[TheForge] Re: Powder Damascus

[James Binnion]

>me> Here's an interesting bit for the Damascus/pattern-welding guys:
>me>
>me> Patterned steel billets by powder metallurgy.  [snip]
>
>AndyV> I'm not sure why this has been regarded by some with such
>AndyV> fascination.  It's nothing much more or less (depending on how
>AndyV> you look at it) from good old fashioned sintering.
>
>I dunno.  The sintered widgets I've seen appear to be to some degree
>porous.  The sintered particles aren't totally fused, just, well,
>stuck very firmly together.  In this powder Damascus technique, the
>sintered billet gets rolled and forged to completely fuse the granular
>sarting material.

The density of a sintered product among other things depends on the 
packing fraction (the density before firing) and the pressure applied 
during sintering as well as the time and sintering temperature. The 
sintered material you are referring to as porous would have large 
pores either because the powder was not of a shape and size 
distribution to pack densely, the pressure of the sintering process 
was not high enough to produce a fully dense product or the time or 
temperature was not sufficient to for fully dense sintering. Many 
sintered products approach the theoretical density of an alloy with 
densities of greater than 99.5% of the theoretical. Which is as good 
or better than any cast or forged product. The sintering process that 
Damasteel uses is HIP (Hot Isostatic Pressing). The powder is placed 
in a can that is welded shut and the can is placed in a furnace/ 
pressure tank and taken to high pressure (30-350 Mpa 4000-50,000 psi) 
using an inert gas and high temperature. This compacts the powder 
into a highly dense mass. A HIP billet will typically be in the 
greater than 99% dense class. The forging and rolling they do is 
mostly to give it a useable form and for pattern development.
-- 
Jim Binnion

James Binnion Metal Arts
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