Influence of Preoxidation on High Temperature Behavior of W/Ni-Coated SOFC Interconnect Steel

Steel substrates were first preoxidized in air at 800 °C for 100 h. W/Ni coatings were then deposited by magnetron sputtering on both bare and preoxidized steel, followed by oxidation at 800 °C for 10 weeks. Both samples thermally converted to form a double-layer oxide scale composed of an inner Cr-rich oxide layer and an outer NiWO₄ layer. In the coated bare steel, continuous outward diffusion of Cr and Fe caused interfacial degradation and increased contact resistance. For the coated preoxidized steel, however, the preformed Cr-rich oxide layer significantly suppresses elemental interdiffusion and preserves interfacial integrity, and remains largely stable and continuous throughout the exposure. After 10 weeks, the area-specific resistance (ASR) of the preoxidized steel was 23.88 mΩ·cm², demonstrating good electrical conductivity. Substrate preoxidation offers a viable route for improving the long-term performance of W/Ni-coated interconnects.