In recent years, ultrafine powder, especially nano-scale ultrafine powder with its peculiar small size effect, surface and interface effect, quantum size effect has been paid more and more attention, at the same time, people through experimental research, found that 2 or more than 2 kinds of powder particlessurface coatingorcompound treatmentAfter that, high-performance composite materials can be obtained, often in addition to the performance of a single powder, but also has a composite synergistic multi-function, change the surface properties of a single particle, increase the contact area of two or more components and so on.

Among themMetal-ceramic composite powderIt refers to the composite ceramic powder formed by coating a layer of metal on the surface of ceramic particles, which has the properties of metal coating and ceramic core core, and can achieve uniform mixing between individual particles. The sintered body or composite material has the following characteristics:(1) to improve the interfacial bonding force between powder ceramic and metal, and to improve the uniformity of ceramic and metal distribution in the sintered body;(2) to achieve multi-level and multi-mechanism composite reinforcement (fine grain reinforcement, phase transformation reinforcement, fiber reinforcement, etc.) to prepare metal composite ceramics with high strength and toughness level;(3) Low-density functional powder materials (such as low-density conductive powder, magnetic powder, etc.) can be prepared.

Commonly used metal-ceramic composite powders are composed of oxides (such as Al₂O₃、ZrO₂、 SiO₂), carbide (such as WC, TiC, SiC), etc. and metal composition, because of its excellent composite properties, can meet the special requirements of many fields, in recent years has become a hot spot in the study of composite materials.

Metal-ceramic composite powders are generally prepared by metal cladding technology in industry, and the preparation methods are usually as follows:Mechanical mixing, high-energy ball milling, self-propagating high-temperature synthesis, in-situ reaction, sol-Gel, chemical platingWait.

Mechanical mixing method is the earliest method used in the preparation of composite powder, the technology is simple to operate, simple process, has a complete set of equipment for industrial production, large output, low cost, so some composite powder preparation is still using mechanical mixing method. However, due to the different particle size and surface characteristics of the powder, the doping component is easy to segregate, easily lead to uneven composition and tissue, the resulting powder particle size is large, it is difficult to obtain the uniform distribution of the reinforcement particles, not suitable for the preparation of composite powder with high functional requirements.

The mechanical mixing method is widely used in the preparation of ZnO pressure sensitive composite porcelain powder in China.

High-energy ball milling method is a new progress in the study of mechanical alloy technology, it will be more than two kinds of metal or non-metal powder mixture, through high-energy ball milling, finally formed with a microstructure of alloy or composite ceramic powder. Compared with the traditional mechanical mixing method, it has the advantages of significantly reducing the reaction activation energy, improving the uniformity of particle distribution and the interface bonding between the reinforcement and the matrix. However, the preparation of composite ceramic powder by high-energy ball milling is a complex material reaction and structure control process, which has many influencing factors and strict process requirements.

Self-propagating high-temperature synthesis (SHS) is to ignite powder compacts in a certain atmosphere to produce chemical reactions. The generated heat released by the reaction causes the temperature to rise suddenly and triggers new chemical reactions of adjacent materials. The chemical reactions spread through the whole reactant in the form of combustion waves, and the reactants are converted into products when the combustion waves move forward. Self-propagating high-temperature synthesis technology has many advantages: simple production process, low investment, full use of energy, rapid response (0.1~15 cm/s). The synthesis reaction temperature is generally very high, which can volatilize most impurities to obtain high purity products.

The main disadvantage of SHS method is that it can not strictly control the reaction process and product performance, and it is not easy to obtain high-density products. In addition, the raw materials used in SHS method are often flammable, explosive or toxic substances, which need to take special safety measures.

Sol-gel technology (Sol-Gel) technology is a new process for the preparation of glass, ceramics and other inorganic materials developed in the 1960 s. In recent years, many people use this method to prepare nano materials, its basic principle is the use of metal alkoxide or inorganic salt hydrolysis to form a sol, and then make it into a gel, by drying, burning prepared nanoparticles.

This method process is more complex, the price of raw materials is more expensive, some raw materials are organic, harmful to health; secondly, usually the whole sol-gel process takes a long time, and there are a large number of micropores in the gel, in the drying process will escape a lot of gas and organic matter, and produce shrinkage, loss, high preparation cost.

