Effects of oxide thickness on scale and interface stresses under isothermal cooling and micro-indentation for ferritic stainless steel interconnect

Interconnects in solid oxide fuel cells (SOFCs) provide the electrical connection between the individual cells, as well as separate the anode fuel from the cathode air for each cell. In this paper, we study the thermal stresses in the oxide scale and at the oxide/substrate interface for Cr-Fe based interconnect (IC), e.g. Crofer 22 APU, during cooling. The ultimate goal is to predict the interconnect life under typical operating conditions and thermal cycles. In general, very high compressive in-plane stresses are predicted in the oxide layer during cooling. High shear stress is also predicted on the oxide scale/substrate interface. The predicted shear stress on the interface will be used to compare with the experimentally determined bond strength to predict delamination. Finite element analyses are also performed for indentation test: high shear stress is predicted on the oxide/substrate interface, and the interfacial crack growth is predicted to be mode 11 driven.