Evaluation of Co and perovskite Cr-blocking thin films on SOFC interconnects

The viability of perovskite (LSC, LSCF, LNF and BSCF) and metallic (Co) thin film coatings to reduce Cr migration from Crofer22, E-Brite and SS430 interconnect materials has been examined. Production-scale physical vapor deposition (PVD) systems were used to obtain uniform films with thickness near 1 μm. The LSC, LSCF, LNF and Co films exhibited good adhesion, thermal stability and chemistry similar to the target materials. Although the BSCF films exhibited good initial adhesion, subsequent reactions caused blister formation upon thermal cycling. Chromium migration upon extended thermal treatments of 168 h was investigated using XPS depth profiling through the films. As a result of interdiffusion of elements across the film-substrate interface, intermediate spinel layers were formed spontaneously in all thin films, with concurrent shifts in compositions of the perovskite films. With the exception of the BSCF films, the combination of a perovskite or Co coating and the spontaneously-formed, chemically graded intermediate spinel layers was highly effective in blocking Cr diffusion from the interconnect materials.