conducted to study flaws introduced to simulate damage to protective oxide layers caused by particle erosion. It was found that outer scales of Wustite on the Cr-Mo alloys spread into flaws in much the same way as Wustite on unalloyed iron. However, inner scales of (Fe,Cr)3O4 on the Cr-Mo alloys and the scale formed on the Fe-25Cr-6Al alloy had only a slight tendency to spread into flaws. These results are consistent with the known higher diffusion coefficients and higher defect concentrations in Wustite than in other oxide phases.