Dilute additions of hafnium to silver make very useful active metal braze alloys. In this work, brazing of 94% alumina ceramic with Ag filler metal containing 2.5 or 3.4 wt.% Hf and a trace of Si was investigated. Heating was performed in a batch-type furnace under a dry positive hydrogen atmosphere. Test geometry included single-sided (sessile drop), two-sided (sandwiched braze joint), and tensile button specimens. The two-sided specimens were subjected to a partial vacuum purge at the brazing temperature to remove entrapped gas and porosity from the liquid braze before solidification. The Ag-3.4 Hf alloy yielded particularly good hermeticity and tensile button results, with failures in the bulk ceramic. The vacuum purge was effective in reducing joint porosity.
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