Powder metallurgy has a unique chemical composition and mechanical and physical properties that are not available with conventional fusion casting methods. The use of powder metallurgy technology can directly produce porous, semi-dense or fully dense materials and products, such as oil-impregnated bearings, gears, cams, guides, tools, etc., is a less cutting process.
(1) Powder metallurgy technology can minimize the segregation of alloy components and eliminate coarse and uneven cast structure. Preparation of high performance rare earth permanent magnet materials, rare earth hydrogen storage materials, rare earth luminescent materials, rare earth catalysts, high temperature superconducting materials, new metal materials (such as Al-Li alloy, heat resistant Al alloy, super alloy, powder corrosion resistant stainless steel, powder High-speed steel, high-temperature structural materials such as intermetallic compounds, etc.) play an important role.
(2) A series of high-performance non-equilibrium materials such as amorphous, microcrystalline, quasicrystal, nanocrystalline and supersaturated solid solution can be prepared, which have excellent electrical, magnetic, optical and mechanical properties.
(3) It is easy to realize various types of recombination, and give full play to the respective characteristics of each component material, and is a process technology for producing high-performance metal-based and ceramic composite materials at low cost.
(4) It can produce materials and products with special structure and performance that cannot be produced by ordinary smelting methods, such as new porous biological materials, porous separation membrane materials, high-performance structural ceramic abrasives and functional ceramic materials.
(5) Near net formation and automated mass production can be achieved, thereby effectively reducing production resources and energy consumption.
(6) It can make full use of ore, tailings, steelmaking sludge, rolling steel scales, and recycling waste metal as raw materials. It is a new technology that can effectively carry out material regeneration and comprehensive utilization.
Our common machining tools, hardware grinding tools, many are made by powder metallurgy technology.

(1) Production of powder. The production process of the powder includes the steps of preparing the powder, mixing the powder, and the like. Plasticizers such as engine oil, rubber or paraffin are usually added to improve the moldability and plasticity of the powder.
(2) Press molding. The powder is pressed into a desired shape under a pressure of 15-600 MPa.
(3) Sintering. It is carried out in a high temperature furnace or a vacuum furnace which protects the atmosphere. Sintering differs from metal melting in that at least one element remains in the solid state during sintering. During the sintering process, a series of physical and chemical processes, such as diffusion, recrystallization, fusion welding, compounding and dissolution, become metallurgical products with a certain porosity.
(4) Post-processing. In general, sintered parts can be used directly. However, some parts requiring high precision and high hardness and wear resistance are subjected to post-sintering treatment. Post-treatment includes coining, rolling, extrusion, quenching, surface hardening, oil immersion, and infiltration.

Powder preparation method

Making powder is the first step in powder metallurgy. Powder metallurgy materials and products continue to increase, and its quality continues to increase, requiring more and more types of powders. For example, from the viewpoint of the material range, not only metal powder but also alloy powder, metal compound powder, etc. are used; from the viewpoint of powder shape, it is required to use powders of various shapes, such as when a filter is produced, it is required to form a powder; In terms of particle size, powders of various particle sizes are required, and the coarse powder has a particle size of 500 to 1000 μm and an ultrafine powder particle size of less than 0.5 μm.
In order to meet various requirements for powders, there are various methods for producing powders which are merely capable of converting a metal, an alloy or a metal compound into a powder state in a solid, liquid or gaseous state. Various methods for preparing powders and powders prepared by various methods.

Methods for converting metals and alloys or metal compounds into powders in a solid state include:

(1) Mechanical pulverization and galvanic corrosion methods for preparing metal and alloy powders from solid metals and alloys:
(2) Reduction method for preparing metal and alloy powders from solid metal oxides and salts. Reduction-chemical treatment of metal compound powders from metal and alloy powders, metal oxides and non-metal powders

The method of converting a metal to an alloy or a metal compound into a powder in a liquid state includes:

(1) Atomization method for preparing alloy powder from liquid metal and alloy
(2) Displacement method and solution hydrogen reduction method for preparing metal alloy and coating powder from metal salt solution replacement and reduction; molten salt determination method for preparing metal powder by precipitation from metal molten salt; from auxiliary metal bath A metal bath method for precipitating a metal compound powder.
(3) An aqueous solution electrolysis method for preparing a metal and an alloy powder by electrolysis from a metal salt solution; and a molten salt electrolysis method for preparing a metal and a metal compound powder from metal molten salt electrolysis.

A method of converting a metal or a metal compound into a powder in a gaseous state:

(1) a steam condensation method for preparing metal powder from metal vapor condensation;
(2) Carbon-based thermal dissociation method for dissociating gaseous metal carbon substrates from metals, alloys and coated powders
(3) A gas phase hydrogen reduction method for preparing a metal, an alloy powder, and a metal or alloy coating from a gas phase reduction of a gaseous metal halide; and a chemical vapor deposition method for preparing a metal compound powder and a coating from a gaseous metal halide deposition.
However, from the essence of the process, the existing milling methods can be broadly classified into two major categories, mechanical and physical chemical methods. The mechanical method is a process in which the raw material is mechanically pulverized and the chemical composition is substantially unchanged; the physical chemical method is a process of obtaining a powder by changing the chemical composition or aggregation state of the raw material by chemical or physical action, powder Many production methods From the industrial scale, the most widely used Hans reduction method, atomization method and electrolysis method, such as vapor deposition method and liquid phase deposition method, are also important in special applications.

