There are certainly titanium parts on many aircraft and some are
brazed assemblies. The SR 71 was a titanium airframe aircraft but
they were horridly expensive to make are no longer produced.I don’t
know if any of their wing structures were brazed but certainly other
parts of its structure were brazed. Titanium is so difficult to work
that its use is restricted to places where no other material will do
the job. That is why the vast majority of airplane wings are aluminum
or in the case of the newest ones graphite composites as these
materials are more than adequate to the task and they are riveted and
or glued together.
As for intermetallics titanium forms two intermetallic compounds with
silver TiAg And Ti2Ag and it forms even more with copper (seven)
which is the other main component to silver solders. These
intermetallics do occur in the brazed joints. That being said you
can indeed braze Ti with silver solder in a argon or vacuum furnace
just not with a torch. Regular silver solders are a problem though
because of brittle joints from the copper titanium intermetallics and
joint erosion again caused by the copper. Pure silver is acceptable
as a braze filler metal or a 95% silver 5% aluminum braze alloy.
There are a whole host of braze alloys for titanium if you are
brazing in argon or vacuum. Sure you can try to glop on some solder
and might get some kind of weak joint but it will not wet the
titanium. This is why titanium is often used for solder pics, it is
damn hard to get the solder to stick to it.
You need a highly reactive solder and flux to deal with torch
brazing of titanium because of Ti’s affinity for oxygen you need some
very reactive materials to strip the oxides from the joint. That is
why the braze alloys for Ti torch work are aluminum or magnesium
based and the fluxes contain fluoride chloride and lithium compounds.
I spent part of the afternoon making up some samples of attempts at
brazing titanium with a torch. None of them were successful I did
make a brazed joint with a TIG brazed silver solder puddle that I
then brazed a earpost on it and it cracked as soon as I tried to flex
it due to the intermetallic issue. I also did another example using
the PUK to weld a small dot of gold onto the titanium and then torch
brazed an earpost on it which was quite successful but it did
require the use of a PUK to make the gold pad to braze to.
I am writing a blog post with pictures of these experiments and it
will be done sometime tonight or tomorrow morning so if you would
like to see the results you can go to
tomorrow some time and look at it.
James Binnion Metal Arts