Hot isostatic pressing

Hot Isostatic Pressing (HIP) is a technique for densifying materials initially containing cavities. It involves heating and a pressurizing with a generally neutral gas: under the combined effects of these two factors, cavities are eliminated. The means of generating, containing and safely using this particular material treatment medium are first described, together with the characteristics of industrial installations in terms of capacity, implementation and variants. Next, the application of HIP as a post-treatment process for parts with residual defects is presented. These are cast or powder-metallurgy parts, whose mechanical properties (ductility, toughness, fatigue strength, etc.) are thus improved, while the dispersion of these properties is reduced. The use of HIP as a direct manufacturing technique is then detailed. In this case, the materials are introduced into sealed envelopes, and the cavities are pores (in the case of powder sintering) and/or gaps (in the case of diffusion welding). The manufacturing processes and the characteristics of powders suitable for HIP are given, as are numerous examples of applications.

These processes produce highly homogeneous, isotropic materials with excellent mechanical properties, and original components that are often complex due to their geometry and/or multi-material nature. For certain applications, HIP also saves materials by eliminating or reducing machining and welding operations.

Finally, we look at the mechanisms by which materials evolve under HIP conditions: densification, of course, but also physico-chemical and microstructural changes.

At the end of the article, readers will find a glossary of terms and a table of symbols.