Resistance of nanocrystalline vis-a-vis microcrystalline Fe-Cr alloys to environmental degradation and challenges to their synthesis

This paper presents a hypothesis and its experimental validation that a nanostructure can bring about dramatic improvements in the oxidation/corrosion resistance of iron-chromium alloys. More specifically, a nanocrystalline Fe-10 wt% Cr alloy was found to undergo oxidation at a rate that was an order of magnitude lower than its microcrystalline counterpart. Importantly, the oxidation resistance of nanocrystalline Fe-10 wt% Cr alloy was comparable with that of the common corrosion-resistant microcrystalline stainless steels (having 18-20 wt% chromium). The findings have the potential of leading to the next generation of oxidation-resistant alloys. However, due to poor thermal stability of nanocrystalline structure, synthesis/processing of such alloys is a challenge. 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. The paper also presents a theoretical treatise to arrive at the minimum chromium content required for establishing a protective layer of chromium oxide in an Fe-Cr alloy of a given nanometric grain size.