Advanced Ceramics for
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Products : Ceramic to metal brazed assemblies

Various methods of assembly exist to bind ceramic to metal. When it comes to make an assembly that can resist to mechanical stresses and/or high temperatures, be vacuum leak tight and withstand corrosive environment, high temperature braze sealing is essential.

Applications

Ceramic-to-metal brazed assemblies are particularly suited for use in such severe environments as, for instance :

  • airborne electronics for the aerospace - civilian and military,
  • defense devices,
  • medical and analytical instruments,
  • high-energy physics, high and very high vacuum,
  • the nuclear industry.

Products

The product range given here below is for instance only, as we specialize in custom-made products :  

  • electrical feedthroughs for medical implants – cochlear and heart pace makers
  • hermetic packages for airborne electronics, analytical tools and devices for the oil industry,
  • high-voltage hermetic connectors for the nuclear industry,
  • high-voltage insulators for electron tubes.

Materials

Not all advanced ceramics can be brazed. There are mainly :

  • aluminium oxide (alumina, saphirre,rubi) and beryllium oxide,
  • and to a lower extent aluminium nitride, silicon nitride, silicon carbide, boron carbide, zirconia…

The metal associated with the ceramic must have a close CTE – coefficient of thermal expansion – in order to minimize residual stresses in the joint that would lead to rupture. The following metals are most commonly used :

  •  kovar, copper, titanium, nickel-iron, stainless steel, molybdenum, niobium, platinum…

The braze alloy to be used will depend upon various parameters : final temperature of use of the product, nature of the metal to be joined, several metals of different kinds to be brazed. The following alloys Ag-Cu, Ag-Cu-Pd, Ag-Cu-Au, Au-Cu, Au-Ni, Ag, Au, Cu are typical and cover a range of temperatures from 780°c to 1100°c.

A ceramic to metal assembly can be done in various ways, but all of them require that a metal interlayer be deposited so that the adhesion of the subsequent brazing will be possible :

  • sintered thick layer of molybdenum-manganese, only with oxide ceramics (alumina, beryllium oxide..)
  • thick layer of a reactive metal that chemically reacts
  • thin layer of W-Ti for instance deposited by PVD process.