Investigations of Mn–Co–O and Mn–Co–Y–O coatings deposited by the magnetron sputtering on ferritic stainless steels

Protective coatings for the metal interconnects of solid-oxide fuel cells have been produced by magnetron sputtering of metal targets sintered from mixtures of Co and Mn powders with a Y2O3 additive. Oxidizing heat-treatment of the metal coating in air at 800 °C and the reactive mode of coating deposition in which a cubic spinel structure formed immediately during coating deposition were used. The plasma providing for ion assistance was produced by ionizing the gas mixture in the working chamber with a low-energy broad electron beam. It has been demonstrated that the reactive mode promotes stabilization of the coating composition in the course of high-temperature testing. The effect of an yttrium additive (0.014–1.4 at.%) on the oxidation rate and area specific resistance (ASR) of the coated steel has been investigated. Thermogravimetric tests have shown that a 1.4 at.% Y additive to a spinel coating reduces the oxidation rate for AISI430 and Crofer 22 APU steels by a factor of 27.8 and 8.6, respectively. For the coated AISI430 steel, the ASR increased to 100 mΩ·cm2 within 1–2 thousands of hours, depending on the Y content in the coating. For the Crofer 22 APU steel with a Y-doped coating, the ASR decreased to a 6 mΩ·cm2 within several hundreds of hours and then increased to 15 mΩ·cm2 within 5000 h. For the MnCo2O4-coated Crofer 22 APU specimens, the ASR gradually decreased from 11 to 6 mΩ·cm2 within 5000 h.