Study Of W-Cu Composite Coating Prepared By High Velocity Oxygen Fuel On Copper And Its Thermal Properties

With the increasing integration of integrated circuits and the everdecreasing of chip size,heat dissipation is the most critical and challenging problem.Although metal-based reinforced composite heat dissipation materials with thermal conductivity as high as 500 W/(m·K)have been researched at home and abroad in recent years,the preparation process is complicated and the cost is high.It large-scale application cannot be realized in a short time.Therefore,It is imperative to study packaging heat dissipation materials with high thermal conductivity and simple preparation.In this paper,aiming at the technical problem of low thermal conductivity of heat dissipation materials of tungsten and copper alloys,the coating technology is used to prepare tungsten copper coatings on high thermal conductivity copper substrates,which combines the low thermal expansion coefficient of tungsten copper coatings and high thermal conductivity of copper substrates.A new composite heat dissipation material with high thermal conductivity,low thermal expansion coefficient and simple preparation was obtained.According to the visual design method of multi-factors,multi-level and multi-objective,11 groups of experiments with 5 factors and 11 levels were designed.XM-8000 high velocity oxygen fuel was used to prepare tungsten copper coating heat dissipation materials with different powder ratios on an oxygen-free copper substrate.The micro-topography and phase composition of the coating were characterized by an ultra-deep digital microscope,a scanning electron microscope,and an X-ray diffractometer.At the same time,the thermal conductivity,coefficient of thermal expansion(CTE)and microhardness of the samples were analyzed by means of thermal conductivity tester,thermal dilatometer and microhardness tester.etc.The effects of fuel flow,oxygen flow,feeding voltage,carrier gas flow and powder ratio on the thermal conductivity,thermal,coefficient of thermal expansion and microhardness of the composites were studied.The conclusions are as follows:1)The cross-sectional morphology of the sample consists of three parts: the inner deformed matrix,the interface between the coating and the substrate and the surface coating.The cross-section topography of the coating shows that there are no obvious defects and particle inclusions at the interface,and the coating is densely bonded to the substrate.The phase of the composite coating mainly consists of cubic W phase,cubic Cu phase,a small amount of Cu2O and WO3.2)The experimental factors and indicators are analyzed by the multi-factor multi-level multi-objective visual analysis method.The optimum technological parameters for thermal conductivity ? 280W/(m·K),CTE ?9×10-6/K and microhardness?200HV0.2 is obtained as follows: fuel flow 36~38L/h,oxygen flow 500~550L/h,feeding powder voltage 6.5~7.8V,carrier gas flow 400~450L/h,copper mass fraction 16%~20%.3)Two sets of parameters were selected to verify the test within the range of optimum process parameters.When the temperature is 50?,the thermal conductivity of the coating is between 290~310W/(m·K),which is nearly 100W/(m·K)higher than that of the conventional tungsten copper alloy heat sink material.The specific heat capacity and thermal conductivity of the coating increase with increasing temperature,indicating that the higher the temperature,the better thermal properties of the composite.The measured CTE of the coating is between 8~14×10-6/K,and its CTE increases with increasing temperature.Because the higher the temperature,the less the buffering effect of the tungsten copper coating on the thermal expansion of the copper substrate.The microhardness value of both sample coatings reaches 220HV0.2,which is about 70HV0.2 higher than the microhardness of oxygen-free copper substrate.It indicates that the wear resistance of the copper-based tungsten-copper composite heat-dissipating material was improved compared to the substrate of oxygen-free copper.In summary,a low-cost copper-based tungsten-copper composite heatdissipating material with a thermal conductivity as high as 300 W/(m·K)has been successfully prepared.The influence of tungsten copper content and thermal spraying process parameters on the performance of copper-based tungsten-copper composite heat-dissipating material has been studied systematically,which provides practical application reference value for the industrialized production of the composite material.