The process of Hot Isostatic Pressing

Hot Isostatic Pressing

Hot isostatic pressing (also called HIP or HIPing) is a special manufacturing process that consolidates material and closes pores within parts through the application of heat and pressure. HIP is an established process within Aalberts Surface Technologies in the EU and the US.

depending on your application, there are different process options, with the goal of achieving the desired properties.

HIP uses a furnace inside a pressure vessel and is the simultaneous application of heat and a high pressure inert gas (usually Argon) to materials. The simultaneous application of heat (up to 1250°C) and pressure (up to 207 MPa, 2070 bar) eliminates internal voids and microporosity (no connectivity to the surface) through a combination of plastic deformation, creep, and diffusion bonding. The furnace chamber is heated causing the pressure inside the vessel to increase. Many systems use associated gas pumping to achieve the high pressure level. The gas pressure is applied to the material from all directions (hence the term “isostatic”).

Applying heat and pressure simultaneously eliminates internal voids and defects such as porosity in castings (investment casting) and lack-of-fusion defects in additively manufactured (AM) parts. HIP is effective with almost all materials – including metals, ceramics, and plastic – and can be applied to a large range of alloys including nickel, titanium, steels, aluminum, copper, and magnesium. It improves materials properties such as fatigue resistance, creep, ductility, and workability of parts designed for mission-critical applications. The HIP process densifies, repairs, and creates a uniform microstructure and is the ideal process to improve the reliability and performance of your product by eliminating porosity achieving 100% theoretical density.

As the high pressure atmosphere acts in an isotropic manner on the surfaces of components in the hot zone, the mechanical force exerted is even. This means that solid parts do not see any geometrical change in the HIP. The gas presses on internal cooling channels in the same way as long as they are open to the gas, i. e. with connectivity to the surface. Casting, MIM and AM parts are all possible to HIP, and canned powders can be formed into solid components. In Powder Metallurgy (PM), the HIP process can produce near net shape materials from canned metallic compositions that are difficult or impossible to forge or cast.

HIP is used for the densification and elimination of internal porosity in cast, additive manufactured (AM) and sintered material

Mechanisms: Mechanical deformation / Creep / Diffusion

Isostatic pressure conditions
Inert gas as pressure medium, usually Argon
Same pressure acting on all surfaces in all directions

simultaneous application

Simultaneous application of a high-pressure gas and an elevated temperature. In a specially constructed vessel, the pressure applied is isostatic because it is developed with a gas Under these conditions of heat and pressure internal defects within a solid body collapse and weld up

microstructure pre HIP en post HIP

Two halves of a cylinder, each with a drilled 1” diameter hole welded together Potential dimension change depends on vol.% of porosity 1% Porosity 1% Shrinkage by volume Shrinkage is evenly distributed if porosity is evenly distributed.

FAQ

What is Hot Isostatic Pressing (HIP)?

HIP uses a furnace inside a pressure vessel. Very high pressure gas, usually argon at elevated temperature, is used to consolidate material and remove internal defects such as porosity and microcracks. As HIP uses temperatures very close to those used for heat treatment, creep and diffusion occur, along with mechanical deformation of defects due to extreme external pressure.

What is the effect of HIP?

As HIP removes internal defects in the load, material properties such as fatigue life, elongation and impact toughness are improved. Subsequent grinding of polishing of surfaces demonstrates excellent roughness values and no unwanted porosity is uncovered by these operations. The HIP has already fixed those.

What parameters should be used?

Modern HIP equipment from Quintus operates up to 2000°C (3632°F) and 200MPa (30,000 psi). The parameters chosen are material specific, and often an increased pressure can allow lower temperatures to be used, preserving the material microstructure. Of course, the HIP cycle used should not exceed the melting temperature of the material to be treated.

Which materials can be HIPed?

HIP is used to consolidate powders, solids and combinations thereof. Materials range from ceramics to metals and composite materials. Lightweight materials, high speed steels, tool steels and super alloys all use HIP, and new generations of materials such as high entropy alloys are also developed using this process.

Can any products be HIPed?

As the high pressure atmosphere acts in an isotropic manner on the surfaces of components in the hot zone, the mechanical force exerted is even. This means that solid parts do not change shape in the HIP. The gas presses on internal channels in the same way as long as they are open to the gas. Casting, MIM and AM parts are all possible to HIP, and canned powders can be formed into solid components (PM HIP or PM NNS, Powder Metallurgy Near Net Shape).