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Normally, the brazing of ceramics is a difficult matter since standard brazing alloys will not wet ceramic materials directly. Two brazing options exist for joining ceramics to metals or ceramic to ceramic.
One method involves coating the ceramic with molybdenum / Maganese or some other type of metallizing procedure. Once this is done, the coated ceramic can be brazed with standard filler metal. Unfortunately this metallizing process is very complicated and expensive to perform.
The second option involves a direct brazing process using on active metal. This process is suitably called "active metal brazing."
In active metal brazing, the filler metal used contains active metal additions that process, ceramics can be directly brazed.
Active metal products will join many types of ceramics and other hard to wet materials like carbide, diamond, sapphire, alumina, zirconia, silicon nitride, silicon beryllium. These materials may be joined to themselves or to common substances such as stainless steel, copper, tool steel, kovar, etc.
In the direct brazing process, the brazing should be done in a vacuum, 1 x 10-4 Torr minimum, or in an inert gas atmosphere using argon or helium.
Active metal brazing uses the following alloys: Braze 720, Braze 715, Permabraze 616 and Braze 559. These active metal products are available from active metal products are available from Lucas - Milhaupt in two forms; a paste material named Lucanex® and a strip product called Cerametil.
In the paste form, Lucanex® can be dispensed or silk screened on the parts to be brazed. This offers the advantage of conformance to any configuration. Wrought form products or Cerametil must be processed to the correct size.
Flux is critical to the brazing and soldering process because it minimizes the oxidation that may form on both the brazing filler metal and the materials being joined. The majority of common brazing applications are readily met by Handy Flux, the general purpose fluz that has remained an industry standard for over 50 Years.
For low temperature brazing, Sure Flo Flux is a creamy and smooth composition that provides excellent adhesion to parts. Its consistent blend will not spatter or run during a rapid heating cycle. Sure Flo offers excellent fluxing action and oxide removal and will not crystallixe under normal conditions.
We also offer fluxes for virtually every specealized application including formulations for high and low temperature applications, furnace and induction brazing, as well as those for automatic flux dispersers.
For more information on any of these fluxes, or a recommendation on which flux to use, contact Techical Services Department.
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