Synthesis and corrosion behavior of nanocrystalline Fe-Cr alloys

Rajeev Kumar Gupta
2017
Nanocrystalline (nc) materials, a single or multi-phase polycrystalline solids with a grain size of a few nanometers, typically less than 100 nm have attracted considerable attention of research community. However, investigation of corrosion/oxidation resistance of these materials has attracted limited research attention. Motivation of the current study is to understand the effect of nanocrystalline structure on the corrosion/oxidation resistance and to validate the hypothesis that passivity in
more » ... s that passivity in the Fe-Cr based alloys can be achieved at lower Cr content if the grain size is reduced to the nano level. However, to investigate the oxidation/corrosion resistance bulk samples of nc materials are required and preparation of bulk samples is not a trivial task. Current study presents a technique to prepare consolidated bulk samples of Fe-Cr based nc materials after a systematic study of grain growth and mechanical (hardness) behavior of nc Fe-10Cr alloys. Oxidation resistance of nc Fe-Cr alloys is compared with that of microcrystalline (mc) Fe-Cr alloys at various temperatures for a time period of up to 52 hours. Nanocrystalline Fe-Cr alloys showed considerably greater oxidation resistance than the mc alloys of the same compositions. This study presents novel results to prove that it is possible to develop a protective layer of chromium oxide at only 10 wt% chromium during oxidation of a nc Fe-Cr alloy. Thus the thesis provides evidence to validate the hypothesis that nc structure can confer considerable oxidation/corrosion resistance at much lower chromium contents (as compared to 18-20 wt% chromium in the common mc Fe-Cr alloys). Oxidation resistance of discs of nc and mc alloys was compared by subjecting them to oxidation in air, and post-oxidation characterization of the oxide scales by secondary ion mass spectrometry (SIMS). The thesis also presents a theoretical treatment 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 g [...]
doi:10.4225/03/587c0470c8ccc fatcat:5zqhb2gyiva6bmjqfzghzxsuwm