Hey Paul,

I heard about a material called Titanium Aluminide.  It can be forged
and machined.  It's light and can withstand high temperatures.  Maybe it
would be a good material to make some 20K RPM rotors from?

http://www.moelleraircraft.com/ti-al1.htm
http://en.wikipedia.org/wiki/Titanium_aluminide
http://www.precast.com/

Mark LaPierre

It is higher density than aluminum at .144 pounds per cubic inch.
Aluminum is .1 pound per cubic inch. Iron is .3 pounds per cubic inch.
The really trick alloy for rotors is beryllium aluminum at .07
pounds per cubic inch. Half the weight of Titanium Aluminide.

Paul Lamar