[AR] Re: 3D-printed RL-10
- From: Peter Fairbrother <zenadsl6186@xxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Fri, 7 Apr 2017 16:27:02 +0100
On 05/04/17 08:32, Uwe Klein wrote:
Am 05.04.2017 um 08:41 schrieb Dave Klingler:
... Using pre-consolidated powder as
SLM stock might actually cut the cost quite a bit, again, if that’s what
they’re doing, which might bring it down into amateur territory.
Dumb question: what do you describe as "pre-consolidated"
Uwe
My take:
Hard particles of about 1-2 micron size, spread evenly in a softer
matrix, can increase the creep resistance, yield and high temperature
strength of the matrix. In GrCop-84 the hard particles are crystals of
Cr2Nb, and the matrix is pure-ish copper.
[ A similar material of potential interest for rocket engine turbine
blades is thoriated/ceriated Inconel, in which particles of thorium
oxide (or more recently, cerium oxide) are dispersed in Inconel; this
can increase the usage temperature by 200 K or more. I digress ]
In order to make a part with evenly dispersed hard particles, you can
first make the material into a fine powder, consolidate the powder, then
use some semi-traditional engineering techniques, like rolling, forging,
friction stir welding, turning etc on the consolidate.
Unfortunately, anything which actually melts the material, eg welding,
casting, even some forms of heat treatment, causes the small particles
to either float or sink, and they are no longer evenly distributed.
In GrCop-84 (and many other consolidates) the particles also grow larger
when the matrix is melted.
If you want to 3D print a metal, you would in general use a powder in
the 10-50 micron range, though finer powders are used sometimes.
A non-consolidated powder might contain 2 micron Cr2Nb powder and 2
micron copper powder, just mixed together - if you can keep them
thoroughly mixed throughout the 3D printing process, then the final
print should have an even distribution of fine Cr2Nb particles.
However, I have doubts about the practicality of this, and suspect they
use pre-consolidated powders, ie powders in the ~ 20 micron grain size,
each grain of copper containing several hundred 2 micron Cr2Nb particles.
The very fast heating/cooling cycle would not allow for much separation
of Cr2Nb, and nature of the 3D printing process itself would prevent any
gross migration of Cr2Nb particles.
-- Peter Fairbrother
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