Development and application of powder metallurgy production


Modern powder metallurgy production was started in the early 20th century when an American called W.D.Coolidge firstly made tungsten powder by reducing tungsten oxide with hydrogen so as to produce tungsten filament. Since then, copper powder, cobalt powder, nickel powder, iron powder, tungsten carbide powder and other various metal powders were produced by chemical reduction method, which promoted the development of early metal powder metallurgy products (porous bearing, porous filter, cemented carbide and so on); at this time, carbonyl process was also developed so as to produce iron powder and nickel powder.

metal powder products companyIn 1930’s, vortex grinding method and carbon reduction method were successively used in producing iron powder, which both took very low cost. Besides, molten metal atomization method was also emerged in the early 1930’s, which was used in producing low melting point metals, such as tin powder, lead powder, aluminum powder and other metal powders. In the early 1940’s, high pressure air atomization method was used in producing iron powders. In the early 1950’s, high pressure water atomization method was begun to be used in producing alloy steel and many other alloy powders. In 1960’s, various atomization methods were used in producing high alloy powders, which promoted the development of high-performance powder metallurgy products. Since 1970’s, various gas phase and liquid phase physical-chemical reaction methods have been used in producing coated powders and superfine powders that have important usages.

Metal powder belongs to incompact substance. The metal powder performance will comprehensively reflect the metal property, single particle character and particle swarm specialty. Generally speaking, the performance of metal powder can be divided into chemical property, physical property and processing property. Chemical property refers to metal content and impurity content, physical property mainly includes average particle size and size distribution, specific surface and true density as well as particle shape, surface appearance and internal microstructure, while processing property is a kind of combination property, which mainly includes powder mobility, apparent density, tap density, compressibility, formability and size variation in sintering.

In addition, in some special usages, other chemical and physical properties of powder are also required, such as catalytic property, electrochemical activity, corrosion resistance, electromagnetic property, internal friction coefficient and so on. Metal powder metallurgy performance will largely depend on the powder production method and preparation technology. Powder basic performance can be measured by specific standard testing method. Powder particle size and size distribution can be measured by many ways, in which sieve analysis (when the powder particle size is more than 44μm), sedimentation analysis (when the powder particle size is 0.5100μm), gas permeability method and microscopic method are generally used. Superfine powder (the particle size is less than 0.5μm) can be measured by electron microscope and small angle X-ray scattering. Metal powder is usually divided into coarse powder, medium powder, fine powder, micro powder and superfine powder.