Evolution of the interfacial phases in Al sub(2)O sub(3)-Kovar super( registered ) joints brazed using a Ag-Cu-Ti-based alloy

A systematic investigation of the brazing of Al sub(2)O sub(3) to Kovar super( registered ) (Fe-29Ni-17Co wt.%) using the active braze alloy (ABA) Ag-35.25Cu-1.75Ti wt.% has been undertaken to study the chemical reactions at the interfaces of the joints. The extent to which silica-based secondary ph...

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Bibliographic Details
Published in:Philosophical magazine (Abingdon, England) England), 2017-04, Vol.97 (10), p.718-742
Main Authors: Ali, Majed, Knowles, Kevin M, Mallinson, Phillip M, Fernie, John A
Format: Article
Language:English
Subjects:
ALUMINUM OXIDE
Brazing
Chemical reactions
COPPER SILVER ALLOYS
Evolution
Ferrous alloys
Formations
INTERFACES
JOINTS
Microstructure
MICROSTRUCTURES
Nickel base alloys
PHASES
Silver
SILVER ALLOYS (50 TO 99 AG)
Superalloys
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Summary:A systematic investigation of the brazing of Al sub(2)O sub(3) to Kovar super( registered ) (Fe-29Ni-17Co wt.%) using the active braze alloy (ABA) Ag-35.25Cu-1.75Ti wt.% has been undertaken to study the chemical reactions at the interfaces of the joints. The extent to which silica-based secondary phases in the Al sub(2)O sub(3) participate in the reactions at the ABA/Al sub(2)O sub(3) interface has been clarified. Another aspect of this work has been to determine the influence of various brazing parameters, such as the peak temperature, T sub()p and time at T sub()p tau , on the resultant microstructure. As a consequence, the microstructural evolution of the joints as a function of T sub()pand tau is discussed in some detail. The formation of a Fe sub(2)Ti layer on the Kovar super( registered ) and its growth, along with adjacent Ni sub(3)Ti particles in the ABA, dominate the microstructural developments at the ABA/Kovar super( registered ) interface. The presence of Kovar super( registered ) next to the ABA does not change the intrinsic chemical reactions occurring at the ABA/Al sub(2)O sub(3) interface. However, the extent of these reactions is limited if the purity of the Al sub(2)O sub(3) is high, and so it is necessary to have some silica-rich secondary phase in the Al sub(2)O sub(3) to facilitate the formation of a Ti sub(3)Cu sub(3)O layer on the Al sub(2)O sub(3). Breakdown of the Ti sub(3)Cu sub(3)O layer, together with fracture of the Fe sub(2)Ti layer and separation of this layer from the Kovar super( registered ), has been avoided by brazing at temperatures close to the liquidus temperature of the ABA for short periods of time, e.g., for T sub()pbetween 820 and 830 degree C and tau between 2 and 8 min.
ISSN:1478-6435
1478-6443
DOI:10.1080/14786435.2016.1275868