Investigation On Preparation,Microstructure And Properties Of TiB₂/Cu Composites With Controllable Reinforcement Distribution

The regulation of reinforcement configuration is an effective way to develop high performance metal matrix composites.In this subject,TiB₂/Cu composites with obvious difference in microstructure were prepared by powder metallurgy method,and the mixing process and the initial powder form were changed in this.process.The relationship between microstructure and properties was summarized.On this basis,the heterogeneous structure TiB₂/Cu composites were prepared through experimental design,and the influence of the heterogeneity of microstructure on the properties of composites was also studied.The phase constituents and nicrostructural characterization of the composites were analyzed by X-ray diffraction（XRD）,scanning electron microscopy（SEM）and transmission electron microscopy（TEM）.And the hardness,electrical conductivity and tensile properties of the composites with different distribution were tested.The main results are as follows:（1）Composite powders were made by mechanical mixing and ball milling with Cu、B powder and different sizes Ti powder,then TiB₂/Cu composites were prepared by molding and sintering.The results show that the second phase of composites obtained by ball milling is more homogeneous and dispersed compared with those by mechanical mixing,and the mechanical properties of the composite are better,but the electrical conductivity is lower.The composites with smaller second phase size and less agglomeration can be obtained with smaller size Ti powder when the same mixing process was used,and these composites have better comprehensive properties.（2）TiB₂/Cu composites were prepared by atomized spherical Copper powder with different sizes.The homogeneous reinforcement in the composite can be obtained macroscopic ally when the copper powder size is 1μm,and it has a lower electrical conductivity,but the highest hardness.With the increase of powder size,the second phase is connected to a three-dimensional network structure,and it shows a inhomogeneous distribution in the matrix.The electrical conductivity increased,but the hardness decreased.The results show that the three-dimensional network structure is beneficial to the improvement of the electrical conductivity.（3）Composites with different heterogeneity degree were prepared through changing the mass percentage of copper power involved in ball milling by means of combining ball milling and mechanical mixing,so as to achieve controllable preparation of inhomogeneous reinforcement.Its microstructure is composed of the reinforcement-rich zone and the reinforcement-poor zone.With the increase of the mass percentage,the microstructure of the composite tends to homogenization macroscopically,but it is still inhomogeneous on the microscale.The electrical conductivity of the composites gradually decreases,and the hardness increases linearly.（4）In the TiB₂/Cu composites with heterogeneous structure,the copper powder involved in ball milling is beneficial to the improvement of tensile strength,and the addition of Cu powder in mechanical mixing process can improve the plasticity of composites.（5）The aggregation degree of reinforcements has an important effect on the properties of TiB₂/Cu composites,and proper cold deformation can significantly improve the comprehensive properties.The composite obtained by mechanical mixing has the most excellent comprehensive properties after the deformation treatment.In the composites with heterogeneous structure,the comprehensive properties increases gradually with the increase of macroscopic homogenization of the reinforcement,and it can reach the best when the mass percentage of copper power involved in ball milling is 90%.