| dc.description.abstract | The objective of this study is to investigate the joint strength between a glass-ceramic sealant and metallic interconnect. The applied materials were the GC-9 glass ceramic developed at the Institute of Nuclear Energy Research (INER) and the commercial Crofer 22 H and APU ferritic stainless steels. A methodology of evaluating the joint strength at room temperature (RT) and 800 oC was developed by testing two types of sandwich-like specimens under shear and tensile loading.
The effects of joining temperature, pre-oxidization of metallic interconnect, number of initial spreading side, aging treatment, and composition of metallic interconnect on the joint strength at RT and 800 oC were studied. The measured shear strength of the specimens joined at 900 oC was greater than that of those joined at 850 oC. Apparently, an increase of joining temperature could improve the joining performance due to a better wetting behavior of glass ceramic. A pre-oxidization treatment at 900 oC for 2 h did not generate a beneficial effect on the shear and tensile joint strength for all the given testing conditions. The joint strength of specimens with a double-layer of glass-ceramic sealant was greater than that of single-layer ones due to a better wetting behavior of the GC-9 glass-ceramic sealant in contact with the metal slice during joining. Compared to the shear strength at 800 oC for the unaged joint specimens, a 17-19% reduction of joint strength was observed for the aged ones with various aging times. In comparison of the shear joint strength between Crofer 22 H and APU specimens, it is found that an addition of Nb and W elements in the Crofer 22 H steel provides a greater bonding strength with the GC-9 glass-ceramic sealant.
Through the analysis of interfacial microstructure, fracture modes of the joint were correlated with the measured strength. Three types of fracture modes were identified for the shear joint specimens. Firstly, the lowest joint strength was accompanied by delamination at the interface between the glass-ceramic substrate and an adjacent oxide layer, chromate (BaCrO4). Secondly, fracture at the interface between the GC-9 glass-ceramic sealant and the chromate layer as well as in the GC-9 layer accompanied a medium joint strength. Thirdly, a high level of joint strength was accompanied by delamination at the interface between the metal substrate and the Cr2O3 layer as well as at the interface between the GC-9 substrate and BaCrO4 layer. For the tensile joint specimens, a greater joint strength accompanied fracture in the glass-ceramic layer. However, delamination at the interface between the GC-9 substrate and BaCrO4 layer was also involved in the fracture in addition to the fracture of the glass-ceramic layer, for a lower level of tensile joint strength.
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