Electroless Ni-P coatings on low-Cr steels: A cost-efficient solution for solar thermal applications

A. Solimani, T.M. Meißner, C. Oskay, M.C. Galetz

Solar Energy Materials and Solar Cells 231 (2021), 111312, DOI: 10.1016/j.solmat.2021.111312

solimani2021_fig2

Left: Weight change behavior of blank and Ni–P-coated X20CrMoV12-1 steel as well as alloy 230 after immersion test in molten solar salt at 600 °C. Note the significant reduction of weight change kinetics by applying electroless Ni–P coating on X20 steel. Right: Macroscopic surface view of the samples after 100 and 1000 h immersion times.
Reprinted from Solar Energy Materials and Solar Cells, Copyright (2021), with permission from Elsevier.

solimani2021_fig9

BSE micrograph, element distribution maps, and the quantitative concentration profile of the scale and subscale zones for Ni–P coated X20CrMoV12-1 sample after 1000 h isothermal immersion in molten solar salt at 600 °C. The dotted line shows the position of line scan.
Reprinted from Solar Energy Materials and Solar Cells, Copyright (2021), with permission from Elsevier.

The corrosion behavior of an electroless Ni–P coating on low-Cr X20CrMoV12-1 steel as a cost-efficient substrate-coating combination is investigated in molten NaNO3–KNO3 nitrates at 600 °C. Results indicated that the as-deposited Ni–P coating was transformed to a thermally treated diffusion coating upon exposure to the molten salt without additional heat treatment prior to the exposure. Detailed evolution of the Ni–P coating and the oxidation behavior during the 1000-h immersion test is discussed. Results showed competitive corrosion resistance of the coating system compared to that of the sophisticated Ni alloy 230, with the advantage of an inherent barrier against Cr dissolution form the substrate. The significant corrosion resistance of the electroless plated Ni–P coating is attributed in part to the protective Ni--rich oxide scale and in other part to the in-situ formed Ni3P barrier at the oxide-substrate interphase boundary.

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