Metal dusting attack is a serious problem in processing industries using carbonaceous gases and high temperatures. Ni-based alloy 699 XA was recently developed as an alloy for these types of environments with high resistance against metal dusting. In this study, different surface treatments of this chromium-and aluminum-rich alloy are shown to have an important influence on the metal dusting onset behavior. It was found that surface treatments that are traditionally considered to be helpful for fatigue performance, for example, shot peening, and pickling were detrimental to the metal dusting performance of alloy 699 XA.Additionally, the shot peening surface treatment promoted Fe surface contamination, resulting in a negative impact on the metal dusting pitting resistance of the alloy. Deformation accompanied by apparent BCC α-Cr precipitation in the bulk microstructure, but a comparison with cold-rolled materials shows that the surface treatment dominates the metal dusting resistance.

Corrosion by metal dusting causes problems in various industries that process carbonaceous gases. Recently, the chromium‐ and aluminum‐rich Ni‐based Alloy 699 XA was introduced as a material with high resistance against metal dusting attacks. In this study, the metal dusting degradation of Alloy 699 XA and model alloys was investigated. In the model alloys, the aluminum, chromium, and iron contents were varied to analyze the role of each element systematically. Alloy 602 CA was included as a reference material. It was found that the alloys with the highest chromium and aluminum contents (30 and 2–3 wt%, respectively) showed the highest resistance against metal dusting. Also, the limited addition of iron enhanced the aluminum activity and thereby promoted the formation and maintenance of an aluminum‐rich oxide scale. This effect at low iron levels is contrary to the negative impact of iron at higher levels, which typically leads to an increased metal dusting susceptibility. Exposure tests were performed with two gas mixtures having similar compositions, but different carbon activities. It was found that both gases had a similar aggressiveness regarding metal dusting attacks.

Oxidation of the Fe-base alloy T22 in humid air at 500 °C was investigated. The samples were exposed for up to 1000 h at 1 bar and 20 bar. The influence of three furnace tube materials, alumina, ET45 and quartz glass, on the oxide scale morphology was investigated. Samples and their cross sections were examined using optical microscopy, scanning electron microscopy, electron probe micro analysis and Raman spectroscopy. Multilayered oxide scales consisting of hematite, magnetite and Fe–Cr spinel were found on all samples. However, the composition and morphology of the oxide scales depend on the furnace tube material and on the system pressure. The system pressure is assumed to change the reaction equilibria and adsorption rates. The tube material changed the initial gas composition by formation of volatile Cr species. This volatilization rate increased at higher system pressures.

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Due to the inhibiting behavior of Cu, NiCu alloys represent an interesting candidate in carburizing atmospheres. However, manufacturing by conventional casting is limited. It is important to know whether the corrosion behavior of conventionally and additively manufactured parts differ. Samples of binary NiCu alloys and Monel Alloy 400 were generated by laser powder bed fusion (LPBF) and exposed to a carburizing atmosphere (20 vol% CO–20% H2–1% H2O–8% CO2–51% Ar) at 620 °C and 18 bar for 960 h. Powders and printed samples were investigated using several analytic techniques such as EPMA, SEM, and roughness measurement. Grinding of the material after building (P1200 grit surface finish) generally reduced the metal dusting attack. Comparing the different compositions, a much lower attack was found in the case of the binary model alloys, whereas the technical Monel Alloy 400 showed a four orders of magnitude higher mass loss during exposure despite its Cu content of more than 30 wt%.

Metal dusting is still an unresolved issue at high temperatures. Currently, two material-related strategies to mitigate metal dusting are described in the literature.On the one hand, highly alloyed materials are used, which contain large amounts of protective oxide-forming elements, such as Cr, Al, and Si. The second mitigation strategy is based on inhibiting the catalytic effect of Fe, Ni, and Co.These elements all strongly catalyze the formation of solid carbon from the gas phase. Combining the catalytic protection of Cu alloying for metal dusting with protection by a classical alumina/chromia barrier is a native feature that high-entropy alloys (HEAs) can offer. In this study, the behavior of different equiatomic HEAs with and without Al and/or Cu are studied when exposed at 620°C in a highly aggressive metal-dusting environment.

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