Isostatic pressing ceramic

- May 07, 2020-

Isostatic pressing is a powder metallurgy (PM) forming process that applies equal pressure in all directions on a powder compact thus achieving maximum uniformity of density and microstructure without the geometrical limitations of uniaxial pressing.

 

Isostatic pressing is performed "cold" or "hot." Cold isostatic pressing (CIP) is used to compact green parts at ambient temperatures, while hot isostatic pressing (HIP) is used to fully consolidate parts at elevated temperatures by solid-state diffusion. HIP can also be used to eliminate residual porosity from a sintered PM part.


Hot isostatic pressing (HIP) and cold isostatic pressing (CIP) technology has been known for more than 50 years, and is considered today to be a standard production route for many applications. The HIP process applies high pressure (50-200 MPa) and high temperature (400-2,000°C) to the exterior surface of parts via an inert gas (e.g., argon or nitrogen). The elevated temperature and pressure cause sub-surface voids to be eliminated through a combination of plastic flow and diffusion. The challenge is to reach the highest possible theoretical density while maintaining productivity goals.

The CIP process applies an even higher pressure to metal or ceramic powders, typically 100-600 MPa at ambient temperature or slightly elevated temperatures(< 93°C), to achieve “green” parts with enough strength to be handled, machined, and consequently sintered to final strength. Uniform rapid cooling* is a process by which thin-walled pre-stressed wire-wound HIP units increase productivity up to 70% compared with natural cooling, and increase the density to ~ 100% of theoretical density for many alloys. The added cost to reach this density is around $0.20-0.30/kg for a large production HIP system, depending on the material.

HIP and CIP technologies provide manufacturers with opportunities to control their material properties and increase productivity. Productivity is increased two-fold through the use of uniform rapid cooling. The quality of ceramic “green” compacts is greatly improved through the use of fine-tuned decompression systems. In addition, combining HIP and heat treatment in the same equipment results in shorter lead times, better material properties, and processing and investment cost savings.