Characterisation of Several Nickel-Base Alloys in Metal Dusting Environments

Metal dusting is defined as degradation of alloys at moderately high temperatures (400 deg to 800 deg C) in atmospheres of high carbon activity (ac > 1) and low oxygen partial pressure. The alloys disintegrate into a dust containing carbon filaments and particles of metal and oxide. The phenomenon has been observed in many industrial plants, such as the production of syngas from hydrogenation of carbon monoxide. The initial stages of metal dusting of several nickel-base alloys have been investigated and the results are reported here. The alloys (601, 603XL, 617, 671, 690 and 890) were exposed to a gas mixture of 80%CO / 20%H2, at 650 deg C, for periods of 100h. Before exposure, the specimens were ground to 600 grit finish. They were placed in ceramic crucible containers, and exposed to the gas mixture. Examination of the specimens revealed that they reacted differently, depending on their compositions and microstructures. Although formation of a protective and self-healing surface oxide layer should give reasonable protection to the alloys, localised failure, leading to significant damage, was generally observed. Analyses of the reaction zones that develop on the specimen surfaces have been carried out by EDX and EPMA. The results of this study are presented and discussed, with emphasis on the effects of the experimental set-up on the alloy performance. [This is an unrefereed preprint].