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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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