Investigation On Microstructure And Properties Of In-Situ TiB_x(x=1,2)/Cu Composite

Titanium boride(TiBx(x=1,2))have good mechanical properties and high electrical conductivity,which become candidates for engineering applications-Therefore,TiBx(x=1,2)/Cu composites were prepared by vacuum induction melting and in situ reaction method with furnace cooling,graphite mould,copper mould three different cooling methods.The phase constituents and microstructural evolution of the composites were analyzed by X-ray diffraction(XRD),scanning electron microscopy(SEM)and transmission electron microscopy(TEM).The hardness and electrical conductivity of the composites with different chemical compositions were measured.The properties of the composites was further improved by the subsequent treatment.The conclusion is as follows:(1)TiBx(x=1,2)/Cu composites were prepared successfully by furnace cooling.In the composites,morphology of TiB is whisker(aspect ratio(>10)),and the distribution of TiB is relatively uniform;morphology of TiB2 is hexagonal particles,which is easy to cluster together.And the overall distribution of the sample is not uniform.The reinforcement has been floating,and the lower part of the sample has a small amount of Cu4Ti phase.(2)The precipitation of titanium boride from Cu-Ti-B liquid phase was analyzed by thermodynamics and kinetics.For different chemical compositions,the formation of TiB and TiB2 is thermodynamically favored.Due to the different nucleation and growth kinetics conditions,the reinforcement of composites with different chemical compositions is different in the final solidified structure.For example,under certain compositions,The reinforcement of composites contain TiB and TiB2,since the different growth rate of titanium boride during precipitation.in some compositions,the reinforcement of composites contains TiB2,because of the limited nucleation of TiB.(3)TiBx(x=1,2)/Cu composites were successfully prepared by graphite mould.In the composites,the TiB2 particles is easily agglomerated and the TiB whiskers grow along the edges of the agglomerated TiB2 particles.Compared with the furnace cooling,the specific gravity of the composites prepared by graphite molds is obviously reduced,and the solid solution of Ti atoms in the matrix.(4)TiBx(x=1,2)/Cu composites were successfully prepared by copper mould,and the solid solution of Ti atoms in the matrix.The solid solution of Ti atoms and the reinforcements co-enhance the hardness of the composites while reducing the electrical conductivity,but the contribution of the reinforcements relative hardness is significantly larger than the solid solution of Ti atoms.The effect of solid solution Ti on the electrical conductivity of the composites is more than twice that of the reinforcements.Compared with the furnace cold and graphite mould,the second phase of the composites prepared by the copper mould has smaller particle size and the whole distribution of the sample is more uniform.(5)The dislocation density of Cu matrix prepared by cold deformation treatment of TiBx(x=1,2)/Cu composites prepared by copper mould is greatly increased.Its hardness are greatly improved,the conductivity has declined.After the heat treatment,the dislocation density in the composites is obviously reduced,and twins are produced.The matrix of composites precipitate Cu4Ti phase.After heat treatment at 450℃ for 2h,the good properties were obtained.