Powder Metallurgy
Powder metallurgy (PM) is materials processing technology used to fabricate nearly all metal components. Through the application of this technology, components are formed from metallic powders by compaction, sintering, and sometimes, a combination of both. Compaction is the process of purposively forming a dry powder into organized structures that mimic the shapes of the manufactured components.
The process begins with a mass of powdered metal, typically containing minus 200 mesh (75 µm) particles, that is blended with appropriate amounts of lubricants and sometimes, other additives prior to the compaction cycle. The use of ultrafine metal powders is an example of a relatively recent PM development. Ultrafine metal powders that are used in PM applications range from minus 325 mesh or even smaller. During compaction, the powder is inserted into a metal die. The powder is then pressed into the cavity of the die by applying a uniaxial pressure, usually in the range of 10 to 30 tons per square inch (150-430 MPa) of the cross sectional area of the die.
Sintering is the process of purposively binding metal particles together at temperatures below the melting point of the base material. At elevated temperatures and under certain conditions, particles can be made to adhere to each other through a process of diffusion, wherein intermetallic bonds form at the interface of the particles. During this process, the particles can also attain plastic deformation, causing further displacement and displacement of the particles.
To achieve the desired metallurgical properties, the sintering temperature is carefully selected, allowing a material’s inherent properties to be fully developed within the sintered microstructure. After sintering, the part is machined to its finished configuration.
The combination of compaction and sintering is referred to as “warm compaction or hot pressing”, wherein the powder is simultaneously compressed and sintered within a heated die. During warm compaction, compaction pressure is applied while the die is above the sintering temperature of the material being processed.
The greatest advantage of utilizing powder metallurgy technology is the ability of the process to produce components that can be given complex shapes and near net-shapes.
The benefits of such a process include low levels of scrap; geometric shapes limited only by the die tool design; high reproducibility; economy in raw materials and energy; the possibility of introducing alloys; and the ability to produce components of closely controlled tolerances.
PM has a wide application in the creation of components from a range of materials including stainless steel, brass, bronze, titanium, magnesium, aluminum, and other metals. It also find its use in producing intermetallics and ceramic composites as well as components containing magnetic and electrical properties. PM parts are used in numerous products including bearings, gears, and locks.
Conclusion
Powder Metallurgy technology has been proven to enable the production of components with very tight tolerances, complex geometries, and near net-shapes. The process is also economical in terms of both raw materials and energy. It finds many applications in the creation of components from a range of materials and also in producing intermetallics, ceramic composites as well as components containing magnetic and electrical properties.
