Effects of atmospheres on bonding characteristics of silver and alumina
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Joints prepared using a silver-copper oxide based reactive air brazing (RAB) technique is known to experience a significant decrease in joint strength when exposed in a reducing atmosphere at high temperature. To investigate the effects of atmospheres on the bonding characteristics of ceramic joints brazed with Ag-CuO braze filler metals, alumina joints prepared using a series of Ag-CuO compositions were exposed to a reducing atmosphere in hydrogen and also reoxidized in air at 800°C. All the brazed joints exposed to hydrogen revealed significant reduction in flexural strength and exhibited debonding of the interface between the braze filler and the alumina substrate. In the case of the joints brazed with a braze filler containing a high copper content of 8 mol%, the formation of interfacial porosity caused by the reduction of interfacial oxide phases led to an extremely weak interface, which was not recovered after subsequent reoxidation in air at 800°C. However, no significant microstructural change or interfacial porosity formation was observed in the braze filler metals containing no or low copper contents, and the interface remained intact even though interfacial strength was weak. Subsequent reoxidation of the joints with these filler materials resulted in the recovery of interfacial strength and flexural strength. This result clearly indicates that the bonding characteristics of the silver/alumina interface are by and large influenced by atmospheres of high temperature exposure. XPS analysis conducted on the in-situ¬ fractured surfaces of as-brazed and hydrogen-treated samples prepared using a braze filler with 2 mol% Cu indicated that oxygen in the silver matrix plays a critical role in bond strength between silver and alumina. The sample exposed in inert atmosphere also revealed low flexural strength and debonding of the silver/alumina interface, confirming the role of oxygen on the bond strength between silver and alumina.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 947906
- Report Number(s):
- PNNL-SA-55674; IJHEDX; 10001; AA2530000; TRN: US200905%%302
- Journal Information:
- International Journal of Hydrogen Energy, Vol. 33, Issue 14; ISSN 0360-3199
- Publisher:
- Elsevier
- Country of Publication:
- United States
- Language:
- English
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