This specification covers a wide range of parts that are produced by the powder metallurgy process which consists of compressing and sintering certain metal powders. In some cases, the parts have inherent characteristics not obtainable by other methods of fabrication such as with bearings where the porous structure permits self-lubrication, with filters where pore size or permeability may be well controlled, and with brake linings where temperature stability and wear resistance may be built-in. In other cases the parts are produced more economically such as with structural and functional parts whose shape would otherwise require costly machining operations and high scrap loss.
The metals most commonly used in powder metallurgy are iron, copper, and tin; and to some extent lead. Nickel, nickel-silver, brass, stainless steel and other metals are also used. In some cases, small additions of carbon are used to increase hardness and strength or to achieve other desirable properties. The addition of certain other alloying elements increases the hardenability when parts are heat treated. Pure-iron, or special alloys of iron may be used to achieve magnetic properties. Certain non-metallic materials are sometimes mixed with the metal powders to enhance frictional characteristics, to facilitate compression and ejection of the compacted part from the die, or to serve as a lubricant or anti-galling agent in the finished part.