Hot Isostatic Pressing
HIP (hot isostatic pressing) combines the influences of high heat and pressure to improve the mechanical properties of cast or additive manufactured parts.
What is Hot Isostatic Pressing?
In HIP, parts are heated to very high temperatures in a sealed chamber capable of generating very high pressures with an inert gas (usually argon). The combined influences of heat and pressure close pores that form when parts are cast or additively manufactured, bringing the parts as close as possible to their maximum theoretical density.
A side benefit of the process is that it’s carried out at similar temperatures as homogenization treatments. For this reason, HIP can eliminate the need to execute separate homogenization treatments in some cases.
Boosting Part Performance with Heat and Pressure
HIP is conducted in a vessel that subjects parts to very high heat and intense isostatic pressure, reducing the porosity of cast and additively manufactured parts.
How HIP Works: An Evolution
HIP was invented in the mid-1950s as a dissimilar metal diffusion bonding technique. In diffusion bonding, high heat and pressure inside a vessel cause the surfaces of distinct parts to slowly meld into one another.
Metallurgists understood that HIP could also overcome the problem of casting porosity. Casting porosity refers to small gas pores that form during metal solidification in the casting process. The pores remain after the metal solidifies, making parts weaker. HIP eliminates the pores, greatly enhancing mechanical performance.
Today, HIP is recognized as a supplement to additive manufacturing. Just as pores often form during casting, the additive manufacturing process can lead to voids in parts. Because additive manufacturing has been recognized as a viable and cost-effective way to make complex aerospace components and medical implants, HIP is in-demand.
HIP is ideal for components with critical dimensions because pressure during treatment is applied uniformly to the entire surface of the part. An inert gas—most often, it’s argon—is preferred inside the HIP vessel because it assures that part surfaces won’t react with the atmosphere.
Common examples of parts that undergo HIP include:
- Turbine blades found in jet engines or power generation facilities
- Medical implants like artificial hips, knees or vertebrae
- Metal injection-molded firearm components
Benefits of HIPing
HIP creates mechanical properties that are ideal for parts in high-temperature, high-stress service such as jet engine or gas turbine blades. Its benefits include:
- Better fatigue resistance and improved performance at extreme temperatures
- Improved resistance to impact, wear and abrasion
- Reduced porosity and increased density
- Improved ductility
- Consistent application even for parts with complex geometries
HIP Vessel Capabilities
The HIP vessel in use in Paulo’s Cleveland Division is a Quintus model QIH-122. With a 24.5-inch diameter and a 68-inch height, the vessel can reach temperatures of over 2,550°F and pressures up to 30,000psi. That’s almost twice the pressure recorded at the bottom of the Mariana Trench in the Pacific Ocean, 36,000 feet below the sea surface!
We chose our HIP model for its additional thermal processing capabilities. It comes with highly controllable rapid-cool features and can HIP and solution treat parts at the same time.
Advance Your Processing, Advance Your Results
If you’re interested in a more in-depth discussion about how HIP can enhance your parts, tell us a little about your project to get connected with the Paulo expert who can help.Get Started