Introduction

PNEUMATIC ISOSTATIC FORGING (PIF) is a technology for consolidating powder metal, or metal powder preforms to near or full density. The PIF process is a low-cost patent-pending technique for achieving high density and high performance in a range of materials. The short-time thermal exposure and lower processing temperature requirements relative to conventional processes provide a control of microstructure and related mechanical and magnetic properties.

The PIF process is a true forging process in which material is plastically deformed to achieve high density. The use of the term pneumatic is derived from the fact that argon or nitrogen gas is used as the pressure medium and is dispatched at pressures up to 415 MPa (60,000 psi), where the gas has fluid characteristics. The consolidation of the material is achieved by forging a workpiece with a gas hammer to high density. The workpiece is pressurized isostatically at a prescribed temperature in a uniform and rapid manner with a cycle time of 2 to 5 min. As such, PIF is a relatively highstrain-rate process that plastically deforms the workpiece. Selection of process parameters such as pressure, strain rate, temperature, and time at pressure is material dependent.

Pneumatic isostatic forging (PIF) and hot isostatic pressing (HIP) are similar to the extent that a gas-pressing medium applies isostatic pressure to the workpiece. Densification in HIP is achieved primarily through creep and diffusion with very limited use of plastic deformation. The PIF process uses plastic deformation and limited diffusion to achieve its goal. Furthermore, the strain rate for HIP is low and for PIF it is high.

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