Metal dusting of Ni-Cu alloys: Dependence of high-temperature attack on crystal orientation and small amounts of thermodynamically stable oxide formers

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In order to further increase the efficiency of high-temperature processes, the conditions are becoming more and more aggressive, which places ever higher demands on the metallic structural materials such as Ni-based alloys. In the case of H 2 production high temperature processes high-temperature processes with reducing, carbon-rich atmospheres, as previously known from the chemical and petrochemical industry, are becoming increasingly relevant. In these processes, material degradation occurs due to the aggressive high-temperature corrosion form of metal dusting. In this project the attack mechanism of the metal dusting of Ni-Cu alloys and its kinetics are investigated with respect to the surface orientation, the alloy composition, and the variation of the process atmosphere. Alloying with Cu has been shown to reduce metal dusting attack, but the underlying mechanism and in particular its influencing factors are still unclear. To confirm, refute or extend existing theories, the influence of the Cu content and that of 2 wt.% Mn, Fe, Ti, Nb, Mo, Si or Cr and 4 wt.% Al, all of which form thermodynamically stable oxides, on the metal dusting resistance of the alloys is investigated. For this purpose, single-crystal model alloys with binary, ternary, and quaternary compositions are cast. Their resistance towards metal dusting is tested in two different atmospheres (with and without alcohols) and linked to the thermodynamic stability of the gas compositions. Thermogravimetric analysis also allows comparison between quaternary Al-containing alloys, which form protective oxide layers, and their ternary counterpart, which contains only Cu as the protective alloying element. These fundamental investigations are used for the targeted development of metal dusting-resistant materials for both established and new applications, e.g. with increased proportions of alcohols in the process gas.