Research On Regulation Mechanism Of Thermal Conductivity Of Indium-based Liquid Metal/Diamond Composites

The growing“thermal barrier”problem of electronic devices brings new challenges to advance electronic packaging thermal management materials.For the application of phase change materials in the field of thermal management,liquid metal(LM)is considered as the most potential phase change material due to its low interfacial thermal resistance and high thermal conductivity.However,the thermal conductivity of LM still has a large room for improvement,and the leakage and supercooling of LM also need to be solved.Based on it,this work selected the In-based LM with better interface adaptability and diamond particles with high thermal conductivity.In-based LM/diamond composites were manufactured using powder sintering technology.The microstructures,components and thermal property of the composites were analyzed.Combining numerical simulation methods to study thermal conduction,wetting and phase transition behavior as well as the mechanism of the composite.In-based LM powder was prepared by high speed liquid phase dispersion method,which was used to fabricate the In-based LM/diamond composites.By adjusting and analyzing the morphology and particle size range of In-based LM powder,the optimal dispersing solution obtained was glycerol solution containing 5?10 vol%polyethylene glycol and 0.1?0.2 wt%citric acid;the optimal technological parameters were as follows:pre-heating temperature was 30?60?above the melting point of LM,dispersing time was 3?5 min and the dispersing rate was 1.2×10⁴?1.9×10⁴ rpm.Large-mass(?30 g)of LM powder can be prepared in a single process within a short time(3?5 min).The powder had high sphericity and good surface morphology,and the powder size mainly concentrated on 15?25?m.The liquid phase dispersion had no significant effect on the elemental distribution of LM particles and had little effect on their melting point.Combined with X-ray energy spectrum analysis,X-ray photoelectron spectrum analysis and in-situ observation experiments,it is verified that the surface of LM particles was an oxide film,which keeps the core-shell structure above their melting point.The shell can be removed by external force or chemical reagent.By analyzing the mechanism of LM powder prepared by liquid dispersed method,in order to obtain LM powders with narrow size range and high sphericity,under the premise of reasonable process parameters,the dispersion solution with low affinity for LM and trace deoxidized film reagent are preferred,so that the dispersed LM particles can form high sphericity powder depending on their own surface tension.Bi-In-Sn/diamond composites were successfully prepared by powder sintering technology.The results show that the Ti or Cr-coated diamond particles improved the interface bonding between Bi-In-Sn matrix and diamond.The thermal conductivity of Bi-In-Sn/diamond composites increased with the increase of diamond volume fraction and diamond size,and the relatively high thermal conductivity obtained was 71 W·m^-1·K^-1,which was 3.8 times higher than that of the matrix.The melting point of the composite was close to that of the matrix,and the volumetric latent heat of the composites decreased with the increase of diamond volume fraction.When the volume fraction of the diamond was the same as that of Bi-In-Sn,the contribution of sensible heat of the diamond to the volumetric latent heat of the Bi-In-Sn/diamond composites was 12%.After aging at 125?for 120 h,the melting point of the composite did not change significantly.However,the thermal conductivity of the composites decreased 5.5%,which was due to the oxidation of Bi-In-Sn.Combining numerical simulation results,the internal thermal transfer mechanism of Bi-In-Sn/diamond composites is as follows:heat flow is mainly transferred through adjacent diamond particles,which will enhance the thermal conductivity of the composites;over-thick carbide coating of diamond will significantly decrease the thermal conductance between diamond and LM,which will result in decreasing thermal conductivity of the composites.Voids in composites exist between diamond particles in the same direction as the heat transfer,especially at the interface between the matrix and the diamond,which will cause great changes in heat flux and its transfer direction.This will significantly reduce the thermal conductivity of the composites.Wetting behavior between diamond particles and different LM was analyzed using in-suit imaging and particle dipping experiment.The wettability of diamond particles with pure molten In was good,but the wettability of diamond with pure Ga was poor.The wettability of LM and diamond can be improved by alloying with In.The oxidation film on the surface of LM would hinder its wetting on the diamond surface.According to the calculation and analysis using density functional theory,the main reason for the good wettability of diamond with In was that the interface adsorption energy of In and diamond was relatively low.By taking advantage of the good wettability of diamond with In,an effective micro connection can be formed between In-based LM and diamond particles by pre-adding In particles.The thermal conductivity of In-based LM would be enhanced.In-based LM/diamond composites have good thermal stability after aging test.The highest thermal conductivity of the obtained Bi-In-Sn/diamond composites and In/diamond composites could reach 157 W·m^-1·K^-1 and 211 W·m^-1·K^-1.The thermal resistance between In and diamond was 0.2×10^-6 m²·K·W^-1 through differential effective medium model.In addition,a relatively reliable model for predicting the thermal conductivity of ternary composite materials was established,and the experimental value can reach more than 90%of the predicted value.The melting/solidification transformation behavior of Bi-In-Sn before and after the addition of diamond particles was analyzed.The initial melting time of Bi-In-Sn was delayed and the melting phase transformation lasted longer after the addition of diamond particles.When the heating element worked for a long time,Bi-In-Sn/diamond showed better heat dissipation ability than Bi-In-Sn.The solidification time of Bi-In-Sn was advanced and the degree of supercooling decreased after diamond particles were added.For the intermittent heating element,the solidification process of Bi-In-Sn was relatively shortened after diamond particles were added,and it showed good thermal stability after cycle tests.Through 1000 melting/solidification cycle tests of Bi-In-Sn/diamond,it was found that the relative position of diamond particles in Bi-In-Sn was basically stable.Combining simulation analysis,the influence mechanism of diamond on LM phase transformation process is as follows:the addition of diamond particles can enhance the local thermal conductance of LM,which would balance the internal temperature of LM and result in the heat not being easy to accumulate in the internal LM.That would delay the melting phase transition of LM and LM would maintain high thermal conductivity.During the cooling process,diamond particles accelerated the internal temperature transfer of LM,so that the overall solidification phase transition was more uniform and the solidification time was relatively shortened.