What are the effects of powder properties in powder metallurgy?

What are the effects of powder properties in powder metallurgy?

Many products are produced by powder metallurgy molding process, so the performance of powder metallurgy products will not only be affected by the process, but also be limited by the raw powder. However, the properties related to powder in powder metallurgy molding are its particle size and shape, so powder metallurgy molding should be strictly controlled in these two aspects. What should I do?

A general term for all properties of a powder. It includes: geometrical properties of powder (particle size, specific surface area, pore size and shape, etc.); Chemical properties of the powder (chemical composition, purity, oxygen content, acid insoluble substances, etc.); Mechanical properties of powder (loose density, fluidity, formability, compressibility, stacking angle, shear angle, etc.); Physical properties and surface characteristics of the powder (true density, luster, wave absorption, surface activity, ze% 26mdash; ta (% 26ccedil;) Potential, magnetism, etc.). Powder properties often determine the properties of powder metallurgy products to a large extent.

The most basic geometric properties are the particle size and shape of the powder.

(1) Grain size. It affects the processing and forming of the powder, the shrinkage during sintering and the final performance of the product. The performance of some powder metallurgy products is almost directly related to the particle size. For example, the filtering accuracy of filter materials can be obtained empirically by dividing the average particle size of the original powder particles by 10; The properties of cemented carbide products are closely related to the grain size of wc phase. The particle size of the powder used in production practice ranges from hundreds of nanometers to hundreds of microns. The smaller the particle size is, the greater the activity is, and the easier the surface is to oxidize and absorb water. When it is as small as hundreds of nanometers, the storage and transportation of the powder is not easy. And when it is small to a certain extent, the quantum effect starts to work, and its physical properties will change greatly. For example, ferromagnetic powder will become superparamagnetic powder, and the melting point will also decrease with the decrease of particle size.

(2) The particle shape of the powder. It depends on the pulverizing method, such as the powder obtained by electrolysis, and the particles are dendritic; The iron powder particles obtained by the reduction method are sponge flakes; Spherical powder is basically obtained by gas atomization. In addition, some powders are egg shaped, disc shaped, needle shaped, onion shaped, etc. The shape of powder particles will affect the fluidity and loose density of the powder. Due to the mechanical engagement between particles, the compacts of irregular powder are also strong, especially the dendritic powder, which has the highest compacts strength. But for porous materials, spherical powder is the best.

Mechanical properties The mechanical properties of powders are the technological properties of powders, which are important technological parameters in powder metallurgy forming process. The loose packing density of powder is the basis for weighing by volume method during compaction; The fluidity of the powder determines the filling speed of the powder to the die and the production capacity of the press; The compressibility of the powder determines the difficulty of the pressing process and the pressure applied; The formability of the powder determines the strength of the billet.

The chemical properties mainly depend on the chemical purity of raw materials and the pulverizing method. Higher oxygen content will reduce the compactability, compact strength and mechanical properties of sintered products. Therefore, most technical conditions of powder metallurgy have certain provisions on this. For example, the allowable oxygen content of the powder is 0.2%~1.5%, which is equivalent to the oxide content of 1%~10%.

Powder shapes are various, mainly determined by the manufacturing method. Powder metallurgy molding includes dendritic, sponge flakes, spherical powder, eggs, discs, needles, onions, etc. In addition, different shapes also have an impact on the performance of the powder itself, which should be determined according to the actual situation.