Editing Hot isostatic pressing

{{Short description|Manufacturing process}}
{{Refimprove|date=January 2017}}
[[File:ISOSTATICALLY PRESSED NICKEL ALLOY TEST SPECIMENS - NARA - 17441738.jpg|thumb|Isostatically pressed{{Clarification needed|reason=Through hot isostatic pressing?|date=December 2024}} nickel alloys]]
'''Hot isostatic pressing''' ('''HIP''') is a [[manufacturing]] process, used to reduce the [[gas porosity (casting)|porosity]] of [[metal]]s and increase the [[density]] of many [[ceramic]] materials. This improves the material's mechanical properties and workability. 

The HIP process subjects a component to both elevated temperature and isostatic gas pressure within a high-pressure containment vessel, unlike the cold isostatic pressing (CIP), where the component is maintained at room temperature.<ref>{{cite web |url=https://www.sputtertargets.net/blog/an-introduction-to-cold-isostatic-pressing-cip.html |title=An Introduction to Cold Isostatic Pressing (CIP) |date=Sep 21, 2023 |last=Green |first=Julissa |website=Sputter Targets |access-date=Oct 7, 2024}}</ref> The pressurizing gas most widely used is [[argon]]. An [[inert gas]] is used so that the material does not chemically react. The choice of metal can minimize negative effects of chemical reactions. Nickel, stainless or [[mild steel]], or other metals can be chosen depending on the desired [[redox]] conditions. 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 [[Casting (metalworking)|casting]]s, metal powders can also be turned to compact solids by this method, the inert gas is applied between {{convert|7350|psi|MPa|abbr=on}} and {{convert|45000|psi|MPa|abbr=on}}, with {{convert|15000|psi|MPa|abbr=on}} being most common. Process soak temperatures range from {{convert|900|F|abbr=on}} for [[aluminium]] castings to {{convert|2400|F|abbr=on}} for [[nickel]]-based [[superalloy]]s. 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 (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 (metalworking)|cladding]]. Hot isostatic pressing is thus also used as part of a [[sintering]] ([[powder metallurgy]]) process and for fabrication of [[metal matrix composite]]s,<ref>{{Cite journal
| last1 = Atkinson
| first1 = Dr H. V.
| last2 = Davies
| first2 = S.
| date = 2000-12-01
| title = Fundamental aspects of hot isostatic pressing: An overview
| journal = Metallurgical and Materials Transactions A
| language = en
| volume = 31
| issue = 12
| pages = 2981–3000
| doi = 10.1007/s11661-000-0078-2
| bibcode = 2000MMTA...31.2981A
| s2cid = 137660703
| issn = 1073-5623
}}</ref>
often being used for postprocessing in [[3D printing|additive manufacturing]].<ref name="Simpson_2018-05-05">{{Citation |last=Simpson |first=Timothy W. |date=2018-05-05 |title=After the build is done why do the bills keep coming? |journal=[[Modern Machine Shop]] |url=https://www.mmsonline.com/blog/post/why-do-the-bills-keep-coming |accessdate=2018-05-18 |postscript=.}}</ref>

The process can be used to produce waste form classes. Calcined radioactive waste (waste with additives) is packed into a thin walled metal canister. The [[adsorbed]] gases are removed with high heat and the remaining material compressed to full density using argon gas during the heat cycle. This process can shrink steel canisters to minimize space in disposal containers and during transport. It was invented in the 1950s at the [[Battelle Memorial Institute]]<ref>{{Cite web |date=April 2, 1985 |title=The Evolution of HIP |url=https://www.asme.org/wwwasmeorg/media/resourcefiles/aboutasme/who%20we%20are/engineering%20history/landmarks/103-first-hot-isostatic-processing-vessels.pdf |website=ASME.org}}</ref> and has been used to prepare [[nuclear fuel]] for [[submarines]] since the 1960s. It is used to prepare inactive ceramics as well, and the [[Idaho National Laboratory]] has validated it for the consolidation of radioactive ceramic waste forms. [[ANSTO]] (Australian Nuclear Science and Technology Organisation) is using HIP as part of a process to immobilize waste [[radionuclides]] from [[molybdenum-99]] production.{{fact|date=January 2025}}

==References==
{{Reflist}}

==External links==
* [http://www.epma.com/hot-isostatic-pressing/ European Powder Metallurgy Association (EPMA) - Hot Isostatic Pressing] EPMA HIP info page

[[Category:Industrial processes]]
[[Category:Metallurgical processes]]
[[Category:Metalworking]]