Copper infiltration is a method that is commonly used in PM to fill the open porosity in a steel PM compact in an effort to either increase the strength of the part or to seal porosity for a pneumatic or hydraulic application (or both). An article in Industrial Heating Magazine has a good technical definition of the infiltration process:
“Infiltration is basically defined as "a process of filling the pores of a sintered or unsintered compact with a metal or alloy of a lower melting point." In the particular case of copper infiltrated iron and steel compacts, the base iron matrix, or skeleton, is heated in contact with the copper alloy to a temperature above the melting point of the copper, normally within the range of 2000¯ to 2100¯F (1095¯ to 1150¯C). Through capillary action, the molten copper alloy is drawn into the interconnected pores of the skeleton and ideally fills the entire pore volume”
For further information on copper infiltration, you can read more through this link:
https://www.industrialheating.com/articles/83856-a-description-of-the-copper-infiltration-process-used-in-iron-based-p-m-parts