Study On The Microstructure And Properties Of Graphene-Diamond Hybrid-Reinforced Copper Matrix Composites

Metal matrix composites have played an indispensable role in the development of human science and technology and social progress.Since the last century,aerospace engineering,military instruments and industrial industries have flourished with the advancement of metal matrix composites.Pure copper is widely used in military defense,electronic devices and electric power systems because of its low density,high electrical conductivity,high thermal conductivity,high corrosion resistance and other properties.But poor strength,low hardness,easy to wear and other shortcomings limit its further application,so the composite metal material is an irreversible trend.Currently,conventional particle and fiber reinforcement can enhance the strength and elastic modulus of metal matrix composites,however this is often accompanied by a significant reduction in material plasticity.For this problem,hybrid reinforcement provides a solution.The so-called hybrid reinforcement,that is,the introduction of two or more reinforcements into the metal matrix,relying on the properties of different reinforcements to strengthen the corresponding properties of the composite,so that the material obtains comprehensive excellent performance.In this thesis,two reinforcements,nano-diamond and graphene,were used to prepare hybrid reinforced copper matrix composites.The main research and conclusions are as follows:（1）The ball milling method was used to achieve uniform dispersion of nano-diamond in copper powder by continuous adjustment of ball milling speed,ball milling time and diamond content,and flaky diamond/copper composite（Dia/Cu）powder of moderate thickness was obtained.For the introduction of graphene,the in-situ growth method was used,and the dispersion of nano-diamond and composite powder in the previous step was well preserved during the in-situ growth,and graphene was uniformly dispersed,and the graphene-diamond/copper（Gr-Dia/Cu）composite powder was successfully prepared.（2）After the preparation of the composite powder was completed,the bulk Gr-Dia/Cu composites were prepared using SPS sintering.The microstructure of the bulk composites was characterized using SEM and EBSD,and it was found that nano-diamond and graphene were uniformly distributed in the copper matrix.Moreover,the distribution along the direction perpendicular to the sintering pressure showed a striped pattern.The grain refinement of the copper matrix occurred after the enhancement by the mixture of graphene and nano-diamond.The grain size of Gr-Dia/Cu composites was reduced by 71%compared with pure copper under the same process,and the grain refinement was superior to that of Dia/Cu composites.Also,the hybrid reinforcement of graphene and nano-diamond was better than the single diamond reinforcement in terms of hardness improvement,which was 55.2%.In the tensile test,the Gr-Dia/Cu composites exhibited a combination of large and small toughness nests with a yield strength of 221 MPa,which was 79.7%higher than that of pure Cu,and the improvement value was about twice that of Dia/Cu.The tensile strength of Gr-Dia/Cu was 306 MPa,which was 30.8%higher than that of pure Cu,and the improvement value was about 1.5 times that of Dia/Cu.The Gr-Dia/Cu composites have significantly increased the strength while reducing the loss of plasticity.（3）Through electrochemical corrosion tests,it was found that the corrosion resistance of the composites was significantly improved after the hybrid enhancement.The corrosion voltage and corrosion current of Gr-Dia/Cu were-98 m V and 3.082×10^-7 A/cm²,respectively.The corrosion rate of Gr-Dia/Cu was as low as 0.0723 mm/year.Compared with pure Cu,the corrosion resistance efficiency was improved by 57.74%.The corrosion products of Gr-Dia/Cu were found to be Cu₂O,Cu（OH）₂ and Cu O using XPS on the surface of the corrosion samples,among which Cu O was relatively high in Gr-Dia/Cu.And according to the literature,it is presumed that the relatively high proportion of Cu O in the corrosion products of Gr-Dia/Cu is converted from Cu₂O under the induction of graphene;and the corrosion resistance of Gr-Dia/Cu under high concentration of chloride ions was further tested by salt spray corrosion.After corrosion morphology observation,surface roughness and weight loss calculation,the comparison results also showed that the corrosion resistance of the hybrid-reinforced composite was greatly improved.