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3.  Hot Isostatic Pressing

Flexible, as opposed to fixed, dies are used in hot isostatic pressing (HIP) with the die and powder subjected to equal pressure in all directions (Figure 11).  In practice, a gas-tight container is filled with loose powder, heated, and degassed to remove any volatile contaminants.  After degassing, the container is sealed.  The compaction of the container occurs in an internally heated, cold walled pressure vessel.  High pressure gas is used to transfer the heat and apply pressure to the compact.  Temperatures of up to 2200°C and pressures up to 200 MPa are possible using the HIP process.  After pressurization, the compact is removed from the vessel and extracted from the container.  This method is used for the consolidation of materials such as tool steels, nickel base superalloys, titanium, and aluminum matrix composites.  The process results in full density and isotropic properties, especially in large parts.

Figure 11: Hot Isostatic Pressing Sequence-Schematic: Source "Powder Metallurgy Science" Second Edition, R.M. German, MPIF.

Representative parts fabricated by the several PM processes described are illustrated in Figure 12.

Figure 12: Representative PM Parts: Source "Powder Metallurgy Design Solutions,1999, MPIF.