Interface Microstructure And Thermal Properties Of Diamond Particles Reinforced Al Matrix Composite

The development of electronic power devices in aerospace industry to miniaturization,lightweight,high power density and high performance has become a key problem in restricting the reliability and efficiency of electronic equipment.Therefore,the thermal management materials with low density and high thermal conductivity are urgently needed.In the present work,diamond particles reinforced aluminum(diamond/Al)composites with ultrahigh thermal conductivity were designed and successfully prepared by squ eeze casting method.The microstructure evolution mechanism,the mechanical behavior,the thermal conductivity and the corresponding thermal cycling stability of the composites were studied by scanning electron microscopy,transmission electron microscopy,laser thermal conductivity measurement and three-point bending tests.Based on the analysis of the interface heat transfer characteristics and the existing thermal conductivity model,a method for predicting the thermal conductivity performance of diamond/Al composites has been proposed.Based on Hasselman-Johnson model,diamond particle size between 40 to 200 ?m were chosen as research object.Moreover,interfacial thermal resistance calculation results indicated that the formation of Al4C3 with thickness less than 840 nm is beneficial for the thermal conductivity.Based on interfacial reaction kinetics,in order to fully infiltrate Al into diamond preform and control the interfacial reaction between diamond and Al,a modified squeeze casting method with prolonged densification time,higher infiltration temperature and lower cooling rate was designed,and the diamond/Al composites with high relative density,controlled interfacial microstructure and ultrahigh thermal conductivity have been prepared.The interfacial bonding of diamond/Al composites has been evolved from fully debonded interface to selected bonded interface and finally to the fully adhered interface by modification of the preparation parameters.In diamond/Al composites with fully adhered interface,the(111)planes of diamond particles was direct bonded with Al matrix,while the(100)planes of diamond particles was reactive bonded with Al matrix with two morphology Al 4C3(rod-like and platelet-like).The long axis lateral side of the Al4C3 was smoothly bonded with the Al matrix,which is consistent with the step growth model.However,the end of the Al4C3 was roughly bonded with the Al matrix,which is consistent with the continuous growth model.Moreover,the rod-like Al4C3 was mainly formed by the random orientation growth of Al4C3 toward Al matrix while the platelet-like Al4C3 was mainly formed by the certain orientation growth(200)diamond?(003)carbide,[011]diamond?[110]carbide found in the present work)which is parallel to the surface of diamond particles.When changed from fully debonded interface to the fully adhered interface,the bending strength of diamond/Al composites has been increased from 38 to 220 MPa,which has been increased 479%.Moreover,when the particle size of diamond was increased from 40 to 200 ?m,the bending strength of diamond/Al composites has been decreased from 287 to 171 MPa.When changed from fully debonded interface to the fully adhered interface,the thermal conductivity of diamond/Al composites has been increased from 104 to 603 W/(m·K),which has been increased 480%.when the thermal conductivity of diamond particles raised about 200 W/(m·K),the thermal conductivity of diamond/Al composites has been increased 30 W/(m·K).Moreover,when the particle size of diamond increased from 40 to 200 ?m,the thermal conductivity of diamond/Al composites has been increased from 468 to 670 W/(m·K).After analyzing the heat transfer characteristics of the composites with interfacial debonding and the reaction products and based on Hasselman-Johnson model,the thermal conductivity of diamond/Al composites with fully adhered interface could been well calculated by adopting the secondary classification with adding the reinforcement(0.33% error).During thermal cycling process,the interface debonding was mainly occurred at the diamond(111)/aluminum interfaces.Small particle size had better thermal cycling stability in terms of the microstructure and properties of the composites.After 200 cycles from-65? to150?,the thermal conductivity of composites corresponded to 40,70,100 and 200?m diamond particles decreased by 6.5%,7.1%,9.4% and 12.9%,respectively.By comprehensive investigation of the mechanical properties,the initial thermal conductivity,the stability of the microstructure and the thermal conductivity during the thermal cycle of the diamond/aluminum composites,the preferred diameter of the diamond/aluminum composites for heat management were 70 ~ 100?m.