Hot isostatic pressing
Hot isostatic pressing (HIP) is a manufacturing process, used to reduce the porosity of metals and increase the density of many materials including nickel, cobalt, tungsten, titanium, molybdenum, aluminium, copper and iron based alloys; oxide and nitride ceramics; glasses; intermetallics; and premium plastics. This improves the material's mechanical properties and workability.
History
The main principal of hot isostatic pressing had been theorised in 1656 by Blaise Pascal and it is Pascal's Law that makes hot isostatic pressing work. Although isostatic pressing patents had been granted since the turn of the 20th Century (1913) the first being to Harry D. Madden who described an isostatic pressing technique in a US patent assigned to the Westinghouse Lamp Company, USA. It wasn't until 1956 that the first specific hot isostatic pressing was granted to Battelle’s Columbus Laboratories in the United States. The patent covered the isostatic-diffusion of gas pressure bonding application of HIP.[1]
Process
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 the necessary pressure level. Pressure is applied to the material from all directions (hence the term "isostatic").
For processing castings, metal powders can also be turned to compact solids by this method, the inert gas is applied between 7,350 psi (50.7 MPa) and 45,000 psi (310 MPa), with 15,000 psi (100 MPa) being most common. Process soak temperatures range from 900 °F (482 °C) for aluminium castings to 2,400 °F (1,320 °C) for nickel-based 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; this process improves fatigue resistance of the component. 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.[2]
References
- ↑ "The Interactive history of metallurgy". Bodycote. February 12, 2016.
- ↑ Atkinson, Dr H. V.; Davies, S. (2000-12-01). "Fundamental aspects of hot isostatic pressing: An overview". Metallurgical and Materials Transactions A 31 (12): 2981–3000. doi:10.1007/s11661-000-0078-2. ISSN 1073-5623.