Copper and Copper Alloy Powder Metallurgy Properties and Applications
By John L. Everhart
Metal Powder Industries Federation
Introduction
Powder metallurgy, the technology of utilizing metal powders, offers the engineer a means conserving materials, reducing machining and securing a uniform product at a reasonable cost. This unique metal-forming method permits the production of parts with close tolerances and a minimum of scrap. It also enables the development of products that cannot be produced by any other method. By proper selection of powders, the powder metallurgy (P/M) specialist can control the density of products over a wide range and secure a wide range of mechanical and physical properties. He can produce mixtures of metals that are insoluble in each other or mixtures of metals and nonmetals that combine the properties of both.
Density can be controlled to produce parts with porosities as high as 60% or, conversely, those that are practically pore-free and have densities approaching the theoretical density of the metal. It is also possible to vary the density in a single part. And by producing parts with interconnected pores, the metallurgist can obtain a skeleton that can be impregnated with oils, plastics or even a metal having a lower melting point.
Using Copper Powders
Copper and copper alloy powders have been used in industrial applications for many years. Probably the best known is the self-lubricating bearing which was the first major application and still accounts for about 70% of the granular copper powder used. This application takes advantage of the ability to produce a component with controlled interconnected and surface-connected porosity. The production of metallic filters also takes advantage of this ability.
Pure copper powder is used in the electrical and the electronics industries because of its excellent electrical and thermal conductivities. Alloyed with tin, zinc, nickel and other elements, copper in powder form is used in structural parts and friction materials. Brasses, bronzes and other copper alloys produced by powder metallurgy methods have the physical and mechanical properties of their cast or wrought counterparts. Copper is used also as an alloying element in iron powder components to enhance the mechanical properties and control dimensional changes during sintering, the addition being made either by mixing or by infiltration.
In addition to the above applications of granular copper powder, a large quantity of copper and copper alloy powder is used in flake form, i.e., as a powder whose thickness is small in relation to its other dimensions. Such powders are used, for example, in antifouling paints, decorative and protective coatings and printing inks.
Copper and copper alloy powders are also used in such nonstructural applications as brazing, cold soldering, and mechanical plating, as well as for medals and medallions, metal-plastic decorative products and a variety of chemical and medical purposes.