Casting densification

Hot isostatic pressing (HIPing) for densification of metal castings occurs by application of gas pressure at an elevated temperature where internal microporosity is eliminated by plastic deformation and diffusion bonding.

Benefits

• HIP improves product consistency with less variation in mechanical properties.
• Typically tensile and proof strengths increase by around 5% and ductility by up to 50%, although the degree of casting property improvement is dependent on many parameters including the initial as cast quality.
• Fatigue properties significantly increase following HIP with up to tenfold fatigue life improvements achieved, producing properties comparable to similar wrought alloys.
• Impact strength, toughness, and machined surface finish are all enhanced.
• Property improvements may allow castings to be considered for new applications and/or allow a redesign of existing components to a more cost effective solution.
• Shrinkage defects, creep voids and internal cracks are removed.
• HIP allows recovery of castings that would otherwise be rejected based on x-ray inspection.
• By eliminating microporosity, HIP removes fatigue crack initiation sites.

Application & materials

Examples of castings HIPed in large volumes include, but are not limited to: Hot section and structural gas turbine components (both dynamic and static); aerospace structural and engine parts; implantable medical devices; automotive engine components; valve bodies and other petrochemical processing equipment; critical munitions pieces; and tooling, die and general engineering parts.

Every week a typical Bodycote HIP plant will process many tons of titanium, aluminium, steel and superalloy castings. Most cast metals can be HIPed such as stainless steel and alloys of nickel, cobalt, titanium, chromium, aluminium, copper and iron. A few materials may be unsafe due to safety or cross-contamination risks (e.g. lead and cadmium).

Process details

During the HIP process, castings are subjected to elevated pressure and temperature for a prescribed length of time. This allows surrounding material to flow into internal pores and diffusion to occur to eliminate the voids. Pressure is applied by a high purity inert gas so the casting composition is not affected. Bodycote works closely with customers to meet their specifications and to determine optimum processing parameters.