Microstructure And Thermo-physical Properties Of Diamond Particles Reinforced Composites For Radiating Substrate

With booming electronic industry and growing requirement for highly integrateddevices, traditional materials for radiating substrate have not fulfilled their performancerequirements. As is known to all that single crystal diamond has high thermal conductivityand low thermal expansion coefficient, so diamond composites have became hot spots inthe new material research field of radiating substrate. Diamond-Si and diamond-Cucomposites prepared by spark plasma sintering process have excellent thermo-physicalproperties in this work. The microstructures and properties of materials were analyzed byfield emission scanning electron microscope （FSEM）, EDAX-energy spectrometer, X-raydiffractometer （XRD） and testers of thermal conductivity and thermal expansioncoefficient.The research of diamond-silicon composites shows that increase of silicon contentreduced sintering temperatures and increased relative packing density obviously.Diamond-Si composites prepared by in-situ reactive spark plasma sintering yieldedexcellent thermo-physic properties and high relative density. As a result of reaction betweendiamond and silicon, SiC phase formed. This study shows that silicon facilitates reductionof porosity and hinders diamond graphitization. Thermal conductivity of samples sinteredimproved obviously with the increase of diamond content. Thermal conductivity andthermal expansion appear to be strongly related to interface microstructure, particularly tointerfacial bonding between the silicon matrix and the diamond particles. Samples sinteredin argon have remarkably high thermal conductivity and relative packing density comparedwith the samples sintered in vacuum. In the sample with trace aluminum, the Al phase isfound to be embedded in the interface between diamond and silicon. The addition ofaluminum improved relative density of samples sintered but reduced the thermalconductivity. The addition of titanium not only improved relative density of samples sintered but also increased the thermal conductivity. Compared with the use of low qualityFDP-diamond particles (thermal conductivity is about1000W·m^-1·K^-1), diamond-siliconcomposites have superior thermal physical properties via using high qualityMBD8-diamond particles (thermal conductivity is about2000W·m^-1·K^-1).The interfacial microstructures and thermal conductivities of Cu/diamond compositeswere examined. The results show that （Al or Si）-coated diamond particle is an effectiveapproach to promoting the relative packing density and improving thermal conductivity ofsamples sintered. Thermal conductivity of Al-coated diamond particles dispersed Cu-matrixcomposites containing40-50vol%diamond reached491-565W·m^-1·K^-1, higher than60%the theoretical thermal conductivity estimated by Maxwell-Eucken’s equation. Thecoefficient of thermal expansion of the Al-coated composites falls in the lines of Kernermodel and R-H model lower bound, indicating strong bonding between the Al-coateddiamond particles and the Cu-matrix in the composite. Thermal conductivity of Si-coateddiamond particles dispersed Cu-matrix composites containing40-50vol%diamond reached401-535W·m^-1·K^-1, higher than55%the theoretical thermal conductivity estimated byMaxwell-Eucken’s equation.On the basis of Maxwell-Eucken model and Hasselman-Johnson model, heatconduction theory of composite would be revised by considering relativity density.