powder metallurgy (redirected from infiltrated)

powder metallurgy

Fabrication of metal objects from a powder rather than casting from molten metal or forging at softening temperatures. In some cases the powder method is more economical, as in making metal parts such as gears for small machines, in which casting would involve considerable scrap loss. In other cases, melting is impractical (e.g., because the melting point of the metal is too high). Powder metallurgy is also used to produce a porous product that will allow a liquid or gas to pass through it. See also metallurgy, sintering.

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powder metallurgy [′pau̇d·ər ′med·əl‚ər·jē]

(metallurgy)

A metalworking process used to fabricate parts of simple or complex shape from a wide variety of metals and alloys in the form of powders. The process involves shaping of the powder and subsequent bonding of its individual particles by heating or mechanical working.

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Powder metallurgy

A metalworking process used to fabricate parts of simple or complex shape from a wide variety of metals and alloys in the form of powders. The process involves shaping of the powder and subsequent bonding of its individual particles by heating or mechanical working. Powder metallurgy is a highly flexible and automated process that is environmentally friendly, with a low relative energy consumption and a high level of materials utilization. Thus it is possible to fabricate high-quality parts to close tolerance at low cost. Powder metallurgy processing encompasses an extensive range of ferrous and nonferrous alloy powders, ceramic powders, and mixes of metallic and ceramic powders (composite powders). See Metallurgy

Regardless of the processing route, all powder metallurgy methods of part fabrication start with the raw material in the form of a powder. A powder is a finely divided solid, smaller than about 1 mm (0.04 in.) in its maximum dimension. There are four major methods used to produce metal powders, involving mechanical comminution, chemical reactions, electrolytic deposition, and liquid-metal atomization. Metal powders exhibit a diversity of shapes ranging from spherical to acicular. Particle shape is an important property, since it influences the surface area of the powder, its permeability and flow, and its density after compaction. Chemical composition and purity also affect the compaction behavior of powders.

Powder metallurgy processes include pressing and sintering, powder injection molding, and full-density processing. See Sintering

Normally, parts made by pressing and sintering require no further treatment. However, properties, tolerances, and surface finish can be enhanced by secondary operations such as repressing, resintering, machining, heat treatment, and various surface treatments.

Powder injection molding is a process that builds on established injection molding technology used to fabricate plastics into complex shapes at low cost. It produces parts which have the shape and precision of injection-molded plastics but which exhibit superior mechanical properties such as strength, toughness, and ductility.

Parts fabricated by pressing and sintering are used in many applications. However, their performance is limited because of the presence of porosity. In order to increase properties and performance and to better compete with products manufactured by other metalworking methods (such as casting and forging), several powder metallurgy techniques have been developed that result in fully dense materials; that is, all porosity is eliminated. Examples of full-density processing are hot isostatic pressing, powder forging, and spray forming.

Powder metallurgy competes with several more conventional metalworking methods in the fabrication of parts, including casting, machining, and stamping. Characteristic advantages of powder metallurgy are close tolerances, low cost, net shaping, high production rates, and controlled properties. Other attractive features include compositional flexibility, low tooling costs, available shape complexity, and a relatively small number of steps in most powder metallurgy production operations.

Metal powders can be thermally unstable in the presence of oxygen. Very fine metal powders can burn in air (pyrophoricity) and are potentially explosive. Some respirable fine powders pose a health concern and can cause disease or lung dysfunction. Control is exercised by the use of protective equipment and safe handling systems such as glove boxes. See Industrial health and safety