HOT ISOSTATIC PRESSING

'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 process and for fabrication of Metal Matrix Composites.
In 1976, after an extensive development program, Howmet Corporation of Whitehall, MI (now Alcoa Howmet) became the first company in the world to offer HIP production services to the aerospace industry. A rapid rise in the use of HIP in gas turbine manufacturing followed as increasingly complex airfoils were required to meet increasingly stringent standards. By developing HIP, Howmet provided the means to produce the desired high density, fine grain material. Howmet's HIP facility in Whitehall, MI is today still one of the largest, most advanced HIP facilities in the world.