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What is the use of powder metallurgy?
Abstract: What is powder metallurgy? Powder metallurgy is a process technology that takes metal or metal powder (or the mixture of metal powder and nonmetal powder) as raw materials and makes metal materials, composite materials and various products through molding and sintering. Methods of powder metallurgy What is the purpose of powder metallurgy?

Powder metallurgy is a technology to make metal or metal powder (or the mixture of metal powder and non-metal powder) into metal data, composite data and various finished products after molding and sintering. Powder metallurgy is similar to the production of ceramics, so a series of new powder metallurgy technologies can also be used to prepare ceramic materials. Due to the advantages of powder metallurgy technology, it has become the key to deal with the problem of new materials and plays a decisive role in the development of new materials.

Powder metallurgy has the same chemical composition and mechanical and physical functions, which can not be obtained by traditional casting methods. Porous, semi-fine or full-fine materials and finished products, such as oil-bearing bearings, gears, cams, guide rods and cutters, can be directly manufactured by using powder metallurgy skills. This is a small cutting skill.

Powder metallurgy application

1. Powder metallurgy technology can minimize segregation of alloy components and eliminate rough and uneven forging arrangement. It is mainly used to prepare high-functional rare earth permanent magnet data, rare earth hydrogen storage data, rare earth luminescence data, rare earth catalysts, high-temperature superconducting data, new metal data such as Al-Li alloy, heat-resistant aluminum alloy, super alloys, powder corrosion-resistant stainless steel, powder high-speed steel, high-temperature structure data of intermetallic compounds, etc.

2. It can prepare a series of high-functional non-equilibrium data, such as amorphous, microcrystalline, quasicrystalline, nanocrystalline, super-full solid solution and so on, and has excellent electrical, magnetic, optical and mechanical functions.

3. It is a skill to produce high-functional metal matrix and ceramic composite materials at low cost, which can easily complete various types of composite materials and give full play to the respective characteristics of each component data.

4. It can produce materials and finished products with special structures and functions that can not be produced by ordinary smelting methods, such as new porous biomaterials, porous separation membrane materials, ceramic abrasives with high functional structures, functional ceramic materials, etc.

5. Near-net molding and automatic mass production can be completed, and further, production funds and energy consumption can be effectively reduced.

6. Being able to make full use of ore, tailings, steel-making sludge, steel-rolling scale and recycled scrap metal as materials is a new skill that can be used for data regeneration and comprehensive utilization.

Powder metallurgy method

(1) to produce powder. The production process of powder includes powder preparation and powder mixing steps. In order to improve the formability and plasticity of powder, plasticizers such as engine oil, rubber or paraffin wax are usually added.

(2) press molding. The powder is pressed into the required shape under the pressure of 15-600MPa.

(3) sintering. In a high temperature furnace or a vacuum furnace with a protective atmosphere. Sintering is different from metal melting. At least one element is still in a solid state during sintering. In the sintering process, powder particles become metallurgical products with certain porosity through a series of physical and chemical processes such as diffusion, recrystallization, welding, bonding and dissolution.

(4) Post-treatment. Generally speaking, sintered parts can be used directly. However, for some parts with high dimensional accuracy, high hardness and good wear resistance, post-sintering treatment is needed. Post-treatment includes fine pressing, rolling, extrusion, quenching, surface quenching, oil immersion and infiltration.

Preparation method of powder

Powder preparation is the first step of powder metallurgy. There are more and more powder metallurgy materials and products, and the quality is getting higher and higher, so the requirements for powder varieties are getting higher and higher. For example, from the range of materials, not only metal powder, but also alloy powder, metal compound powder and so on are used; From the appearance of powder, it is required to use various shapes of powder, such as molding powder when producing filters; From the point of view of powder particle size, powders with various particle sizes are needed, such as coarse powder of 500~ 1000 micron, ultrafine powder below 0.5 micron and so on.

In order to meet the requirements of powder, there are various methods to produce powder. These methods are nothing more than changing metals, alloys or metal compounds into powder in solid, liquid or gaseous state. Various methods for preparing powder and powder prepared by various methods.

The method for converting metals and alloys or metal compounds into solid powder comprises:

(1) There are two methods to prepare metal and alloy powder from solid metal and alloy: mechanical crushing method and electrochemical corrosion method;

(2) Reduction method for preparing metal and alloy powder from solid metal oxide and salt-chemical method for preparing metal compound powder from metal and alloy powder, metal oxide and nonmetal powder.

The method for convert metals and alloy or metal compounds into liquid powder comprises:

(1) There is an atomization method for preparing alloy powder from liquid metal and alloy.

(2) The methods of preparing metal alloy and coated powder by replacement and reduction from metal salt solution include replacement method and solution hydrogen reduction method; There is a molten salt aging method to prepare metal powder by precipitation from molten metal; Metal bath method is a method to prepare metal compound powder by auxiliary metal bath precipitation.

(3) electrolyzing metal and alloy powder from the metal salt solution; There is a molten salt electrolysis method to prepare metal and metal compound powder from metal molten salt electrolysis.

A method for converting metal or metal compound into gaseous powder:

(1) vapor condensation method is used to prepare metal powder by vapor condensation of metal;

(2) Carbon-based pyrolysis method for preparing metal, alloy and coating powder from gaseous metal carbon-based materials.

(3) gas-phase hydrogen reduction method for preparing metal and alloy powder and metal and alloy coating from gas-phase metal halide; There is a chemical vapor deposition method for preparing metal compound powders and coatings from gaseous metal halide deposition.

But from the essence of the process, the existing milling methods can be roughly divided into two categories, namely, mechanical methods and physical and chemical methods. Mechanical method is a technological process in which raw materials are mechanically crushed and the chemical composition is basically unchanged; Physical chemistry method is a process of changing the chemical composition or aggregation state of raw materials by means of chemical or physical action, so as to obtain powder. There are many ways to produce powder. On the industrial scale, the most widely used Hans reduction method, atomization method and electrolysis method are also very important in special applications, such as vapor deposition method and liquid deposition method.

The basic process of powder metallurgy is:

1, preparation of raw material powder. The existing milling methods can be roughly divided into two categories: mechanical method and physical and chemical method. Mechanical methods can be divided into: mechanical crushing and atomization; Physical and chemical methods are divided into electrochemical corrosion method, reduction method, chemical method, reduction-chemical method, vapor deposition method, liquid deposition method and electrolysis method. Among them, reduction method, atomization method and electrolysis method are the most widely used.

2. The powder is molded into a blank with a desired shape. The purpose of molding is to make a compact with a certain shape and size, so that it has a certain density and strength. Forming methods are basically divided into pressure forming and pressureless forming. Compression molding is the most widely used in pressure molding. In addition, 3D printing technology can be used to make blanks.

3. Sintering of green body. Sintering is a key process in powder metallurgy. The formed compact is sintered to obtain the required final physical and mechanical properties. Sintering is divided into unit sintering and multi-system sintering. For solid state sintering of unit system and multi-component system, the sintering temperature is lower than the melting point of the metal and alloy used; For multi-component liquid phase sintering, the sintering temperature is generally lower than the melting point of refractory components and higher than the melting point of fusible components. In addition to ordinary sintering, there are special sintering processes such as loose sintering, impregnation and hot pressing.

4. Post-processing of products. The treatment after sintering can be carried out in various ways according to different product requirements. Such as finishing, oil immersion, machining, heat treatment and electroplating. In addition, in recent years, some new technologies, such as rolling and forging, have also been applied to the processing of powder metallurgy materials after sintering, and satisfactory results have been achieved.

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