High-entropy FeCoNiMnCu alloy coating on ferritic stainless steel for solid oxide fuel cell interconnects

A high-entropy alloy coating of FeCoNiMnCu was prepared on SUS 430 steel via magnetron sputtering for solid oxide fuel cell (SOFC) interconnects application. The coated steels were subject to thermal exposure in air at 800 °C for up to 10 weeks. Phase constituents, microstructure and area specific resistance (ASR) of the coated steel before and after the oxidation testing were investigated. Results indicated the alloy coating was thermally converted into a high-entropy spinel coating of (Fe,Co,Ni,Mn,Cu) 3 O 4 after oxidation and a protective Cr 2 O 3 layer was formed at the steel/coating interface. The (Fe,Co,Ni,Mn,Cu) 3 O 4 spinel coating effectively suppressed growth of Cr 2 O 3 layer and outward diffusion of Cr during the long term exposure. Scale ASR of the coated steel was as low as 6.59 mΩ·cm 2 at 800 °C after 10 weeks. It indicates that (Fe,Co,Ni,Mn,Cu) 3 O 4 is a promising coating material for SOFC metallic interconnects. • A high-entropy alloy coating of FeCoNiMnCu is sputtered on SUS430 steel. • The coating is thermally converted into a high-entropy (Fe,Co,Ni,Mn,Cu) 3 O 4 spinel. • The spinel coating effectively suppresses growth of Cr 2 O 3 and out-diffusion of Cr. • Area specific resistance of coated steel is sufficiently low after long term exposure.