Residual stresses in suspension plasma sprayed electrolytes in metal-supported solid oxide fuel cell half cells

Abstract

Solid oxide fuel cells (SOFCs) efficiently convert chemical energy into electrical energy with fuel flexibility and low emissions. Plasma spraying has emerged as a fabrication technique for metal-supported SOFCs. Residual stresses in suspension plasma sprayed (SPS) yttria-stabilized zirconia (YSZ) electrolytes fabricated with various processing parameters and substrates were analyzed by X-ray diffraction. The temperature dependence of the residual stresses was also evaluated. The electrolyte residual stresses varied with both processing conditions and substrate characteristics, and ranged from 35 to 91 MPa. The change in stresses agreed well with the observed microstructural changes arising from the use of different processing conditions and substrates. The electrolytes fabricated using torch power and stand-off distance of 133 kW and 90 mm exhibited the highest residual stress due to the their relatively dense microstructure with low level of vertical cracking compared to electrolytes made with the other spray conditions. As these electrolytes were heated from room temperature to 750 °C, residual stresses decreased from 91 to 39 MPa. The decrease is due to changes in Young’s modulus and to thermal expansion mismatch between the layers, and possibly also due to the formation of additional microcracks or creep of the porous stainless steel substrate.