Process Description
The pack cementation, or pack diffusion, process diffuses the coating material into the substrate, generally to impart oxidation and high temperature corrosion resistance to the coated part. Most often, the coating material is a powder of aluminum, chromium cobalt or alloys of these materials.

The parts to be coated are placed in a retort or sled in a mixture of the coating material and an inert powder, such as aluminum oxide, along with a halide salt. The retort is then placed in a protective atmosphere (hydrogen or argon) furnace and brought up to the coating temperature. The salt vaporizes and combines with the coating to generate the transporting vapor species. The retort is placed in a furnace and brought to a temperature at which the coating material will react with the salt to form a metallic halide vapor, which comes in contact with the surface of the parts to form the coating.

Depending on the coating material chosen, the concentration of the coating material in the pack and the time and temperature of the diffusion cycle, various coating structures and diffusion zones form in a controlled manner.

Features of the Pack Cementation Process
• Metallurgically bonded to the substrate
• Batch processing for high production rates
• Can be used to coat large or small components
• Coats both external and internal surfaces, even deep, small bores
• Can be tailored to meet specific requirements
• Economical process