If you can, give me some idea of the size of the tubes you are trying to join, can you live with a sleeve over the joint? johnscrowe@worldnet.att.net

The tubes are .056" OD x .032" ID. Sleeving the parts is highly undesireable.
The design uses a butt joint (not the strongest design).

earld

1)  What is your present method of limited success?
2)  Suggest furnace brazing in combination with diffusion bonding.  Consult a braze alloy supplier or furnace brazing source for proper selection of braze alloy.  support a ceramic rod from a drilled hole in a base plate and slide your tubes over the rod with braze alloy foil sandwiched between.  put a weight on the top tube.  The braze alloy will initiate bonding and the added weight will provide pressure for parent metal diffusion to occur.

good luck

Jesus is the WAY

The method with the most success has been brazing in dry hydrogen using AuGe (88/12). Braze alloy wetting to the sapphire is good, but marginal to the AlBeMet which has been coated on the braze surfaces with Au.

It appears as if the failure occurs because of intermittent wetting to the AlBeMet.
The alumina has been metallized with MoMg/Ni which is standard in the brazing industry. This surface wets well. The AlBeMet composition is 38Al-62Be.

earld

First time reading you post, I missed the Alumina.  Even though you are getting good weting on the Alumina, what about the strength of the bond.  In other words, where is the failure actually occurring?  Is the weak joint directly related to the wetting and therefore at the metal interface rather than the ceramic interface. I am a bit surprized because the wetting is opposite of what I would expect.

If the weak link is actually at the ceramic, there are several processes for metallizing the Alumina prior to brazing which provide excellent bonding to the ceramic.

What is the composition of the AlBeMet?

Leonard

Jesus is The TRUTH

erald

I received an error message that my reply to your post did not take but obviosly it did take.  Therefore duplicate copies.

Now I understand why you are getting such good wetting on the 'metallized' Alumina.  Have you considered NiAu 82/18 braze alloy?  Is the Au coating electroplated on the AlBeMet?  This certainly has to be the weak link (Au-AlBe) so I would be looking at another base metal and or process for coating the AlBe.

When you say intermittant is that on a macro or micro level?
If the AlBeMet is not proprietary, let us know the composition and surely someone will have an idea if is wettable by something.

Jesus is The TRUTH