Mechanical characterization of oxide coating-interconnect interfaces for solid oxide fuel cells

This paper reports on the characterization of interfaces between oxide coatings and metallic interconnects that are used in planar solid oxide fuel cells. With the reduction of operating temperatures to 800 degrees C, it is possible to replace ceramic interconnects with less expensive stainless steels. However, when incorporating chromia-forming metallic interconnects, steps must be taken to inhibit chromium poisoning. One approach to prevent chromium poisoning, is to deposit dense, protective coatings, such as manganese cobalt spinel oxide (MCO). The brittle nature of MCO makes it susceptible to damage under mechanical and thermal stresses during operation. A four point bend experiment is designed to assess the strength and adhesion of reduced and oxidized coatings deposited on SS441 or Crofer interconnects. Resulting tensile cracking patterns on the convex side of bend specimen are used to quantify the interfacial shear strength with a shear lag model. Using energy based fracture mechanics, interfacial fracture energy is calculated from the strain at the onset of coating spallation. Scanning electron microscopy images of the cracked coating surfaces are processed to analyze the failure mechanisms, crack spacing and spalled areas. At 3% strain, the weakest interface is found in the Crofer system with the oxidized coating. (C) 2012 Elsevier B.V. All rights reserved.