Effect Of Rare Earth Elements On Microstructure And Properties Of TiB_x（x=1,2）/Cu Composites Prepared By In Situ Reaction

Power transmission,electronic information,rail transportation and other fields which require copper materials to have high electrical conductivity,thermal conductivity,high strength,wear resistance and high temperature resistance.Therefore,the high electrical conductivity and high thermal conductivity of copper and high strength,low thermal expansion,resistance TiB_2pand TiB_w ceramic reinforcements with different morphologies resistant to high temperatures are compounded effectively to prepare multi stages and multi phases hybrid reinforced copper matrix composites which have a wide application prospects.The reinforcements prepared by in situ reaction method which has good interfacial compatibility with the matrix,wheras the liquid phase reaction exsists the problems of the reinforcements agglomeration and the introduction of harmful impurity elements easily,the addition of rare earth elements can effectively purify and refine（modified）and（micro）alloyed melts,thereby improving the metallurgical and forming process and the comprehensive properties of the materials.In this study,the Cu-Ti-B system is selected,TiB_x（x=1,2）/Cu-La and TiB_x（x=1,2）/Cu-Ce composites are prepared by in situ reaction technology of Cu-B and Cu-Ti double beam melts.In order to prepare a copper matrix composites with excellent microstructure and better properties,the rare earth elements are introduced into the in situ reaction of the double beam melts.The effects of rare earth elements La and Ce on the microstructure and properties of TiB_x（x=1,2）/Cu composites were studied,and the changes of morphology,size,distribution of the two reinforcements and the variation of grain size of copper matrix of the composites were analyzed.The mechanical and electrical properties of the composites are explored,and the strengthening mechanism of the composites with rare earth elements is clarified.Research indicates:（1）It indicates that the reinforcements of TiB_2p and TiB_w are successfully formed in the copper matrix by in situ reaction of double beam melts.The addition of the rare earth elements La and Ce did not substantially change the kind of reinforcements,and there are no other heterogeneous phases were formed,the interface between the reinforcements and matrix is well combined.（2）There are two main advantages in improving the microstructure of TiB_x（x=1,2）/Cu composites with addion of La and Ce:both reinforcements and matrix grains are refined,and the reinforcements are more uniformly distributed in the matrix.The two reinforcements TiB_2pand TiB_w in TiB_x（x=1,2）/Cu-La composites with an average size of 0.76μm and 0.84μm,respectively,and the Cu grain size was 0.33μm.The average TiB_2p and TiB_w sizes of the TiB_x（x=1,2）/Cu-Ce composites were 0.55μm and 0.60μm,respectively,and the Cu grain size was0.38μm.（3）The electrical conductivity and strength of the TiB_x（x=1,2）/Cu composites with addition of the rare earth elements La and Ce and combining with deformation treatment can improved respectively.The electrical conductivity and strength of the TiB_x（x=1,2）/Cu-0.04La composites reached 80.2%IACS and 598MPa.The electrical conductivity and strength of TiB_x（x=1,2）/Cu-0.04Ce composites reached 78.4%IACS and 671MPa respectively.（4）It is shown that the addition of rare earths refined the reinforcements and copper matrix grains combined with the deformation work hardening,playing the role of dispersion strengthening of the reinforcements and fine grain strengthening of the copper matrix,improved the strength of the composites finally.Rare earth elements purified the double beam melts in the composites,weakened the scattering of the impurity elements to electrons in the composites,and the effect on improving the electrical conductivity is significantly stronger than the adverse effect of the grain boundaries on electron scattering due to grain refinement.（5）It is found that the La has a more significant improvement on the electrical conductivity to TiB_x（x=1,2）/Cu composites and the Ce has a more significant improvement on the strength to TiB_x（x=1,2）/Cu composites at the same content.