Preparation Technology And Microstructure And Properties Of Machinable Diamond/Aluminum Composites

With the rapid development of electronic devices towards miniaturization and high integration,the heat dissipation problem has become increasingly severe.Thus,there is an urgent need to develop a new generation of high thermal conductivity thermal management materials.Diamond-reinforced metal matrix composites are gaining significant attention as thermal management materials due to diamonds’ extremely high thermal conductivity and very low coefficient of thermal expansion.However,there exist prominent interface incompatibility issues between diamond and most high thermal conductivity metals.These issues include poor interfacial bonding,high interfacial thermal resistance,and high residual stresses resulting from thermal and elastic mismatches.Moreover,the machinability of diamond-reinforced metal matrix composites is also poor,which severely hinders their applications.Based on the above issues,in this paper,diamond/Al composites were studied,and a nano-carbide coating was prepared on the diamond surface to enhance its interface bonding and thermal conductivity.To improve the machinability,this paper explores the feasibility of using small-sized diamond particles as raw material,reducing the thermal resistance by surface treatment,and increasing the diamond content by gradation design.To meet the demand for structural components with thermal diffusion,the thermal deformation behavior and the thermal extrusion process are studied and optimized using finite element simulation and experimental methods.To ensure long-term service performance,the effects of thermal cycling on the residual stress,microstructure,and properties of diamond/Al composites are investigated.The main results are as follows:(1)A method combining sol-gel and the in-situ reaction was used to prepare nanoWC coating on the diamond surface,and WC-coated diamond/Al composites were prepared by powder metallurgy.The effect of coating thickness and interface structure on the thermal conductivity of composites was analyzed.The results show that,compared with uncoated diamond,WC coating can effectively improve the bonding between diamond and Al matrix,thus enhancing the density and thermal conductivity of the composites.However,excessively thick WC coating often causes interface cracking,which weakens its improvement effect.In order to improve the uniformity of the coating,diamond particles were subjected to high-temperature oxidation pretreatment before the preparation of WC coating and diamond/Al composites.The results showed that the WC coating applied after the oxidation treatment reacted with aluminum during the preparation of composites,forming Al12 W and Al4C3,which led to a decrease in thermal conductivity.(2)Using crushed diamond particles with small sizes(<100 μm)as raw materials,a method that combines the sol-gel method and the in situ reaction was used to coat their surfaces with nano-SiC.A three-dimensional realistic particle model was established to simulate the stacking process of diamond particles,and a diamond stacking model was used to optimize the grading scheme.In the preparation of composites,although the SiC coating will react with the Al to form a small amount of Al4C3,it can still effectively enhance the interfacial bonding and heat transfer effect of the composite,increase its density and thermal conductivity.The gradation parameters of different diamond particle sizes were simulated,and the simulation results were verified by experiments.The results showed that the grading simulation results were consistent with the experimental results.However,during the powder metallurgy process,the Al powder was unable to fill the pores of the diamond particles,leading to voids in the samples and a decrease in their thermal conductivity.After grading and SiC coating treatment,the thermal conductivity of the crushed diamond/Al composite can be comparable to that of the single crystal diamond/Al composite,while having better machinability.(3)The thermal deformation behavior of SiC-coated diamond/Al composite with a diamond volume fraction of 25%was studied using hot compression experiments.Based on the stress-strain curve,the thermal deformation constitutive equation and processing map of the composite were established to provide a basis for subsequent extrusion process parameters.The effects of preheating temperature and extrusion speed on the extrusion process of SiC-coated diamond/Al composite were analyzed using DEFORM 3D software to guide the optimization of the extrusion process of the composite.The extrusion temperature was selected and optimized according to the simulation results and thermal processing map.and L-shaped sections of composites with different diamond particle sizes were successfully prepared.The structure and properties of the extruded and T6-state(solution treatment and artificial aging)composites were studied.The results showed that as the diamond particle size decreased,the strength of the extruded composite increased,but the plasticity decreased.T6 heat treatment could improve the strength of the composite,but the strength trend with diamond particle size was opposite to that of the extruded composite.As the diamond particle size decreased,the thermal conductivity of both states of composites decreased slightly.(4)The stability of the structure and properties of SiC-coated diamond/Al composite was studied under simulated space environment thermal cycling and accelerated thermal cycling conditions.Firstly,the effect of thermal cycling on the residual stress of the diamond/Al composite was studied using finite element simulation,and the performance of the material after multiple thermal cycling was experimentally studied.The results showed that after thermal cycling,the residual stress in the composite was mainly concentrated inside the diamond particles,while the plastic deformation of the Al matrix mainly occurred around the interface between the diamond particles and the matrix,as well as in the region between the two particles.The plastic deformation of the matrix accumulated gradually with increasing cycling times,which could ultimately lead to the cracking of the diamond particles or interface.Overall,SiC-coated diamond/Al composite exhibits good stability of properties.