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Preparation of diamond/aluminum composite materials

Metal matrix composites have great advantages in heat transfer performance due to their special structure. Among them, diamond/aluminum composite material has become a research hotspot and development direction in the field of thermal management due to its advantages of low density, high thermal conductivity and adjustable thermal expansion coefficient. For example, as a thermal management material with excellent thermal conductivity, it can coordinate gradually increasing power The temperature difference between the density and the surrounding environment achieves efficient heat dissipation and reduces the mismatch with the thermal expansion coefficient of the chip material, and improves the stability and reliability of the system.

The thermal conductivity of diamond/aluminum composite materials largely depends on the preparation process. Therefore, the composite process method is particularly important in material research. There are various preparation methods of metal matrix composites. With the advancement of process technology and equipment, more new methods and new processes are gradually derived. At present, the mainstream preparation methods of diamond/aluminum composite materials mainly include pressureless infiltration, vacuum pressure infiltration and squeeze casting, spark plasma sintering, vacuum hot pressing sintering, etc.

1. Pressureless infiltration
The pressureless infiltration preparation process was proposed by the American Lanxide Company in 1989 on the basis of the direct metal oxidation process. The main process is to first make the reinforcement powder into a preform through an adhesive or pre-sintering molding, and then the matrix The metal is placed on the upper or lower part of the reinforcement, heated under the protection of the atmosphere, so that the melting of the metal spontaneously penetrates into the gap of the preform, and finally it is cooled and solidified. The pressureless infiltration method can realize low-cost preparation of composite materials with large planar dimensions and complex surface shapes, and is suitable for mass production. However, the key to limiting the performance of the process is the problem of density. Therefore, the performance of composite materials prepared by pressureless infiltration is The preparation process parameters are very sensitive; at the same time, the higher preparation temperature also brings difficulty to the control of the interface reaction between the diamond and the aluminum matrix.

2. Vacuum pressure impregnation
Vacuum pressure infiltration is to put the preform in the mold, use vacuum to remove the gas in the preform, and then inject the inert gas into the smelting furnace at a certain pressure, squeeze the liquid metal into the cavity, and infiltrate the pores of the preform. Thereby a composite material blank is obtained. The process has no restrictions on the type, shape and alloy type of the reinforcing phase, and the net shape of the material can be realized through the mold design, and at the same time, it overcomes the insufficient and dense problems of pressureless infiltration and has fewer casting defects.

3. Squeeze casting
Squeeze casting is a method in which a liquid or semi-liquid metal matrix is impregnated into a preform containing a reinforcing phase by external pressure, and solidified and formed to obtain a composite material. This process has almost no restrictions on the shape and type of the reinforcing phase and the composition of the base alloy, and the composition design can be carried out in a wide range. Since the composite material is solidified and formed under high pressure, the requirements for alloy wettability are reduced, and the casting structure defects are also less.

4. Spark plasma sintering
Spark plasma sintering is also called “plasma activated sintering”. This technology originated from the “pulse sintering technology” introduced by the United States in the 1930s. Later, Japan developed more advanced electrical spark sintering on this basis, and obtained the corresponding Patent, but because of the low production efficiency of this technology, it has not been promoted and applied; until 1988, Japan first developed the first SPS equipment with a maximum sintering pressure of 5 tons, which was promoted in the field of new materials research. The process is sintered by direct current pulse current through metal and ceramic particles pre-loaded into the mold, so that each particle instantly generates Joule heat. It has uniform heating, high heating rate, low sintering temperature, short sintering time, and high production efficiency. The advantages. The density, structural defects (such as particle damage, impurities) and interface bonding state of the diamond/aluminum composite prepared by the SPS process are the key factors that affect its thermal conductivity.

5. Vacuum hot pressing sintering
Vacuum hot pressing sintering is a traditional powder metallurgy method for preparing metal matrix composites. The preparation process mainly includes screening, mixing, cold pressing, degassing, and hot pressing sintering of metal powder and ceramic particles, and then pressing to obtain aluminum Matrix composites. The composite material obtained by vacuum hot pressing sintering technology presents a micron-scale diffusion bonding interface, which is beneficial to the improvement of thermal conductivity.