Characterization of a metallic interconnect operated in stack during 40,000 hours in SOFC mode

An SOFC stack operated for 40,000 hours has been dismantled offering the opportunity to characterize the metallic interconnect. The metal plate was carefully investigated to define the evolution of the surfaces exposed to the air and to the hydrogen electrodes respectively. The observations of the surfaces reveal the stability of the layers applied on top of the rib at the air side while in the bottom of the channels the protective coating (i.e., Co-Mn base spinel oxide) shows large crystals. The cross section allowed to highlight the formation of a rather homogeneous layer of thermal grown oxide between the metal and the coating. The average thickness of the TGO is around 11 μm. The hydrogen side shows a superficial alteration (due to the interaction with the water vapour) changing from the inlet to the outlet where it seems thinner as if the TGO further reacted by forming volatile compounds. The cross section observations confirmed the presence of a porous TGO with a rather high content of manganese in a Cr-Mn spinel oxide. Several spots testifies the zones of contact with the Ni base contacting layer. The cross section corresponding to such zones highlighted the Ni diffusion in the metal substrate.

Residual Stress in Oxide on NiCrAlY Coating Evaluated by Photoluminescence Spectroscope

The purpose of this study was to understand the effects of thermal exposure temperature on residual stress in thermal grown oxide (TGO) on NiCrAlY coating. The residual stresses in the TGO layer were measured by photo-stimulated luminescence spectrum. High velocity oxygen fuel sprayed (HVOF) method was used to fabricate NiCrAlY coating material. The thermal exposure tests were conducted in air at 900°C, 1000°C, 1100°C for up to 1000 hours using an electric furnace. It was shown that the thickness of the TGO increases with an increase in thermal exposure time with a parabolic curve. The residual stress in the TGO layer increases in thermal exposure time up to 75 hours, and then, the residual stress in the TGO layer decreases slowly. The effects of surface roughness on the residual stress in the TGO were discussed based on experimental results and analysis.

Shakedown on Thermal Barrier Coating and Simply Analytic Model

A simply analytic model is developed base on wrinkle geometry model. The three concentric circles are adopted to represent top coat, oxide coat and bond coat of thermal barrier coating, and then shakedown analysis is established based on the model. A numerical model has been given base on wrinkle geometry model in a thermal barrier coating system, and the model on static shakedown analysis is developed by finite element method. Shakedown limit of thermal barrier coating is calculated for various undulation shape and thermal grown oxide. The simply analytic results and numerical results are approximate for undulation shape is not very irregular. The simply analytic model is convenient for calculating shakedown limit of thermal barrier coating.