Hot isostatic pressing
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Hot isostatic pressing (HIP) is a manufacturing process used to reduce the porosity of metals. This improves the mechanical properties and increases workability.
The HIP process subjects a component to both elevated temperature and isostatic gas pressure in an autoclave. The pressurizing gas most widely used is argon. An inert gas is used, so that the material does not chemically react. The chamber is heated, causing the pressure inside the chamber to increase. Due to the presence of the gas, pressure is applied to the material from all directions (hence the term "isostatic").
For processing castings, the argon is applied between 15,000 p.s.i. (103 MPa) and 30,000 p.s.i. (206 MPa). 15,000 is the most common. Process soak temperatures range from 900°F (480°C) for aluminum castings to 2,600°F (1,315°C) for nickel base superalloys. When castings are treated with HIP, the simultaneous application of heat and pressure eliminates internal voids and microporosity through a combination of plastic deformation, creep, and diffusion bonding.
Hot isostatic pressing is also used as part of a sintering process and for fabrication of Metal Matrix Composites.
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