Ag–Al based air braze for high temperature electrochemical devices

Silver–aluminum based air brazing was attempted using an in situ alloying and brazing process. In this process, layers of foils of aluminum and silver were laid up between alumina plates in alternating fashion to achieve three target compositions representing Ag, Ag 3Al, and Ag 2Al phases. Each allo...

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Bibliographic Details
Published in:International journal of hydrogen energy 2007-11, Vol.32 (16), p.3754-3762
Main Authors: Kim, Jin Yong, Hardy, John S., Weil, K. Scott
Format: Article
Language:English
Subjects:
Ag–Al braze
ALUMINIUM ALLOYS
ALUMINIUM OXIDES
Applied sciences
braze
BRAZING
CRACK PROPAGATION
Energy
Energy. Thermal use of fuels
Equipments for energy generation and conversion: thermal, electrical, mechanical energy, etc
Exact sciences and technology
FILLER METALS
FRACTURE MECHANICS
Fuel cells
MATERIALS SCIENCE
MECHANICAL PROPERTIES
MICROSTRUCTURE
PHASE TRANSFORMATIONS
SILVER ALLOYS
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Summary:Silver–aluminum based air brazing was attempted using an in situ alloying and brazing process. In this process, layers of foils of aluminum and silver were laid up between alumina plates in alternating fashion to achieve three target compositions representing Ag, Ag 3Al, and Ag 2Al phases. Each alloy composition revealed different microstructure, mechanical properties and fracture mechanisms. Joints brazed with foils containing 9.8 at% Al formed a long continuous layer parallel to the direction of the original aluminum foil. The fracture occurred at low bend strength (6–12 MPa) mainly through the interface between this newly formed long alumina layer and the braze filler. Joints containing 26.5 at% Al in the braze filler metal experienced the series of phase transformations, leading to cracks in as-brazed specimens. The fracture initiated through these pre-existing cracks, thus the joint strength observed in these specimens was extremely low. The joints prepared using foils with 35.1 at% Al exhibited a good interface even though interfacial alumina particles formed during air brazing. Crack propagation occurred along the interface between the alumina substrate and in situ formed interfacial alumina particles or directly through these particles. Due to the good interface, the best bend strength (46–52 MPa) was achieved for the braze filler containing 35 at% Al.
ISSN:0360-3199
1879-3487
DOI:10.1016/j.ijhydene.2006.08.055