Study On Liquid Phase In Situ Reaction Preparation Process,Microstructure And Properties Of Cu-Al₂O₃-TiB₂ Composites

Dispersion strengthened copper alloys have been widely applied in many high-tech fields such as high-end electronic devices,rail transit and national defense advanced weapons because of their high strength,high hardness,high conductivity and excellent heat resistance.At present,the studies on dispersion strengthened copper alloy systems mainly focused on the performance improvement and development of single particle strengthened copper alloys.With the rapid development of new high technology,single-phase strengthened dispersion copper alloys will be more difficult to meet the application requirements.The development of dual-phase strengthened dispersion copper alloys and their preparation technology is an effective way to solve the above problems.Therefore,in this paper,a Cu-0.75wt.%Al₂O₃-0.75wt.%TiB₂ composite ingot was prepared by liquid phase in situ reaction casting method and then processed by hot rolling and cold rolling.The microstructure characteristics of as-cast sample,the changes of microstructure and properties during processing were studied by metallographic microscope,scanning electron microscope and transmission electron microscope,and the strengthening mechanism was revealed.Then,based on the traditional liquid phase in situ reaction,a new liquid phase in situ reaction-efficient solidification technology was invented and a new experimental device was developed.Subsequently,a high-performance Cu-0.75wt.%Al₂O₃-0.75wt.%TiB₂ composite was prepared.The following main achievements are obtained:（1）Cu-Ti-B-Al-Cu₂O raw material system was designed based on thermodynamic calculations,and the Cu-TiB₂-Al O₃ composites were prepared by liquid phase in situ reaction method.The kinetic model of liquid phase in situ reaction was established.According to the dynamic analysis:The optimization of raw material ratio,the design of hybrid in situ reaction complex device and the optimization of reaction conditions were important.（2）A Cu-0.75wt.%Al₂O₃-0.75wt.%TiB₂composite was prepared by traditional liquid phase in situ reaction method.Spherical Al₂O₃ particles with a size of 50～500 nm and irregular polygonal TiB₂ particles with a size of 50 nm～1.5μm were formed in the copper matrix.The interface between the strengthening phase particles and the copper matrix was good.However,there was particle agglomeration.（3）With the increase of deformation,the strength and hardness of Cu-0.75wt.%Al₂O₃-0.75wt.%TiB₂ composites increased,and the elongation decreased,while the change of conductivity was small.When the deformation was 90%,the tensile strength,yield strength and hardness increase from 265 MPa,208 MPa and 85 HV to 477 MPa,452 MPa and158 HV respectively,and the elongation decreases from 31.4%to 5.7%,while the conductivity decreases from 81.4%IACS to 80.0%IACS.According to the experimental results and strength model calculations,it was determined that the strengthening mechanisms of the composites were dislocation strengthening,dispersion strengthening and grain boundary strengthening in descending order.（4）According to the thermodynamic and kinetic principles of liquid phase in situ reaction,an idea of combining separate melting of complex reactant raw materials and separate pre-reaction with efficient solidification of composite melt was put forward.A new liquid phase in situ reaction-efficient solidification technology for dual-phase reinforced metal matrix composites was invented and a new experimental device was developed.（5）The complex melt liquid phase in situ reaction composite system based on the integrated control of multi melts pre-reaction and uniform mixing was designed and optimized,which realized the accurate control of multi melts pre-reaction and the homogeneous mixing process of composite melt,and solved the serious problems of coarsening and macro segregation of Al₂O₃ and TiB₂ particles in Cu-Al₂O₃-TiB₂ composites to some extent.（6）With the use of Cu-Ti-B-Al-Cu₂O raw material system,the Cu-0.75wt.%Al₂O₃-0.75wt.%TiB₂ composite was prepared by using the designed liquid phase in situ reaction-efficient solidification.Al₂O₃ and TiB₂ particles with an average radius size of 77.6 nm were evenly distributed.The coarsening and agglomeration of particles were significantly reduced.When the cold rolling deformation was 93.7%,the tensile strength and conductivity of the composites reached 607 MPa and63.5%IACS respectively.（7）Liquid phase in-situ reaction casting combined with large-deformation rolling is a promising process for the preparation of dual-phase reinforced dispersion strengthened copper matrix composites.