| Diamond-reinforced metal matrix composites receive much attention and are considered to be a new electronic packaging materials due to their high thermal conductivity (TC), low coefficient of thermal expansion (CTE), good mechanical and surfaces property were proposed. And their preparation process became the focus of extensive research.In this paper, process and parameters during melt infiltration had been studied, and the densified mechanism had been also discussed. And then formulae and technology to prepare diamond/copper composites were proposed.The poor wettability between diamond and copper caused low interfacial bonding strength and the poor properties in the composites. The method such as molten salts bath was used to the surface modification of diamond particles by previous researchers. But the plating process was complex, inefficiency and unfavourable to the production and application of composites. Using an alloy was effective to improve wettability, shorten the preparation process, and to reduce the consumption of preparation. Molten metal infiltration is a low-cost andconvenient technology in the fabrication of metal matrix composites, including porouspreform preparation, alloying of matrix metal and controller of infiltrating.Properties and preparation of porous diamond preform and alloying metal matrix were researched, and infiltration process were discussed according to the properties of composites. Navier-Stokes equations of the infiltration were solved and simulated to describe the reaction-seepage coupled process, technology to prepare diamond/copper composites were proposed.A kind of thermoset phenol-formaldehyde resin (PF) was used as binder, contrasted with PVA. Porosity and strength of diamond preform were improved under the suitable amount and multi-pressure process. And then the debinding process of PF binder was discussed thoroughly. Under the PF amount of 15～20wt.% and the pressure of 40MPa, the strength of PF preforms reached to more than 4.5MPa, and the porosity was at the rate of 22-30%. The preform with 30～35% porosity was prepared after debinder process at the heated rate of 3℃/min. and an amorphous carbon layer was retained on the surface of diamond particles to promote the liquid copper alloy infiltrating into diamond preform by diffusion and carbide reaction. Porosity and strength of preform was improved by the addition of Cr or Mo powder under the particle size of 45 μm and the amount between 4.5～9wt.%.Alloying matrix prepared by powder metallurgy and pre-sintering process had better structures and performances than that prepared bytraditional method. Based on the density and thickness of carbide layer, theory amount of Cr should be at the ranges of 0.15～8.6wt.%. and that of Mo should be 0.13～9.2wt.%. Copper alloy was prepared from copper powder at the size of 30μm and Cr or Mo powder at 45μm, after the mould pressing process under 80MPa and pre-sintering at 1050℃ through 60-120min.The Navier-Stokes equations of molten metal infiltration was solved by Lattice Boltzmann method. The simulation results showed that molten copper alloy penetrated the porous preform through a 3-D reaction-flow coupling process, and the fluid-density of vertical penetration was less than its plane spread. So the vertical flow of liquid alloy decided the permeation process. Main elements of infiltration process were amount of carbon by PF, alloying component, infiltration pressure, temperature and time. Density of composites contained 15～20wt.% of PF or 4.5-9wt.% of Cr powder at 45μm was not less than 99%. Composite strength was high under the pressure of 40-50MPa through 30～60min. at 1075℃.Since the continued reaction of Cr in alloy and carbon by PF or diamond. Cr3C2 was the main resultant between diamond particles and copper matrix by Cr in alloy and carbon from PF and diamond along the the diamond surfaces. 15～20wt.% amount of PF improved carbonization efficiency and permeability., composite Density reached to over 99%. Better wettability between carbides and copper made the density reach to more than 99%. and its thermal and volumetric expansion of carbides provided impetus for capillary infiltration and microdefects were filled during the rapid densification of composites.Density related to the composite properties, such as TC, CTE strength, and surface roughness, Higher interfacial bonding strength made a higher composite strength and TC. But the thermal conductivity was reduced by the thermal resistance of excess carbide. Composites TC was more than 400 W·m-1K-1 and strength was up to over 300MPa when composites were prepared by 15-20wt.% of PF or 4.5-9wt.% of Cr powder at 45μm, under the pressure of 40-50MPa through 30-60min, at 1075℃. And the CTE of these composites was at the range between 5～10×10-6K-1 to meet the requirement of electronic packaging, contained. |
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