In recent years, with the continuous development and progress of science and technology, traditional materials have been unable to meet the performance requirements of many industries, such as specific strength and specific stiffness. Research and development of high-performance materials is an important direction of the development of new science and technology, and the emergence of composite materials to a large extent solved the problems faced by materials and promoted the development of materials. Composite material is composed of two or more kinds of materials with different properties through physical or chemical methods in macro (micro) with new properties. Due to its high specific strength and specific stiffness, the research and development of metal matrix composites have been paid close attention by many industries, especially the heavy industry. However, the processing difficulty is the bottleneck problem limiting its industrial application, and the cost control problem has not been completely solved, so it is more applied in aerospace, military science and technology and other cutting-edge scientific and technological fields.
In recent years, people have developed a variety of effective methods to prepare metal matrix composites by studying the law of interfacial reaction between metal matrix and reinforcement and the methods of controlling the interface reaction, which greatly promotes the development and application of metal matrix composites. At present, the preparation methods of metal matrix composites can be divided into two types: the second phase external addition method and the in-situ composite method.
The second phase addition method is a method of adding reinforcement into the matrix to prepare composite materials, which is widely used. The common second phase addition methods include powder metallurgy, casting solidification and spray forming.
1. Powder metallurgy
The preparation of composite materials by powder metallurgy means that the metal matrix and reinforcement powder are mixed evenly and then pressed, sintered at a temperature lower than the liquidus of metal, and the metal matrix is combined with the reinforcement powder by atomic diffusion. The preparation of composites by powder metallurgy generally includes four steps: screening powder, mixing matrix powder with reinforced particles, powder pre pressing, hot pressing and secondary processing. The common secondary processing methods of powder metallurgy are extrusion, rolling and so on. The secondary processing can realize the densification treatment of parts and achieve the final forming purpose. The advantages are: the matrix metal composition and the type and size of strengthening particles can be freely selected; the matrix metal is not easy to react with the strengthening particles due to the low composite temperature, so as to give full play to the characteristics of various raw materials; the particles are uniformly strengthened, and the range of reinforcement particles is large, and multiple particles can be strengthened together.
Figure 1. SPS sintering furnace (left) and vacuum sintering furnace (right) produced by our company
2. Casting solidification molding method
Casting solidification molding method is to heat the matrix metal to the molten state, and then make it composite with the reinforced phase to obtain metal matrix composite. The metal matrix composites prepared by casting solidification molding method have the advantages of low cost, simple process and easy control. The products obtained are of good quality and are widely used. The common methods are stirring casting and squeeze casting. Stirring casting is a common method to prepare metal matrix composites. It mixes the molten metal matrix and reinforced phase by mechanical stirring to prepare composite materials. Due to its low cost and simple process flow, stir casting method has been widely concerned. Its equipment investment is less, and the secondary processing of parts as the pretreatment process of superplastic deformation can further improve its performance. The stirring casting method can be used to produce large volume parts, which is convenient for large-scale production. There are a lot of application examples in the aerospace field of high-end science and technology, or in the automotive, mechanical industry and other civil fields. Squeeze casting is an accurate casting method which uses high pressure to make liquid metal or semi-solid metal filled and solidified. The preparation of metal matrix composites by liquid die forging is that the reinforced phase is pre formed, heated and poured into liquid metal or melt, and then the die is pressed and cooled to obtain metal matrix composite parts.
Figure 2. Parts produced by casting
3. Spray molding
Spray forming is a new type of metal forming technology. The molten metal is atomized and sprayed by rapid solidification technology. After deposition, the metal blank is directly obtained, which is also called spray deposition. Spray forming was introduced to prepare composite materials in the 1980s, and it has been developed rapidly because of its universal adaptability. The preparation of metal matrix composites by spray forming technology is to spray the molten metal with rare gas, and then mix it with the reinforced phase transported by rare gas at the other end, and deposit on the water-cooled substrate platform to form composite parts.
In situ composite, also known as reactive synthesis technology, is a new method to prepare metal matrix composites. Different from some traditional methods, the in-situ composite method does not need additional reinforcement phase, but uses some special reaction to make the reinforcement phase self-formed in the metal matrix, thus avoiding the phenomenon of reinforcement phase segregation in the composite material. In the process of preparing composite materials by in-situ composite method, the reinforced phase can be solidified and precipitated in the form of eutectic, and the composite material is called directional solidification eutectic composite; it can also be obtained by the reaction of corresponding elements and added elements in metal matrix and alloy melt, which is called self-formed composite material. Because the nucleation and growth of the reinforced phase are completed in the matrix, there is no physical and chemical incompatibility between the reinforcement phase and the matrix. The wetting effect is good and the bonding strength is high. There is no need to pretreat the reinforced phase to ensure its purity.
Fig. 3. Schematic diagram of metal organic framework material prepared by in situ composite method
At present, more and more preparation methods of metal matrix composites are being developed. In addition to several common methods mentioned in this paper, there are also many kinds of composite methods, such as immersion solidification, hot dip and reverse solidification, laminated composite method and so on. With further research, it is believed that more preparation methods of composite materials will come out, which will promote the popularization and development of metal matrix composites. Compared with traditional metal or alloy materials, the manufacturing cost of metal matrix composites is higher and the process is more complex. For civil industrial enterprises, the high production and research cost is the biggest problem restricting the large-scale application and production of metal matrix composites. Therefore, in order to realize industrialization and large-scale production, it is necessary to further study the preparation methods and develop new preparation processes, so as to reduce the cost and enhance the competitiveness of metal matrix composites in the material market.
According to the market demand, Haoyue technology continuously develops and improves technology, introduces heat treatment equipment with excellent performance, and provides corresponding technical support to assist domestic composite market and provide corresponding technical consultation for heat treatment process of composite material industry.
Haoyue echnology is a high-tech enterprise integrating R & D, production and sales of electric furnace. The company has been focusing on advanced ceramics and composite materials, semiconductor materials, carbon materials, lithium batteries and new energy materials equipment four major fields, has rich industry experience and professional technology, wholeheartedly serves customers and provides perfect integrated industrial solutions.