| dc.description.abstract | The aim of this study was to investigate the thermal cycling-creep properties and fracture pattern of the joint between metallic interconnect and braze sealant in metal-supported solid oxide fuel cell system. The materials used were a Ag-Ge sealant developed at the Institute of Nuclear Energy Research and a commercial Crofer 22 H ferritic steel. The thermal cycling-creep test was conducted by applying a constant load (shear or tensile mode) on the joint under thermal cycling between room temperature and 750 °C in air. Effects of thermal aging were also considered. Fracture surfaces were analyzed using scanning electron microscopy to investigate the fracture patterns.
Experimental results showed that the number of cycles to rupture of both unaged and aged joints was increased with a decrease in the applied constant shear and tensile loading at 750 °C. The tensile and shear strength of unaged joint at 100 thermal cycles, equivalent to accumulated time of 1000 h at 750 °C, was 4.98 MPa and 3.54 MPa, respectively. In comparison with creep strength of unaged joint at 1000 h, it was reduced by 9.1% and 0.6%, respectively. The tensile and shear strength of aged joint at 100 thermal cycles was 3.86 MPa and 3.11 MPa, respectively. In comparison with creep strength of aged joint at 1000 h, it was reduced by 19.6% and 14.6%, respectively. Apparently, the combination of thermal cycling and creep would generate more damage than pure creep, leading to a shorter rupture time.
For unaged tensile and shear joints, fracture mainly occurred at the interface between Cr2O3 and braze with a short thermal cycling life. For a longer accumulated time at high temperature, more and more AgCrO2 formed at the joints with a medium or long thermal cycling life. Fracture sites gradually transformed to the interface between AgCrO2 and braze. For aged tensile and shear joints, fracture mainly occurred at the interface between AgCrO2 and braze. In addition, the longer thermal cycling life the aged joints sustained, the more remarkable this phenomenon was. On the other hand, for the aged joints with a shorter thermal cycling life, more fracture occurred at the interface between Cr2O3 and AgCrO2. | en_US |