Oxidation behavior of a large variety of alloys has been studied for a wide range of conditions. The study examined commercial, heat resistant alloys, which are widely used in high-temperature, process equipment. The exposure conditions included temperatures of 473 – 1450 K, times of 500 – 24,000 hr, and O2 concentrations of 0.1-100% volume in O2-N2 mixtures at one atmosphere total pressure. The traditional method of reporting oxidation by weight change/area was found to measure only 10-20% of the metal penetration by oxidation for many of the alloys. Most of the alloys resisted oxidation by formation of a surface layer rich in Cr2O3 and experienced the majority of metal penetration by internal oxidation or void formation. However, surface scale formation was the cause of nearly 100% of the metal penetration for the alloys which formed scales rich in Al2O3 and, surprisingly, additional exposure time did not induce additional oxidation. These Al2O3 – forming alloys tended to undergo very little internal oxidation, except during exposures to conditions of low temperatures and low O2 concentrations. The dependencies of metal penetration and penetration rate upon exposure time showed that all the alloys tended to oxidize with a parabolic time dependence. However, some of the alloys required up to 1,150 hr to establish the parabolic time dependencies. The influence of P O2 upon metal penetration was complex. Some alloys showed increasing oxidation with increasing P O2, while other showed less oxidation with higher P O2’s.

Subject
Iron nickel chromium alloys, Metal surfaces, Commercial alloys, Corrosion scales, Oxide surfaces, Penetration, Internal surfaces, Metals, Internal corrosion, Aluminum alloys, Internal oxidation, Alloys, Oxidation
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2004
Association for Materials Protection and Performance (AMPP)
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