Microstructure,Performance And Finite Element Simulation Of In-Situ Ceramic Reinforced Copper Matrix Composites

Copper（Cu）matrix composites doped with heterogeneous ceramic,graphite and other second phases can significantly enhance their strength and wear resistance,while fully utilizing the excellent thermophysical and tribological characteristics of the Cu matrix,thus expanding their application as special functional materials in the fields of electronic packaging,thermal conductive components and friction materials.At present,how to select suitable reinforcing phases and give full play to their reinforcing effect in the Cu matrix,and achieve the optimal control of the reinforcing phase and the microstructure of Cu matrix are the focus of most studies.However,the quantitative relationship between the microstructure of composites and their macroscopic performance characteristics,the effects of reinforcing phase on the comprehensive performance of composites and the enhancement mechanism need to be further explored.Therefore,it is of great theoretical significance and practical engineering value to develop the research on the microstructure,mechanical properties and damage evolution of Cu matrix composites with reinforced phase,to reveal the effect mechanism of the microstructure on the performance for the configuration optimization of composites and to maximize the strengthening effect of reinforced phases.In this paper,TiB₂/Cu composites,（TiC+TiB₂）/Cu composites and TiC-modified graphite/Cu composites were prepared by hot pressing sintering or direct current resistive sintering,and the microstructure and performance characteristics of the composites had been investigated.Microstructure-based three-dimensional representative volume element models were established to reveal the effects of the types,size distribution,morphology of the reinforcing phase particles and their interfacial bonding with the Cu matrix on the comprehensive performance of the composites and the reinforcing mechanism by finite element analysis.The corresponding optimization strategies and development directions were proposed.The main innovations of this paper are as follows:（1）According to the microstructural characteristics,thermophysical properties and mechanical properties of in-situ 50 vol.%TiB₂ and TiC+TiB₂ reinforced Cu matrix composites,it was revealed that the high content of ceramics could significantly reduce the coefficient of thermal expansion of the Cu matrix composites（about 53%less than pure Cu）,and the thermal conductivity and mechanical properties of the（TiC+TiB₂）/Cu composites were superior to those of the TiB₂/Cu composites.The thermal conductivity（121.2 W/m·K）,yield strength（998 MPa）and elongation（3.1%）of（TiC+TiB₂）/Cu composites were increased by 11.0%,10.4%,and and 6.9%,respectively,compared to those of TiB₂/Cu composites.Combined with the miscrostructure-based finite element simulations,it was revealed that the ceramic particles will induce thermal residual stress and lead to dislocation stacking,which increases the strength and decreases the coefficient of thermal expansion of the composites.The（TiC+TiB₂）/Cu composites with higher thermal residual stresses will produce larger elastic recovery and intensify phonon collisions,resulting in higher rates of change in thermal expansion and thermal conduction.The spherical TiC particles in the（TiC+TiB₂）/Cu composites contribute to optimize the thermal conduction path of the composites and mitigate the stress and strain concentration in the Cu matrix,improving the thermal conductivity and mechanical properties of the composites.（2）Based on the microstructure,thermal conductivity and mechanical performacne characteristics of the low content in-situ TiB₂/Cu composites,it was revealed that the TiB₂/Cu composites sintered by direct current resistance sintering exhibited high strength and thermal conductivity.When the TiB₂ content is 2.5 wt.%,the thermal conductivity and yield strength of the composites at room temperature were 322.1 W/m·K and 174 MPa,respectively,which were 19.1%lower and 155.9%higher than those of pure Cu.The increase of TiB₂ content would improve the load-bearing capacity of the ceramic and matrix,thus enhancing the strength of the composites.However,smaller particle spacing exacerbates the concentration of stress and strain in the matrix and impedes the Cu matrix’s heat conduction,leading to a decrease in thermal conductivity and elongation of the composite.（3）Simulation results based on the micromechanical behavior of composite microstructures revealed that the main failure mechanism of high content ceramic particles reinforced Cu matrix composites is interfacial debonding and ductile damage of the metal matrix,while low content ceramic particles reinforced Cu matrix composites is ductile damage of the metal matrix.The hexagonal TiB₂ particles help to bear the stress,but exacerbate the stress and strain concentration at the sharp corners of the particles,which induces the development of interfacial microcracks or the failure of the matrix.Subsequently,the microcracks connect with each other to form the main crack and expand along the high stress direction,leading to the failure fracture of the composites.（4）Based on the configuration optimization strategy of particle reinforced metal matrix composites,including particle size distribution,morphology and interfacial bonding,it was revealed that the strength of the composites depends on the load-bearing capacity of the particles and matrix;the stress and strain concentration of the matrix will directly determine the ductility of the composites;and the initiation and extension of the initial cracks in the composites is directly related to the damage and failure modes of the materials.The fracture strength and elongation of composites with normal distribution of particle sizes（1,0.2）were 636 MPa and 12.9%,respectively,which were 4.1%and 10.3%higher than those of composites with uniform size distribution.Appropriate size differences between particles can improve the mechanical properties of composites by mitigating stress and strain concentrations in the matrix interstitial to particles.In contrast,oversized particles may lead to stress accumulation,which can exacerbate the damage and failure of the matrix around the particles.The reduction of interfacial strength will significantly reduce the load-bearing capacity of the particles.The reduction of the interfacial strength will also lead to a change in the failure evolution of the composite from initial cracking within the matrix caused by stress-strain concentration to interfacial failure caused by interfacial debonding.Particle morphology has a greater effect on the elongation of the composites and a lesser effect on their strength.The elongation of composites with circular particles was 30.5%higher than that of composites with square particles.The sharp corners of the particles tend to cause stress and strain concentration,which eventually lead to damage accumulation and accelerated failure of the composites.（5）Based on the strengthening mechanism and optimization direction of in-situ TiC ceramics on the mechanical properties and tribological characteristics of graphite/Cu composites,it was revealed that the dense in-situ TiC layer distributes between the Cu matrix and graphite strengthens the Cu matrix,and optimizes the interfacial bonding and stress transfer as the reinforcing phase,which effectively avoids graphite fracture and detachment.The yield strength,compression fracture strength and flexural fracture strength of TiC-modified graphite/Cu composite were increased by 93.1%,37.1%and 97.5%compared with those of TiC-free graphite/Cu composite,while the exogenous TiC particles further deteriorated the mechanical properties of the graphite/Cu composites.Further refining the size of graphite particles could help the TiC ceramic layer to bear the stress and further improve the strength of graphite/Cu composite.When the friction force fails to break the interfacial bonding and lead to TiC ceramic layer shedding,graphite and TiC ceramic layers can take advantage of their lubrication and resistance to plastic deformation,respectively,to reduce the fluctuation of friction coefficient and wear rate.The corresponding wear rate of TiC-modified graphite/Cu composite was 29.7%lower than that of the graphite/Cu composite without TiC.