Applying pressure while article cools

Claim 1

In a process for consolidating powder metals comprising the steps for (a) placing unconsolidated powder nickel-titanium alloy comprising from 53 to 62 weight percent of nickel the remainder of the alloy being essentially titanium in a sealable glass mold which becomes plastic upon heating, (b) evacuating the atmosphere from the powder filled mold, (c) sealing the mold, (d) placing the mold in a open top refractory container and packing with free flowing refractory powder selected to freely flow at all the temperatures used in the process, (e) heating the mold and contents of the mold to a temperature at which sintering of the powder metal takes place and holding at this temperature for a time sufficient to cause substantially complete densification of the powder nickel-titanium alloy, (f) cooling and removing the mold to recover a dense article, and whereby the glass mold is supported by the free flowing refractory powder as the mold becomes plastic and shrinks in volume as its contents densify, the improvement comprising: after step (e), transferring the open top refractory container, refractory powder, glass mold, and nickel-titanium object directly into an insulated, refractory lined covered container and then placing the covered container into a pressure chamber and applying an isostatic pressure of 2,000 psi or more to the nickel-titanium alloy object while it slowly cools down.