Preparation And Properties Of TiB₂-Diamond/Cu Composites

Copper matrix composites are widely used in electrical contacts and brush electrodesand other fields, which not only possess high electrical and thermal conductivity of copperand its alloys, but also make up for its lower strength and wear resistance. Titaniumdiboride is a promising candidate for the reinforcement of copper because of its highhardness, superior wear resistance, low thermal expansion coefficient and good propertiesof electrical and thermal conductivity. At the same time diamond has the highest hardnessamong all natural materials conferring it high abrasion resistance. Both of them areexpected to be added to the copper matrix with acquiring excellent overall performance.Firstly TiB2and diamond powder were surface modificated by an electroless platingprocess to improve the interfacial bonding with the copper matrix. Afterwards phases wereanalysed with X-ray diffraction (XRD) for the composite powder, and then the platingconditions of the particles were observed by scanning electron microscopy (SEM). Bymeans of spark plasma sintering (SPS) method, copper matrix composites were producedwith titanium diboride and diamond as the reinforcement together. The optimal sinteringprocess parameters were obtained by testing the density, tensile strength, electricalconductivity and hardness of the materials. The surface morphology and the tensilefracture morphology were observed by SEM. By using field emission transmissionelectron microscope (TEM), the microstructure of TiB2and diamond as well as theinterface binding between them and the copper matrix were analyzed.The results showed that the TiB2and diamond powder surface were coated with acopper layer (0.5~1μm) after the electroless. The plating was uniform, dense and no sharpedges, which improved the interface bonding state between TiB2or diamond and thecopper matrix, as a result the mechanical performance improved.The optimal sintering parameters were: the sintering temperature was910℃and theholding time was10min. Under the conditions, the performance of TiB2-2wt.%-Diamond-0.5wt.%/Cu composite material as follows: density was8.45g/cm3, tensile strength was291.3MPa, hardness was810MPa, the electrical conductivity was64%IACS. Additionally,the density and the electrical conductivity of the composites decreased with the increase of TiB2and diamond content. While the hardness and the tensile strength of the compositesall gradually increased first then the rising tendency became slower with the increase ofthe enforcement particles. Furthermore, the effect of mixed enforcement was better thanthat of a single particle.The TEM results revealed that TiB2and diamond maintained intact in the coppermatrix. Nanometer copper coating as the transitional layer played a important role inimproving the interface bonding strength. The TEM also indicated: there was weakinteraction between the copper coating and TiB2, but no interfacial reactions withdiamond.