Brazing stainless for cryo temps?

I want to make small closed-type impellors for pumping cryogenic liquids
(LOX, perhaps later LH2) under high stress, low weight conditions. This is
for experimental purposes, at least at first. Suggestions for a production
version are also welcome.
It's part of my ongoing effort to make turbopumps for bipropellant
cryoliquid model rocket engines. :) I'll probably use mini-jet turbine
parts for the turbine wheels.
The impellor has complex interior surfaces, so I thought of making it up
from computer generated plasma/laser (?) cut ~1 mm layers of 304 (?)
stainless. I'd put removable tabs on the outside of each layer in order to
get the registration right, and bulk braze them together to form a whole.
Then heat-soak for a while, partly to distribute stresses and partly to
allow the braze and the base metal to mingle.
Any suggestions for a brazing material?
I'd then like to coat all the interior surfaces in a lower melting braze, in
order to smooth the interior surfaces - basically two-step brazing, except
the second stage is just a covering/smoothing layer.
Again I'm looking for suggestions for a brazing material. I thought of using
449 and 456 (449 and 456 are UK types), any comments? Any sources for 449 in
small quantities?
Any other suggestions or comments?
The finished impellors will have to pump LOX at cryogenic temperatures.
Reply to
Peter Fairbrother
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Contact Wall Colmonoy
They specialize in furnace brazing nickle alloys for aerospace parts.
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Reply to
Ernie Leimkuhler
Be sure the filler and metal is Cryo qualified. Some metals go nuts under cold conditions and others get stronger.
Reply to
Martin H. Eastburn
Speaking with absolutely no expertise, it seems to be a complex way of making the thing. I would have thought that the resulting composite structure would be sufficiently variable to make balancing an interesting problem, and who knows what will happen at cryogenic temperatures ? I would have thought that anything other than a homogenous piece was asking for trouble ...
I'd look at lost wax casting, or possibly machine from the solid with a CNC EDM (something I've always wondered about building !)
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Reply to
Dave Garnett

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