Hot-Pressing Sintering and Hot-Rolling Strengthening of Small Amount of WC-Reinforced Copper-Based Materials
Numerous studies had shown that particle dispersion strengthening was an effective means to prepare high-performance copper matrix composites.l％WC/Cu and 2％WC/Cu composites with uniform dispersion and distribution were prepared by adding a small amount of WC hard ceramic particles to copper powder by mechanical ball milling and combined with the vacuum hot pressing sintering process.The effect of sintering temperature on the microstructure and physical properties of the composites was also investigated.The microstructure observation mainly involved X-ray diffractometer(XRD),field emission scanning electron microscope(SEM)and transmission electron microscope(TEM).The characterization of physical properties mainly included the determination of relative density,Vickers hardness,electrical conductivity,thermal conductivity and tensile strength.The results showed that:on the one hand,SEM image of the composite block demonstrated that WC particles were uniformly dispersed,and the uniformity did not change significantly with the increase of the sintering temperature,and the distribution of WC particles on the copper matrix after sintering still largely depended on the distribution of WC particles on the copper particles after ball milling.On the other hand,the high-resolution TEM image confirmed the existence of WC particles,and XRD patterns signified that the WC/Cu composite was composed of WC phase and Cu phase during the whole process,and the composite phase transition did not occur with the increase of sintering temperature,and the composite material was finally determined to be WC/Cu matrix composite material.Secondly,with the increase of sintering temperature,the relative density,electrical conductivity,thermal conductivity and Vickers hardness of WC/Cu-based sintered block gradually increased.When the sintering temperature increased from 975 to 1050 ℃,the relative density of 1％WC/Cu composite increased from 97.1％to fully dense(100％),and its Vickers hardness increased from HV 63.8 to HV 99.7,and the electrical conductivity increased from 98.3％IACS(International Annealed Copper Standard Resistivity)to 100％IACS,and the thermal conductivity at room temperature increased from 334.1 to 358.6 W·m-1·K-1.The relative density of 2％WC/Cu composite could also increase from 94.3％to fully dense(100％),and its Vickers hardness increased from HV 76.1 to HV 105.7,and its electrical conductivity also increased from 92.2％IACS to 100％IACS,and the thermal conductivity increased from 306.8 to 373.6 W·m-1·K-1.In fact,higher hot-pressing sintering temperature could improve the densification level of composites,and with the increase of the hot-pressing sintering temperature,the change trend of Vickers hardness,electrical conductivity and thermal conductivity of composite block was synchronized with the change trend of relative density to a certain degree,in which the corresponding increase in surface hardness was closely related to the degree of densification,and the degree of densification indirectly affected the change of electrical conductivity,while the change trend of thermal conductivity was almost the same as the change of electrical conductivity.Practically,it conformed to the Weidmann-Franz law that the thermal conductivity and electrical conductivity of metals were linearly proportional at room temperature.In addition,considering the limited strengthening effect of a single sintering process and the good plasticity of the composite block after hot pressing,the composite block at hot-pressing sintering temperature of 1050 ℃ was hot-rolled and composited.Comparing and observing cross-section TEM images of the samples before and after hot rolling,it could be seen that most of the dislocation fringes before hot rolling were distributed on the copper grains,and a few were distributed next to WC particles.Combined with the tensile curve before hot rolling,it could be judged that the sample had a plastic fracture model before hot rolling,which essentially indicated that the dislocation plugging effect under the Orowan strengthening mechanism before hot rolling was not fully exerted,and the tensile strength of the composite material was not fully realized,and the performance was more determined by the strength of the copper matrix itself.After hot rolling,it could be clearly seen that many dislocations surrounded the WC particles to form a plug,which was a typical feature of the Orowan mechanism to strengthen the matrix.Combined with the tensile curve after hot rolling,it could be judged that the sample had a brittle fracture model after hot rolling.This essentially indicated that the dislocation plugging effect under the Orowan strengthening mechanism after hot rolling was fully exerted,and the tensile properties of composites after hot rolling were more determined by the interface strength of the reinforcement/matrix.Therefore,the tensile strength of the final prepared 1％WC/Cu composite sample reached 407 MPa,and Vickers hardness reached HV 126.6,and the electrical conductivity could still maintain 99.1％IACS.The tensile strength of the final prepared 2％WC/Cu composite sample reached 405 MPa,Vickers hardness reached HV 124.1,and the electrical conductivity could still maintain 99.1％IACS.
WC/Cu matrix compositevacuum hot-pressing sinteringOrowan mechanismhot rolling composite
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