Torsional behaviour of a glass-ceramic joined alumina coated Crofer 22 APU steel

Abstract

The robustness of the sealings used for the solid oxide cell (SOC) stack technology is crucial to prevent gases from mixing and failure. With a desire to increase the internal operating pressure the mechanical performance requirement of sealings increases. The mechanical behaviour of a glass-ceramic joined steel (Crofer 22 APU) and glass-ceramic interfaces used in SOC stacks has here been studied. The shear strength was measured at room temperature using a torsion test of as joined and aged (700 h in air at 750 °C) hourglass shaped samples. The Crofer 22 APU steel samples were coated with alumina before joining and the joining process was designed on the basis of shrinkage measurements taken from hot stage microscopy. The glass-ceramic joining material was applied as a tape casted foil between two alumina coated half hourglass steel samples, and then joined at 800 °C in air. Cross-sections and fracture surfaces were investigated, by means of SEM-EDS, to understand the effect of ageing on the joined samples. XRD was carried out on the as joined and on the aged glass-ceramic materials to investigate the ageing effect on the amorphous and crystalline phases. The shear strength of the as joined and aged samples was measured on six samples per group, and values of 40 ± 6 MPa and 34 ± 6 MPa were obtained, respectively.