Article | REF: M3310 V1

Hot isostatic pressing

Author: Emmanuel RIGAL

Publication date: December 10, 2017, Review date: October 23, 2020

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ABSTRACT

Hot Isostatic Pressing is a technique used to densify materials. Vessels, designed according to different possibilities, are often larger than 1 m3 and allow a high neutral gas pressure and a high temperature to be achieved. They are used to process parts having residual defects, thereby providing improved mechanical properties (cast parts, powder metallurgy parts). They are also used to sinter loose powder and/or to achieve diffusion welds. Materials and applications of various kinds are concerned. In this article, these uses of HIP are described and mechanisms involved in the processes are introduced.

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AUTHOR

  • Emmanuel RIGAL: Research engineer - Liten, CEA-Grenoble, Grenoble, France

 INTRODUCTION

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.

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KEYWORDS

powder metallurgy   |   hot isostatic pressing   |   casting   |   diffusion welding


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Hot isostatic pressing