The effect of strain induced phase transformation on the thermal expansion compatibility of plasma sprayed spinel coating on SOFC metallic interconnect – A study using in-situ high temperature X-ray diffraction

Abstract

A new and novel approach has been adopted in this study to evaluate thermal mismatch induced by thermal expansion in substrate-coating contact pairs using in-situ high-temperature X-ray diffraction (HT-XRD). Atmospheric plasma sprayed (APS) Mn1.0Co1.9Fe0.1O4(MCF) coating on Crofer 22 APU steel interconnect was investigated. In-situ HT-XRD was performed individually for substrate and coating from 25 °C to 900 °C. Diffraction data were recorded for different temperatures to obtain lattice parameters and strain as a function of temperature. The coefficient of thermal expansion (CTE) of MCF coating was slightly higher than steel substrate and showed no significant thermal expansion mismatch till 700 °C. The increasing lattice strain measured by Scherrer and Williamson-Hall methods indicates strain-induced phase transformation of MCF coating with temperature, supporting the phase transformation-induced self-healing phenomenon of MCF coating. The merit of in-situ HT-XRD as a tool for optimizing operating temperature and measuring thermal mismatch of solid oxide fuel cell (SOFC) stacks has been discussed.