Powder metallurgy (PM) is an industrial method for obtaining metal or metal-like powders, molding semifinished goods from powders, and manufacturing particles from them by a thermal process, called sintering. The sintering temperature is below the melting temperature of the main component in the powder mixture. Because of the similarities between methods for ceramic (shaping – thermal treatment) and PM (molding – sintering) production, the end bodies produced by PM are also called metalloceramics.
The term “powder metallurgy” sounds provocative or at least suspicious on the pages of a publication when the author wants to propagandize the achievements of a technology, the first step of which is metal or ceramic powder production. Could a technology be connected with powder production and its processing in a way that is friendly to both environment and humanity, especially when our every-day practice shows that metallurgy is a main natural pollutant?
The first historical example for industrial applications of PM is the chiseling of high-quality platinum (Pt) coins by intaglio. The method was developed by Sobolevski and Liubarski in Russia and practiced from 1826 to 1844. The first modern powder metallurgy product was the tungsten (W) filament of electric light bulbs, developed in the early 1900s. During this time, the production of materials and products was closely related to the achievements of the necessary technological conditions, primarily the realization of high temperatures and the reliability of the corresponding equipment and materials. Although the process has existed for more than 100 years, over the past quarter century it has become widely recognized as a superior way to produce high-quality parts for a variety of important applications. This success is due to the privileges that the PM process offers over other metal-forming technologies (such as forging and metal casting), advantages in material utilization, shape complexity, and near-net shape dimensional control. These, in turn, yield benefits of lower costs and greater production versatility.
PM is closely connected with technologies that determine its relationship to environmental protection. Obtaining and manipulating solids in powder state is an essential feature of PM. If PM is limited to the production of metal or metal-like powders, it would be just a part of metallurgy and could not be a progressive, technologically, and economically attractive method combined with metallurgy, materials science, and metalworking. Elimination (in most cases) or at least minimization of machining of the end article leads to economic advantages. As more than 97% of the starting materials reach the finished product, powder metallurgy is a process that conserves both energy and materials. Elimination of scrap losses, which directly reflects on environmental protection, is another privilege of the PM method, providing many possibilities to create waste-free and environmentally friendly processes.
Advantages and Applications of PM
PM could use wastes obtained by other traditional metallurgical processes. The utilization of copper oxides obtained after cable production is a good example. This simple technology allows the burning of engine oil, presented as an impurity, to obtain pure fragile copper oxide flakes. After milling of copper oxide and reduction with hydrogen at 450 °C, one obtains pure copper (Cu) powder of very high quality that is suitable for use in the electrical industry for production of copper-graphite brushes. Controlling the parameters of the processes of milling and reduction (type of mill, milling conditions, time, and temperature), one could obtain Cu powder with defined chemical, physical, and technological properties. In this example, another advantage of PM is demonstrated — the creation of composite materials from physically and chemically different (as copper and graphite) components. Very often, PM is the only technology able to lead to the production of materials and articles with specific properties, such as self-lubricating bearings, hard alloy cutting tools from tungsten carbide (WC)-based alloys, magnet materials, copper-graphite brushes for electric engines, catalysts, and hydrogen storage materials for hydrogen economics, among others.
From: “Powder Metallurgy: Problems of an Economically Friendly Technology”