Electroless plating is an advanced method for the preparation of metal-ceramic composite powders. This method can obtain uniform metal coating on the surface of various powder materials such as glass, ceramics, plastics or metal surfaces, and its reaction mechanism is based on the controlled autocatalytic redox reaction in solution. Therefore, it has attracted wide attention as a new method for the preparation of metal composite powders. It is found that the metal-ceramic composite prepared by electroless plating has higher toughness, better dispersion and more uniform surface coating.

At present, some domestic enterprises can mass-produce metal-composite ceramic powder, the products are mainly metal Ni, Co, Cu, Ag and other coated Al.₂O3、TiC、SnO₂、 SiO₂、CeO₂Such as metal ceramic composite powder, coated metal content from 5 to 90%. Product applications include ceramic cutting tools, electrical contacts, conductive pastes, rubber fillers, and automotive parts manufacturing materials.

Foreign enterprises of the same kind mainly produce Ag-coated SiO.₂Powder for stealth, electrostatic shielding coating, Cu, Fe and other coated SiC, graphite for particle reinforced metal matrix composite materials, Au, Ni coated polymer and ceramic powder for conductive paste, most manufacturers use chemical plating technology.

Metal-composite ceramic powder has great potential, its application is far more than the existing products on the market, widely used in military, aviation, aerospace, chemical, pharmaceutical and other fields.

（1) Metal toughened ceramic materials

Metal-ceramic composite powder is sintered (including pressureless sintering, hot pressing sintering, hot isostatic pressing sintering, etc.) to prepare high-performance cermets. Compared with single ceramic powder sintering, it has the following characteristics: the sintering temperature is greatly reduced, the molten or semi-molten metal phase is evenly distributed among the ceramic particles, which inhibits the growth of ceramic grains and prevents the generation of gas phase or glass phase. The metal phase in the sintered body is continuously distributed, and the ceramic particles are interlaced, which improves the bonding state of the ceramic phase interface, improves the bonding strength of the interface, and can give full play to the plasticity and toughness of the metal, and improves the stress state of the sintered body under load, thus effectively improving the strength and fracture toughness of the metal ceramic sintered body.

（2) Ceramic particle reinforced metal matrix composites

The high hardness of wear-resistant ceramic particles and metal materials composite, the high hardness of ceramic particles, high wear resistance with the toughness of the metal matrix material combined, in the wear-resistant parts of the working surface to form a certain thickness of the ceramic metal composite layer, the composite layer to withstand wear, the metal matrix plays a bearing role. This local composite way can not only improve the wear resistance of wear parts, but also ensure its overall toughness.

The particles commonly used in the preparation of particle reinforced metal matrix composites are WC, TiC, Al₂O₃ZTA (Zirconia Toughened Alumina) ceramic particles. Among them, ZTA ceramic particles have great advantages in hardness, toughness and cost, and have been widely used in ceramic-metal composite square hammer, plate hammer, hammer, grinding roller and other products.

(3) Thermal spraying powder

Thermal spraying materials are mainly used for corrosion, oxidation and wear protection of high-temperature components, but a single ceramic coating has many pores, poor fracture toughness, and a large difference in thermal expansion coefficient with the metal substrate material, its application is greatly limited. Therefore, in recent years, the use of metal-ceramic composite powder as a spray material for thermal spraying technology has been widely concerned.

(4) Special functional materials

The surface modification of SiC and hollow glass microspheres by electroless nickel plating can realize the micro layer composite of materials, improve the absorbing ability of SiC itself, and make the hollow glass microspheres have good absorbing properties. The noble metal is plated on the sub-micron and nano-scale inorganic particles, and the whole composite powder has special optical and electrical properties due to the nano-size structure of the noble metal particles adsorbed on the surface of the substrate.

At present, the most widely used is still used to prepare cermets. For example, in the aerospace field, many parts of the aircraft need to use materials with high temperature resistance, wear resistance and high strength, which have been gradually replaced by cermets. Cutting tools made of cermets are also very popular in the field of processing and manufacturing. For example, compared with ordinary refractory materials, cermets have higher thermal shock resistance and can be used for high-temperature equipment components.

Source:

Preparation, Mechanism and Application of Metal-ceramic Composite Powders, Zhu Liu (Zhejiang University);

Powder ring;