Bodycote Hot Isostatic Pressing

HOT ISOSTATIC PRESSING (HIP) OFFERS THE POSSIBILITY OF ELIMNATING CLOSED POROSITY, VOIDS AND CREEP VOIDS IN CAST COMPONENTS.

HIP can also improve the homogeneity of the microstruc-ture and the material properties.

This is especially important in the case of cast parts which are exposed to very high dynamic stresses and subject to a corrosive environment (the human body), such as cobalt chrome knee and hip implants.

In this application hot isostatic pressing also enhances the bonding of biocompatible coatings.

The Bodycote HIP group offers the service of HIP as an integral part of the production route for high quality investment castings.

Principle

Compared to the forging route investment casting offers the attractive possibility of producing cost effective near net shape parts.

One disadvantage is that because of internal porosity the properties of the parts may not be as good as those obtained from forged material.

The application of a high temperature, high pressure gas environment provides the means by which internal porosity can be removed, utilising plastic yielding, creep and diffusional effects.

Diffusion bonding of the void surfaces during the final stage of densification ensures that defects are completely removed.

Medical Implants

Over the last few years a number of technical advances have been introduced into medical implants to improve and extend their life in service.

For example, small beads may be sintered or cast onto the body of the vacuum cast cobalt-chrome or titanium implant.

This forms a porous coating into which bone tissue will grow, achieving full osteo-integration of the prosthesis.

Such components may be HIPped after the coating is applied in order to improve the integrity of the coating as well as to remove internal porosity thus improving mechanical properties.

The HIP treatment also provides improved homogenisation of the cast stucture.

Advantages

As well as improving mechanical properties, the elimination of porosity by HIP assists in the achievement of pore free polished wear surfaces, improving friction characteristics and reducing the inititiation of corrosion.

Not only is the process beneficially applied to cast cobalt chrome, titanium and stainless steel implants but is also regularly used to improve the density of hot pressed ceramic implants and is used as a powder compaction technique to produce fine grained cobalt chrome billets for the forging of medical implants.

Applications:

Cast cobalt chrome implants

Cast titanium implants

Cast stainless steel implants

Pressed and sintered ceramic implants

PM cobalt chrome forging billets

Coating enhancement