Fabrication And Properties Of In Situ Copper Matrix Composite Reinforced By TiB₂

In this paper, the in-situ synthesis was adopted to fabricate TiB₂/Cu composites with volume fraction of 5%, 10%, 15%.The microstructure and phase of the composites were observed and analyzed by using XRD, SEM and TEM. The ambient tensile properties, electronic conductivity and tribological properties in dry sliding condition were analyzed.The thermodynamic data for the reactions between B and Ti in the copper were analyzed; the copper matrix composites reinforced by in-situ TiB₂ particles were prepared by reactions of copper, titanium and boron powders. By mechanical milling technique, through cold-pressing, TiB₂/Cu composites with volume fraction of 5%, 10%, 15% and matrix copper were fabricated by reactive hot pressing. By ball-milling technique, another TiB₂/Cu composite with volume fraction 10% was fabricated under the same way.The observation of the microstructure of the composite indicated that TiB₂ particles were homogeneously distributed in the copper matrix, and the size of the TiB₂ particles is from 200nm to 1μm.The results of the mechanical properties test of the composites showed that tensile strength of the composites increased with increasing volume fraction while elongation decreased with increasing volume fraction. The tensile strength increased from 190.7MPa of pure copper to 382.2 MPa of 15vol.% TiB₂/Cu composite. As tensile strength of the 10vol.% TiB₂/Cu fabricated by using the ball-milling, is 565.6MPa, which is one more time higher than that of one using the mechanical mixing powder.The conductivity of TiB₂/Cu composites was studied by using MICROHM METER ZY9858.With increasing the volume fraction of the TiB₂, the conductivity of the composites decreased. For example, the IACS decreased from 93.5% of pure copper to 71.25% of 15vol.% TiB₂/Cu. Some important parameters affect the electronic conductivity of the TiB₂/Cu composites, such as size of the TiB₂ particles, distribution of the TiB₂ particles and condition of the TiB₂ particles with the copper matrix. The IACS of 10vol.%TiB₂/Cu composites is 50.7%, which is fabricated after ball-milling powders.The results of the tribological test of the materials showed that the wear rate and friction coefficient increased with increasing friction load. These indicated that the TiB₂ particles could increase the wear resistance of the composites. When the load was over 80N, the wear rate and friction coefficient of the 10vol.% and 15vol.%TiB₂/Cu increased sharply.As the copper matrix and 5vol.% TiB₂/Cu, the worn surface morphologies were observed with a scanning electron microscope. It has been found that the wear mechanisms of the composite and copper matrix were similar as adhesive wear accompanied by oxidation wear. When the load is between 40N and 80N, the wear mechanisms of 10vol.% and 15vol.%TiB₂/Cu is similar as copper matrix. When the load is over 80N, the wear mechanisms of 10vol.% and 15vol.%TiB₂/Cu were similar as grain-abrasion wear accompanied by oxidation wear.