What is the purpose of copper infiltration into a PM component, and how is it accomplished?

Components are copper infiltrated for a number of reasons. Some basic desired results are improvements to tensile strength, hardness, impact properties, and ductility. Copper-infiltrated components will also have a higher density. 

Other reasons customers may elect copper infiltration are for wear improvement or to block air/gas flow through an otherwise porous component at temperatures that a resin may not be practical.  Sometimes copper infiltration is used to enhance the machining characteristics of PM steel; the copper leaves a smoother machined finish.

Here’s how copper infiltration works:

The base structure of the component has a known density, which is used to determine the amount of open porosity. A measured amount of copper is selected matching the amount of porosity to be filled. The copper fills the porosity during the sintering process (at temperatures above the melt temperature of copper) simply by placing the copper against the component prior to sintering. The >2000°F sintering temperature allows for the molten copper to flow into the component porosity through capillary action. Sintering is completed on a carrier (e.g. ceramic plate) so the copper stays on the component. Once the part is cooled, the copper is solidified within the structure.

Top Photo (right): Parts assembled with copper slugs ready for sintering. (Photo by Atlas Pressed Metals)

Bottom Photo (right): Microstructure of a part showing how copper infiltrates open porosity. (Photo by Dr. Craig Stringer – Atlas Pressed Metals)