Research On Interfacial Metallurgical Behavior Of Diamond/Metal And Thermal Properties Of Composites

Driven by the rapid development of electronics,it is critical to develop advanced thermal management materials for electronics packaging to ensure timely heat dissipation.Diamond/metal composites are considered as one of the most promising new thermal management materials.At present,the diamond/metal composites are often prepared by the infiltration method,while the interface problems are obvious in the interfacial metallurgical process of the composites prepared by the infiltration method,such as poor interfacial wettability,harmful interfacial metallurgical products and high interfacial thermal resistance.To solve these interface problems,W and Si preset layers were deposited on the diamond surfaces by magnetron sputtering in this thesis,and the infiltration process of the composite was determined via researching interfacial metallurgical behavior.The effects of interfacial metallurgical structures that are non-reactive and reactive liquid-solid interface on the thermal properties of the composites were systematically studied.The interfacial thermal conductance gain mechanism of the composite was revealed.This thesis provides data support and a theoretical basis for preparing the composite with high thermal conductivity and optimizing its interfacial structure.The W and Si preset layers prepared on the diamond surface by magnetron sputtering are uniform and compact.The different phases composition of the preset layers can be obtained by regulating the annealing temperatures.For the W layer,at900°C,the W layer begins to react with diamonds to form the W₂C phase.With the annealing temperature increasing to 1100°C,W and W₂C gradually transform into WC phase.To Si layers,they begin to crystallizing at 900°C.At 1300°C,they react with diamonds to form the SiC phase.To handle the serious evaporation of Si layers during forming the SiC phase at high temperature,a novel low-temperature method to coat the SiC on the diamond surface was proposed at low temperatures.The SiC layer has been synthesized by aluminum-silicon（Al-Si）mixed powders and vacuum annealing technology.We found the Si mass fraction in Al-Si powders and annealing temperatures have significant effects on the synthesis of the SiC layer at low temperature.When the Si mass fraction in Al-Si powders is 20-80 wt.%and the annealing temperature is not less than 750°C,the SiC layer can be successfully synthesized on the diamond surface.Synthesized SiC layer at low temperature is realized via gradual-reaction process,namely,diamond reacts with aluminum in aluminum-silicon powder to form Al₄C₃,and then Al₄C₃ reacts with Si to form SiC.The Al₄C₃ is an indispensable mesophase for low-temperature synthesizing SiC on the diamond surface.The W and Si preset layers on diamond plates were prepared by magnetron sputtering.The wettability,element diffusion behavior and interfacial metallurgical reaction of molten Cu（and Al）and preset layers were simulated in a sliding tube annealing furnace.Based on the interfacial metallurgical behavior,the infiltration process of the composites was determined.In diamond/Cu composites,the phase compositions of W preset layers have a significant effect on their metallurgical interface structure and thermal properties of the composites.The phase composition of the preset layer must be composed of tungsten carbides（W₂C and WC phase）for better interfacial bonding.With the interfacial phase transformed from metallic W to corresponding carbides,the thermal conductivity of the composites exhibited increasing firstly and decreasing subsequently,while its thermal expansion coefficient was opposite.When the metallurgical interfacial layer was composed of 97.6 wt.%WC phase and 2.4 wt.%W₂C phase（interface thickness of 395 nm）,the thermal conductivity of the composite reached to836 W·m^-1·K^-1,and the thermal expansion coefficient was 6.35×10^-6 K^-1.A small amount of W₂C phase existed in preset layer plays a positive role in further improving the thermal conductivity of the composites,and its thermal conductivity gain mechanism is that thermal boundary conductance of the W₂C/Cu interface is larger,and the W₂C/Cu combine with diamond/WC interface to enhance the overall interface thermal conductance of the composites.Meanwhile,the thin W₂C sublayer reduces the acoustic impedance mismatch between Cu and the interfacial layer,thus enhancing the thermal conductivity of the composites.Thermal properties of the composites can be further optimized by regulating the metallurgical interface thickness.When the thickness of WC layer is?240 nm,the thermal conductivity of the composite is 943W·m^-1·K^-1,and its thermal expansion coefficient is 5.57×10^-6 K^-1.The thickness of the WC interface layer changes affects its actual density,average phonon velocity and intrinsic thermal conductivity,further influencing the thermal boundary conductance of the two-phase interface.The essence of regulating interlayer thickness is to obtain maximum thermal boundary conductance,which is the key factor for the thermal conductivity gain mechanism of composites.In diamond/Al composites,the phase compositions of the W preset layers have a significant influence on metallurgical interface structure and thermal properties the composites.No matter what kind of phase composition existed in the preset layer before infiltration,it was scoured and reactive erosion by liquid Al during the infiltration process,resulting in the composites exhibiting different metallurgical interface structures.When the metallurgical interface structure is Diamond/WC/Al₄C₃/Al₅W/Al,the thermal conductivity of the composite can reach 658W·m^-1·K^-1,and the corresponding thermal expansion coefficient is 6.28×10^-6 K^-1.Compared with W preset layer,Si and SiC preset layers can retard the interfacial metallurgical reaction of diamond/Al composites,and obtain the metallurgical interfacial structures with better thermal properties and moisture resistance.The Diamond/SiC/Al₄C₃/Al interfacial structure can be obtained when the SiC preset layer is continuous and its thickness is more than 400 nm.The optimized thermal conductivity can reach 768 W·m^-1·K^-1 and the thermal expansion coefficient is 6.00×10^-6 K^-1.After soaking water for 680 h,thermal conductivity of the composite only decreased by 8.5%,showing good moisture resistance.In this interfacial structure,optimizing the thickness of the SiC layer and improving its quality（i.e.the intrinsic thermal conductivity）are the key factors to reinforce the heat transfer mechanism of diamond/Al composites.