Research On Carbon Quantum Dots Reinforced Copper Matrix Composites

In copper matrix composite materials,due to the poor wettability between reinforcements(carbon nanotubes,graphene)and copper matrix,it is very easy to cause agglomeration phenomenon due to the inability to uniformly disperse,resulting the poor interfacial bonding ability.The mechanical strengthening effect of the copper matrix composite materials is not obvious or causes greater defects,which obviously fails to meet the initial experimental design requirements.Not only that,the weak bonding interface forms an electronic barrier and electron scattering,which seriously affects the electrical properties of copper matrix composite materials.Although researchers have been developing new processes to improve these problems of carbon nanomaterials in the metal matrix,they have not been able to fundamentally solve these problems.To this end,this article explores the possibility of a new carbon nanomaterial to enhance copper matrix composites,and conducts a certain analysis and research on the microstructure and phase composition of the new carbon nanomaterial—carbon quantum dots(CQD);With CQD as the reinforcement,the preparation,interface structure,performance and reinforcement mechanism of CQD/Cu composites and CQD/Cu-Ti alloy composites were studied.Experimental results show:(1)The CQD with citric acid and ethylenediamine as precursors was successfully prepared by one-step hydrothermal method,and its particle size was about 0.24 nm;it showed long-term uniformity at room temperature without obvious polymerization precipitation.It was found that the Phase analysis and microscopic characterization of CQD mainly composed of sp² hybrid carbon atoms,and there are various hydrophilic functional groups(such as hydroxyl,amino,and carboxyl)on the surface.This enables CQD to provide binding sites during the compounding process with copper-matrix powders,which makes these groups easily chemical react with copper to form Cu-O-C bonds and solve the problem of poor wettability between carbon and copper matrix.With the gradual increase of the hydrothermal reaction temperature,the oxygen-containing functional groups gradually decompose,the polymer-like carbon dots are carbonized,the CQD lattice constant becomes larger,and the crystalline carbon content increases.In the subsequent process of combining with the Cu-Ti alloy,which is easier to generate the second phase product-carbide,and the interface bonding strength of the copper-based composite material was improved by establishing a new interface,so that its mechanical properties can be improved.(2)The CQD/Cu₂O composite powder was prepared by the molecular-level mixing method.The CQD was evenly divided in the copper matrix and formed a chemical bond Cu-O-C to firmly bond the CQD and the copper matrix together,which effectively improves the interface binding capacity,and formed a semi-coherent interface.The study found that the ultimate tensile strength(UTS)and yield strength(YS)of CQD reinforced copper matrix composites are greatly improved.When the CQD content is 0.4wt.%,the UTS of CQD/Cu composites is 271 MPa,which is about 31%higher than the pure copper sample prepared by the same method;the conductivity reaches 94.8 IACS%,which is very closed to the conductivity of the pure copper prepared by the same conditions(96.6IACS%).The UTS and YS of CQD/Cu-Ti alloy composite materials reached 407 MPa and 350 MPa,respectively.When the CQD content is 0.2 wt.%,the composite material shows a good elongation,which is much higher than other composite materials with mass fraction CQD.Among them,the elongation rate of the 0.2 wt.%CQD/Cu composite is37.3%;The elongation of 0.2 wt.%CQD/Cu-Ti alloy composite is 34.9%,which is 2.3times higher than that of pure Cu/Cu-Ti alloy composite.(3)Through the analysis of the strengthening mechanism of CQD reinforced copper matrix composites,it is found that when the CQD mass fraction is less than or equal to0.2 wt.%,less Ti C is generated in the CQD/Cu-Ti alloy composites,and the strengthening mechanism is as good as CQD/Cu composite material is similar,mainly through the covalent bond between copper and carbon atoms.The Cu-O-C bond enhances the bonding between carbon and metal,which improves the bonding strength and load transfer capacity of the interface between the copper matrix and carbon.And the synergistic effect of crystal strengthening makes the mechanical properties of CQD/Cu composites significantly improved,and its elongation is the most obvious.When the mass fraction of CQD>0.2 wt.%,CQD reacts with Cu-Ti alloy to generate a large amount of Ti C.Through the study of the evolution mechanism of carbides,fine grain strengthening,dislocation strengthening,and Orowan strengthening are the main strengthening mechanisms of CQD/Cu-Ti alloy composites.And the contribution of these three-strengthening mechanism to the UTS was obtained by theoretical calculated:10.4.MPa,42.8 MPa and 53.7 MPa,which is closer to the actual value.