Investigation On Microstructure And Properties Of TiB_x(x=1,2)/Cu Composites By Two-beam Melt Reaction Casting

With the rapid development of transportation and electric power industry in China,the requirement of high strength and high conductivity copper materials under actual working conditions is increasingly stringent.TiBx(x=1,2)/Cu composites have become one of the most promising engineering candidate materials with different types and shapes of TiBx(x=1,2)as reinforcing phases to achieve complementary advantages.In this paper,TiBx(x=1,2)composites reinforced by multi-component hybrids were prepared by two-beam melt reaction casting.Firstly,the phase and structure of TiBx(x=1,2)composites obtained under different processing conditions were analyzed;secondly,the electrical conductivity,hardness and tensile properties of TiBx(x=1,2)composites were characterized.By exploring the effects of casting system,cooling rate,second phase content,rolling deformation process and adding mode of rare earth La on the structure and properties of TiBx(x=1,2)composites,the relationship between TiBx(x=1,2)composites preparation process,microstructure evolution and actual properties was systematically analyzed.The main results are as follows:(1)TiBx(x=1,2)/Cu composites were prepared by inversion casting and plug casting respectively.It was found that the composition of plug casting materials was more uniform and the macroscopic uniformity was good.TiBx(x=1,2)/Cu composites were cooled by copper and graphite moulds respectively.Phase analysis showed that the cooling rate had little effect on the type of reinforcement phase.The composites prepared by copper moulds were more uniform in structure and fine in particle size.The hardness and conductivity of the samples obtained were higher than those of graphite moulds.With the increase of the content of the second phase,the size of the reinforcing phase increases,the hardness of the composites increases,and the conductivity decreases.(2)TiBx(x=1,2)/Cu composites prepared by plug casting were treated by two rolling treatments.It was found that the strength of the composites reached 348.7 MPa after cold rolling annealing,while the reinforcing phases TiB2 and TiB reinforcing bodies of TiBx(x=1,2)/Cu composites could be uniformly dispersed in the matrix after hot-cold rolling deformation combined with homogenizing annealing.The maximum strength of TiB reinforcing phases reached 519.6 MPa.The composite material with 2.5%mass fraction of the second phase has the best comprehensive properties after hot and cold rolling.(3)TiBx(x=1,2)/Cu composites were prepared by "plug casting+Z-channel+water-cooled copper mould" casting system.The effect of collision was increased to make the two-beam melt mix fully.The relative content of particles and whiskers in the composites was basically controlled by the design of different mass fractions of the second phase.The composite with 2.5%of the second phase mass fraction has the highest mechanical properties,the best comprehensive properties,75.2%IACS,151.5 HBW hardness,543.0 MPa tensile strength and 519.8 MPa yield strength after homogenizing annealing at 900 C for 3 h,hot rolling for 30%and cold rolling for 90%deformation treatment.Compared with as-cast pure copper,the hardness,tensile strength and yield strength of as-cast pure copper are increased by 2.6 times,2.1 times and 4.2 times under the premise of guaranteeing low damage conductivity.(4)Compared with TiB2/Cu composites,the strength of TiBx(x=1,2)/Cu composites after deformation treatmenthas been increased by 15.1%.The size of dimples in the tensile fracture is small and the number of dimples is large.The phenomenon of particle debonding,whisker debonding and pulling-out can be observed at the fracture.With different physical parameters and occupancy,the advantage complementarity and coupling effect between whiskers can be achieved by large deformation rolling.The mechanical properties and conductivity loss can be optimized with the minimum mass fraction.(5)The electrical conductivity of TiBx(x=1,2)/Cu composites prepared by adding rare earth La in different ways was improved.The mechanical properties were improved by inhibiting the solid solubility of the matrix and melt purification.Based on optimizing the size and distribution of the second phase,the tensile strength of the optimum composites was increased by 11.2%.The best TiBx(x=1,2)/Cu composite has electrical conductivity of 75.5%IACS,hardness of 160.5HBW and tensile strength of 582.7MPa after deformation treatment.