The characteristics of metal powder have great influence on the pressing, sintering process, pre-sintering strength and final product performance.

The basic properties of metal powders include chemical composition, particle size distribution, particle shape and size, and technical characteristics.

1) chemical composition the chemical composition of a powder usually refers to the content of major metals or components, impurities and gases. The content of main metals in metal powder is not less than 98% to 99%, which can completely meet the requirements of sintering machinery parts. However, in the manufacture of high performance p/m materials, higher purity powder is needed.

The most common inclusions in metallic powders are oxides. The oxide makes the compressibility of the metal powder worse and increases the wear of the die. Sometimes, a small amount of reducible metal oxide is beneficial to the sintering of metal powders. Since metal powders are larger and smaller than the surface, a large amount of gas is adsorbed on the surface of metal particles. There is also a lot of gas dissolved in the metal powder making process. The main gases contained in metal powders are oxygen, hydrogen, carbon monoxide and nitrogen. These gases increase the brittleness of metal powders and make them brittle and compressible, especially plastic deterioration of refractory metals and compounds such as Ti, Zr, Cr, carbides, borides and silicides. When heated, the gas precipitates strongly, which may affect the normal shrinkage of the blank during sintering. Therefore, some metal powders are often treated by vacuum degassing.

2) particle shape and size particle shape is one of the factors influencing the technical characteristics of the powder (such as loose packing density, fluidity, etc.). Usually, the powder particles are spherical or granular. Particle size is usually expressed as particle size. The size of powder manufactured in industry is usually 0.1-500 micrometers, and those above 150 micrometers are regarded as coarse powder, 40-150 micrometers as medium powder, 10-40 micrometers as fine powder, 0.5-10 micrometers as very fine powder, and those below 0.5 micrometers are called ultrafine powder. The size of the powder particles is usually indicated by the screen number, which indicates the number of mesh holes per 1 square inch of screen.

The size of powder directly affects the properties of powder metallurgy products, especially for cemented carbide and ceramic materials. But making fine powder is difficult and economical.