The employment of ferritic-martensitic steels e.g., P91, as structural materials in concentrated solar power (CSP) plants can significantly increase cost-efficiency. However, their application is strongly restricted by their lower corrosion resistance in molten nitrates, compared to austenitic steels or Ni-based alloys. In this study, Cr-, Al-, and Cr/Al-diffusion coatings were deposited on P91 via pack cementation in order to improve its scaling behavior in molten solar salt (MSS). The corrosion behavior of coated specimens was investigated with respect to uncoated P91 in MSS at 600 °C for up to 1000 h. The exposure in MSS resulted in a thick, highly porous, and multi-layered oxide scale on uncoated P91 consisting of hematite, magnetite, and sodium ferrite. On the other hand, the scale grown on the chromized P91 comprised of a thin Cr-rich inner layer, which shifted breakaway to prolonged exposure durations. The aluminized specimens both formed very thin, highly protective alumina scales with localized protrusions.

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.

The influence of Pt- and Pt/Ir-modifications on the mechanical properties of NiAl coatings after thermocyclic exposure at 1100°C was investigated. Four-point-bending tests with in-situ acoustic emission measurement were used to determine the fracture strain. After 100 h of exposure a steep increase in fracture strain was observed for the NiAl coating. In contrast, the increase was found to be moderate for modified coatings. For all investigated coatings the fracture strain was correlated with the mean Al-concentration in the diffusion zone, and a moderate increase in the β-phase field with decreasing Al-concentration was found. In the two-phase (β/γ') stability region fracture strain increased steeply. Indentation hardness instead showed a steep decrease within the single β-phase field, but remained almost constant in the two-phase region. Reduced elastic modulus followed a V-curve behaviour, in which a decrease with ongoing Al-depletion in the β-stability region was followed by an increase in the two-phase region.