Hot isostatic pressing

From Wikipedia, the free encyclopedia

Hot isostatic pressing (HIP) is a manufacturing process used to reduce the porosity of metals and influence the density of many ceramic materials. This improves the mechanical properties, workability and ceramic density.

The HIP process subjects a component to both elevated temperature and isostatic gas pressure in a high pressure containment vessel. 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 vessel to increase. Many systems use associated gas pumping to achieve necessary pressure level. 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 45,000 p.s.i. (310 MPa). 15,000 is the most common. Process soak temperatures range from 900°F (480°C) for aluminum castings to 3632°F (2,000°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. Primary applications are the reduction of microshrinkage, the consolidation of powder metals, ceramic composites and metal cladding. Hot isostatic pressing is also used as part of a sintering (powder metallurgy) process and for fabrication of Metal Matrix Composites.