Oxidation resistance of nanocrystalline vis-à-vis microcrystalline Fe–Cr alloys

This paper investigates the hypothesis that nanocrystalline structure may confer considerable oxidation resistance to iron–chromium alloys at much lower chromium contents. Discs of nanocrystalline Fe–10%Cr alloy were produced by ball milling of Fe and Cr powders and compaction of the powder without considerable grain growth (by processing within a suitable time–temperature window). Corrosion resistance of discs of nanocrystalline and microcrystalline alloys was compared by subjecting them to oxidation in air and post-oxidation characterisation of the oxide scales by secondary ion mass spectroscopy (SIMS). Nanocrystalline Fe–10%Cr alloy showed considerably greater oxidation resistance than the microcrystalline alloy of the same composition. Chromium content of the inner scale formed over the nanocrystalline alloy was detected to be nearly five times greater than that in the case of microcrystalline alloy, facilitating formation of the passive layer and providing an explanation for the greater oxidation of the former.