Metal matrix composites

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Metal Matrix composites (MMCs) are mainly composed of Metal and alloy as Matrix materials and fiber, whisker, particle and other high-strength materials as reinforcement.

The commonly used preparation methods of MMCs include powder metallurgy, in situ generation complex method, jet forming method, casting solidification forming method, etc. According to the different reinforced phase can be divided into continuous fiber reinforced (mainly carbon and graphite fiber, silicon carbide fiber, boron fiber, alumina fiber, stainless steel wire and tungsten), of continuous fiber reinforced (such as silicon carbide, alumina, boron carbide particle, silicon carbide, alumina, whisker reinforced, such as alumina fiber such as short fiber reinforced) and three types of laminated composite composite materials.

Because of the introduction of reinforced phase in a certain extent can change the microstructure of substrate material and organization, such as the structure, dislocation configuration and the grain size and so on, so as to improve and make up for the defects of the substrate material on some performance than the MMCs has high specific strength and modulus, high temperature resistance, corrosion resistance, small thermal expansion coefficient, dimensional stability, good electrical and thermal conductivity and other excellent physical and mechanical properties. Therefore, MMCs has replaced some traditional materials and gradually become the key field of material science research at home and abroad.

Copper is one of the earliest and most practical metals discovered by human beings. Due to its excellent ductility, it is second only to silver in electrical conductivity and second only to gold and silver in thermal conductivity, which has attracted much attention for a long time. However, the poor mechanical properties of copper (wear resistance, hardness, strength, creep resistance, etc.) limit its application in industrial and military fields. In many MMCs, copper-based composites are widely concerned for their excellent electrical and thermal conductivity, corrosion resistance and good processing property. Since the 1960s, the research on copper matrix composites has been carried out gradually. Many scientists have added different reinforcers to the copper matrix, and found that the composites not only maintain the advantages of copper, but also make up the deficiency in the mechanical properties of copper. Up to now, the research on copper matrix composites has been going on for several decades, forming three categories: particle reinforced copper matrix composites, fiber reinforced copper matrix composites, and whisker reinforced copper matrix composites.

Particle – reinforced copper – based composites

The purpose of particle reinforced copper matrix composites is to disperse the excellent particles in copper matrix and improve the comprehensive properties of copper matrix composites. The pinning effect produced by the particle reinforcing phase can greatly hinder the dislocation movement, thus enhancing the strength of the composite material, and greatly improving the mechanical properties, abrasion resistance and high-temperature properties of the copper matrix composite material. In addition, due to the small amount of particle reinforcement, the original physical and chemical properties of the matrix material are not affected, so the original high electrical conductivity and thermal conductivity of the matrix material are not significantly reduced. The common particle reinforcing phases are Al2O3, WC, TiB2, Ti3SiC2, etc. At present, the most studied is Al2O3. Due to the high mechanical properties of Al2O3 enhanced copper matrix composite, its electrical conductivity and thermal conductivity are close to pure copper, as well as its good corrosion resistance and wear resistance, the composite has entered the practical stage. WC particles are characterized by high strength, high hardness, high melting point and high elasticity, so WC enhanced copper matrix composites also have high strength, high hardness and high conductivity, heat conduction and other characteristics. TiB2 particles are characterized by excellent stiffness, high hardness and good wear resistance, so TiB2 enhanced copper matrix composites have excellent stiffness, hardness and wear resistance. Ti3SiC2 is a new type of material with excellent structure, conductive and self-lubricating properties. It has the same characteristics of conducting, conducting and easy to be processed as metal materials. At the same time, it also has the characteristics of light weight, oxidation resistance and high temperature resistance of ceramic materials. Therefore, Ti3SiC2 reinforced copper matrix composite is an excellent self-lubricating material, and its mechanical properties are better than SiC reinforced copper matrix composite.
Due to the comprehensive performance of both metal and nonmetal (strong toughness, wear resistance, heat resistance, conductive thermal conductivity and weatherability), particulate reinforced copper matrix composites can be widely used engineering requirement, and its than strength, modulus and high temperature stability than base material, the development of cutting-edge domains such as aerospace plays an important role.

Fiber reinforced copper matrix composites

Fiber-reinforced copper matrix composites (FIBER-reinforced copper matrix composites) are a method of reinforcing copper matrix with extremely strong metal wires or fibers (diameter 3~5 m), and are also the earliest strengthening methods applied to copper matrix composites. Due to the fiber reinforced phase has good high temperature resistance, excellent conductivity, heat conduction, fatigue resistance, and excellent dimensional stability in radiation and humid environment, fiber reinforced copper matrix composites are considered to have a great application prospect in aerospace, automobile, electronics and other fields due to their high strength and high temperature resistance. The properties of fiber-reinforced copper matrix composites are determined by the properties of the fibers, which require that the fiber-reinforced copper matrix composites have high aspect ratio, high specific strength, high specific modulus, stable high-temperature oxidation resistance and good conductivity and thermal conductivity. At present, there should be a wide range of fiber reinforcement mainly include: B fiber, C fiber, SiC fiber and Al2O3 fiber. B fiber is characterized by low density, high aspect ratio, high elastic modulus, high thermal conductivity, excellent thermal stability, etc. Compared with B fiber, C fiber has low density, excellent mechanical properties, good lubrication and wear resistance, and its manufacturing cost is lower. Compared with B and C fibers, SiC fibers have higher mechanical properties, better high-temperature properties and stronger oxidation resistance under high temperature conditions. Therefore, SiC fiber is mainly used in the manufacture of various high-temperature resistant and high-performance structural parts of aircraft, missiles and engines.

Whisker reinforced copper matrix composite

Whisker – reinforced copper – based composites are mainly beneficial to a method of whisker – reinforced copper – based composites. The fine needle-like crystals without defects (i.e. there is only one spiral dislocation on the growth axis) are called whiskers. Generally, the length-diameter ratio is greater than 10, and the cross-sectional area is less than 52×10-5 cm-2. Now, short fibrous crystals are also considered as a type of whisker. Crystallization, whisker has arranged highly ordered atomic structure, the characteristics of few internal defects, so the strength and modulus of whisker are close to full theoretical calculation value of grain boundary material, so that the whisker reinforced phase become a kind of excellent mechanical properties of enhanced toughening, can significantly improve the corrosion resistance of abrasion resistance and thermal fatigue resistance, and can effectively reduce the expansion coefficient of material. Therefore, the synthesis and application of whisker has become a hot research field in material science. After years of research and development, a total of more than 100 whisker types have been formed, mainly consisting of SiC, Si3N4, K2Ti6O13, Mg2B2O5, Al18B4O13, Al2O3 and ZnO. Among all whiskers, SiC whiskers are known as “the king of whiskers” and are the key field of research and application. SiC whiskers have the highest properties of strength, elastic modulus, tensile strength and heat resistance of all synthesized whiskers. Similar to SiC, Si3N4 whisker has slightly lower hardness but better machining performance. The late development of K2Ti6O13, Al18B4O13, Mg2B2O5 whiskers in addition to excellent performance but also cheaper.

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