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What is hot isostatic pressing (HIP)?

Hot isostatic pressing (HIP) is the simultaneous application of high temperature and pressure (in 3-dimensions) to produce a dense (or bonded) component. It finds use in processing both metals and ceramics. The component is surrounded by a gaseous medium (typically argon) and undergoes a thermal treatment at high pressure to consolidate the materials.

Because of the isostatic nature of the pressurising medium, greater flexibility with regard to sample shape is achieved through this process, and because of plastic deformation at the interface, surface preparation need not be so stringent.

It may be possible to alleviate some of the coefficient of thermal expansion mismatch problems associated with bonding dissimilar materials, since component design is more flexible. Therefore the design can be arranged such that a compressive stress is obtained at the interface on cooling.

This process also allows simultaneous densification and bonding of powders or porous bodies.

The critical aspect of this technique is that the interface must be isolated from the gaseous pressure medium. This is often achieved by encapsulating the component. There are three main types of encapsulation:

  1. direct sealing of the circumference of the contact area between the two parts;
  2. placement of a sleeve of material around the contact area between the two parts;
  3. full, or partial encapsulation of the entire component.

After HIPing, the encapsulant material is normally machined off.

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