Microstructure And Properties Of In-Situ TiC-TiB₂/Cu Composites Prepared By Powder Metallurgy

TiC and TiB2 particles have excellent properties such as high melting point,high hardness,high conductivity,low density and good chemical stability.Adding TiC-TiB2 reinforcement phases into Cu matrix can not only maintain the good thermal conductivity,but also improve the hard and wear resistance of the material.And it can solves the contradiction between hard and conductivity.Therefore,the mechanical alloying process and hot-pressing method were used to prepare the TiB2-TiC/Cu composites with different TiB2-TiC content.The structure and properties of composite powder and composite material's mechanical milling process,the hot-pressing method under argon atmosphere and the different mechanical milling processes were systematically analyzed.The phase composition of(TiB2-TiC)/Cu composites was analyzed by X ray diffraction(XRD).The microstructure,the morphology,size and distribution of the reinforced phase were analyzed by scanning electron microscopy(SEM)and transmission electron microscopy(TEM),respectively.According to the research on the hardness,conductivity and density of the(TiB2-TiC)/Cu composites prepared by different TiB2,TiC content and different milling technology,the conclusion is as follows:(1)Preparation of Cu-TiH2-B4C composite powders by mechanical ball milling process,the higher ball-powder-ratio was,the higher the welding degree of composite powder particles was.When the ball-powder-ratio is increased,the particles of TiH2 and B4C are distributed gradually from cold welding on the surface of Cu particles to the interior of Cu particles,until the uniform distribution of TiH2 and B4C particles in Cu particles is achieved.The structure of composite powder prepared by mechanical ball milling can be adjusted by controlling the ball-powder-ratio.(2)With the increase of mechanical milling time,the morphology of the composite powder particles is gradually welded into a composite powder with a certain thickness.Due to the increase of dislocation density,the composite powder particles are gradually broken and refined.Finally,it reaches the stage of dynamic balance between breakage and welding.The dislocation produced by mechanical ball milling composite powder is the main cause of the broadening of diffraction peak.The dislocation density of Cu-TiH2-B4C composite powder with 20:1 ball-powder-ratio is about 5 times of that of Cu-TiH2-B4C composite powder particle dislocation density.(3)(3%TiB2-1.29%TiC)/Cu composite was prepared by mechanical ball milling and hot-pressing method.The hardness of composites increased with the increase of ball-powder-ratio or the prolonging of ball milling time,and the electrical conductivity decreased gradually.The distribution of TiB2-TiC particles in Cu matrix became more and more dispersed.Also the particles size became smaller,the compactness of the composites is about 92%.The diffraction peak of each phase in the composite shifted to high angle with the prolongation of milling time,but the change of the ball-powder-ratio had no significant effect on it.(4)During hot-pressing method of Cu-TiH2-B4C system,the TiH2 dehydrogenation reaction occurs first,and then several kinds of CuxTiy metal compounds are formed by reaction of Ti and Cu with the increase of sintering temperature.Finally,with the decomposition and diffusion of B4C,the CuxTiY alloy is decomposed,Ti reacts with the diffusion of B and C,and in situ formation of TiB2 and TiC particles at the location of the Ti atoms.The melt CuxTiy mesophase results in the segregation of TiC and TiB2 particles and the adhesion of newly produced TiC and TiB2 particles to form clusters of TiC and TiB2 particles.(5)The composite powders prepared by ball milling and mixing powder process showed a lamellar particle with a certain thickness.The B4C particles have no significant influence on the particle morphology of the composite powders in the ball milling+powder mixing process.The TiB2?TiC reinforced phases produced by in-situ reaction is small,uniformly distributed and dispersed in Cu matrix,without obvious agglomeration.The hardness of(TiB2-TiC)/Cu composites increased with the increase of TiB2?TiC content,but the conductivity decreased gradually,and the density remained around 96%.