The basic processes of the powder metallurgy process are:

1. Preparation of raw material powder. Existing milling methods can be broadly classified into two categories: mechanical methods and physical chemical methods. The mechanical method can be divided into: mechanical pulverization and atomization method; physical chemistry method is further divided into: electrochemical corrosion method, reduction method, chemical law, reduction-chemical law, vapor deposition method, liquid phase deposition method and electrolysis method. Among them, the most widely used methods are reduction, atomization and electrolysis.
2. The powder is formed into a compact of the desired shape. The purpose of the forming is to produce a compact of a certain shape and size and to have a certain density and strength. The molding method is basically divided into press molding and pressureless molding. The most widely used in press molding is compression molding. In addition, 3D printing technology can also be used for the production of embryo fragments.
3. Sintering of the compact. Sintering is a key process in powder metallurgy processes. The formed green compact is sintered to obtain the desired final physical and mechanical properties. Sintering is further divided into unit system sintering and multi-component sintering. For solid phase sintering of unit and multicomponent systems, the sintering temperature is lower than the melting point of the metals and alloys used; for multiphase liquid phase sintering, the sintering temperature is generally lower than the melting point of the refractory component, and higher than the fusible component. Melting point. In addition to ordinary sintering, there are special sintering processes such as loose sintering, melt immersion, and hot pressing.
4, the subsequent processing of the product. The post-sintering treatment can be carried out in various ways depending on the requirements of the product. Such as finishing, oil immersion, machining, heat treatment and plating. In addition, in recent years, some new processes such as rolling and forging have also been applied to the processing of powder metallurgy materials after sintering, and have achieved satisfactory results.

Property of powder

A general term for all properties of powder. It includes: the geometric properties of the powder (particle size, specific surface, pore size and shape); the chemical properties of the powder (chemical composition, purity, oxygen content and acid insolubles, etc.); the mechanical properties of the powder (loose density, fluidity) , formability, compressibility, stacking angle and shear angle, etc.; physical properties and surface properties of the powder (true density, gloss, absorbing, surface activity, ze%26mdash; ta (%26ccedil;) potential and magnetic properties, etc.) ). Powder properties often determine the performance of powder metallurgy products to a large extent.

The most basic geometric performance is the particle size and shape of the powder.

(1) Particle size. It affects the processing of the powder, the shrinkage during sintering, and the final properties of the product. The performance of some powder metallurgical products is almost directly related to the particle size. For example, the filtration accuracy of the filter material can be empirically determined by dividing the average particle size of the original powder particles by 10; the properties of the cemented carbide product are very similar to those of the wc phase. In the big relationship, it is only possible to obtain a fine-grained cemented carbide with a finer-grained wc material. Powders used in production practice range in size from a few hundred nanometers to hundreds of microns. The smaller the particle size, the greater the activity and the easier the surface is to oxidize and absorb water. When it is as small as a few hundred nanometers, the storage and transport of the powder is not easy, and when it is small to a certain extent, the quantum effect begins to function, and its physical properties will change greatly. For example, the ferromagnetic powder will become superparamagnetic. Powder, the melting point also decreases as the particle size decreases.
(2) The particle shape of the powder. It depends on the milling method, such as the powder obtained by electrolysis, the particles are dendritic; the iron powder particles obtained by the reduction method are in the form of sponge sheets; the gas atomization method is basically a spherical powder. In addition, some powders are ovoid, disc-shaped, needle-shaped, onion-like, and the like. The shape of the powder particles affects the fluidity and bulk density of the powder. Due to the mechanical meshing between the particles, the strength of the green compact of the irregular powder is also large, and in particular, the dendritic powder has the highest strength of the pressed compact. However, for porous materials, it is best to use spherical powder.

Mechanical properties The mechanical properties of the powder, ie the process properties of the powder, are important process parameters in the powder metallurgy forming process. The bulk density of the powder is the basis for volumetric weighing during pressing; the fluidity of the powder determines the filling speed of the powder and the productivity of the press; the compressibility of the powder determines the ease of pressing and the application of pressure. High and low; and the formability of the powder determines the strength of the blank.

The chemical properties mainly depend on the chemical purity of the raw materials and the milling method. Higher oxygen content will reduce the pressing properties, the strength of the compact and the mechanical properties of the sintered product, so there are certain provisions in most technical conditions of powder metallurgy. For example, the powder may have an oxygen content of 0.2% to 1.5%, which corresponds to an oxide content of 1% to 10%.

Powder metallurgy related enterprises are mainly used in the automotive industry, equipment manufacturing, metal industry, aerospace, military industry, instrumentation, hardware tools, electronic appliances and other fields of spare parts production and research, related raw materials, auxiliary materials production, various types of powder Preparation equipment, sintering equipment manufacturing. Products include bearings, gears, carbide tools, molds, friction products and more. Among the military enterprises, heavy-duty weapons and equipment such as armor-piercing projectiles, torpedoes, etc., and aircraft and tank brakes are all required to be produced by powder metallurgy. Powder metallurgy auto parts have become the largest market for China’s powder metallurgy industry in recent years, and about 50% of auto parts are powder metallurgy parts.

(1) Applications: (automobiles, motorcycles, textile machinery, industrial sewing machines, power tools, hardware tools, electrical appliances, engineering machinery, etc.) various powder metallurgy (iron based or copper based) parts.

(2) Classification: powder metallurgy porous materials, powder metallurgy friction reducing materials, powder metallurgy friction materials, powder metallurgy structural parts, powder metallurgy mold materials, and powder metallurgy electromagnetic materials and powder metallurgy high temperature materials, etc.