Fabrication And Properties Of The Copper Matrix Composites Reinforced With TiB₂/TiC_x-TiB₂Particles

Copper is widely used in industrial applications due to its high electrical conductivityand ductility. However, the relatively low hardness, low strength, poor wear resistance,oxidation and deformation easily above500oC lead to excessive consumption of the copper.In recent years, ceramic particles reinforced copper matrix composites develop rapidly dueto the high hardness and high strength, better wear resistance and oxidation resistance, lowthermal expansion coefficient, as well as easy fabrication and low cost of the composites.The TiC and TiB₂ceramics exhibit high melting point, high hardness, high electricalconductivity, high modulus, low density and better chemical stability. Therefore, theincorporation of TiC and TiB₂ceramics into the copper matrix would improve the strengthand wear resistance of the composites without the large sacrifice of the thermal and electricalconductivities. Combustion synthesis （CS） has several advantages, such as the simpleprocess, saving energy, high production efficiency and high purity of the products. However,the products are hard to densification. Moreover, the research on the ceramic particlesreinforced copper matrix composite by the CS and hot press consolidation is rather limited.In the present study, Cu-Ti-B/B4C systems were selected as the objectives. The in-situTiB₂and TiC_x-TiB₂particles reinforced copper matrix composites with high hardness, highstrength and high wear resistance were fabricated successfully by the CS and hot pressconsolidation method. The effects of the TiB₂and TiC_x-TiB₂contents, as well as the Cr andZr contents on the microstructures, compression properties and abrasive wear properties ofthe composites were studied. The wear mechanism of the copper matrix compositesreinforced with TiB₂and TiC_x-TiB₂was initially revealed. In addition, the effects of the TiB₂and TiC_x-TiB₂contents on the electrical conductivity, thermal expansion coefficient andthermal conductivity of the copper matrix composites were also investigated. The mainresults of the study are as follows:（1） The TiB₂and TiC_x-TiB₂particles reinforced copper matrix composites have been successfully fabricated by the CS and hot press consolidation method in the Cu-Ti-B/B4Csystems. It reveals that the yiled strength, ultimate compression strength andmicrohardness of the composites increase with the increase of the ceramic particlecontents. When the ceramic content is less than60vol.%, the yiled strength, ultimatecompression strength and microhardness of the TiC_x-TiB₂/Cu composites are higher thanthat of the TiB₂/Cu composites due to the fine ceramic particles; When the ceramiccontent is60vol.%, the yiled strength, ultimate compression strength and microhardnessof the TiB₂/Cu composites are higher than that of the TiC_x-TiB₂/Cu composites due to thehigher hardness of TiB₂.（2） It reveals that the effect of the Cr and Zr addtion on the compression properties of theTiB₂/TiC_x-TiB₂particles reinforced copper matrix composites. The crystal lattice of theα-copper becomes distortion due to the solution of Cr and Zr in the copper matrix,therefore, the stress field turns to be stronger, and the yield strength, ultimatecompression strength and microhardness of the composites increase with the increasingCr and Zr content. In addition, the yield strength, ultimate compression strength andmicrohardness of the composites increase due to the solution of Zr in the TiCxand TiB₂particles. The effect of Zr addition in the TiB₂/Cu composites is obvious than that in theTiC_x-TiB₂/Cu composites. In the TiB₂/Cu composites, when the Zr content is5wt.%, theyiled strength, ultimate compression strength and microhardness are improved by98%,88%and52%, respectively; While, in the TiC_x-TiB₂/Cu composites, when the Zr contentis7wt.%, the yiled strength, ultimate compression strength and microhardness areimproved by65%,45%and59%, respectively. The properties of the composites with theaddition of Zr are better than that of the composites with the addition of Cr.（3） It reveals the regularity that the volume losses of the composites reinforced withTiB₂/TiC_x-TiB₂increase with the increase of the applied loads and abrasives. When theceramic content is60vol.%, the wear resistance of the TiB₂/Cu and TiC_x-TiB₂/Cucomposites is improved by3.3and3.4times compared with pure copper. It reveals thewear mechanism of the copper matrix composites: First, the Al₂O₃abrasive particlespenetrate into the soft copper matrix and cut it, leading to excessive copper removal fromthe composites. Meanwhile, the Al₂O₃abrasives also have an impact on the TiCxandTiB₂ceramic particles, resulting in the blunting of the Al₂O₃abrasives. In the secondstage, the TiCxand TiB₂ceramic particles expose from the copper matrix and they act asa barrier to the micro-cutting action of the abrasives, inducing the decrease in the cutting efficiency of the Al₂O₃abrasives and the consequent volume loss of the composites.When the exposed TiCxand TiB₂ceramic particles escape from the worn surface of thecomposites, the Al₂O₃abrasives will impact the copper matrix and the TiC_x-TiB₂ceramicparticles simultaneously again.（4） It reveals the regularity and mechanism of the electrical conductivity for the coppermatrix composites with different contents of TiB₂/TiC_x-TiB₂, Cr and Zr elements: as thecontents of ceramic particles and elements increase, the scattering areas of the freeelectron increase, and the interface scattering becomes stronger, leading to the lowelectrical conductivity of the composites. The electrical conductivity of the TiB₂/Cucomposites is higher than that of the TiC_x-TiB₂/Cu composites due to the higherelectrical conductivity of the TiB₂particle. It reveals the regularity of the thermalexpansion coefficient and thermal conductivity for the copper matrix composites withdifferent ceramic particle contents and tempreture: the thermal expansion coefficient andthermal conductivity of the composites decrease with the increasing ceramic particlecontents; As the temperature increases, the thermal expansion coefficient of thecomposites increases, while the thermal conductivity of the composites decreases. Thethermal expansion coefficient and thermal conductivity of the TiB₂/Cu composites islower than that of the TiC_x-TiB₂/Cu composites due to the lower thermal expansioncoefficient and thermal conductivity of the TiB₂particle.