Surface Metallization Of Carbon Fiber And Copper Matrix And Titanium Matrix Composites

Carbon fiber(CF)has high axial strength,low,light weight,high fracture strength,high tensile modulus,good conductivity,and low thermal expansion coefficient.For these reasons,the CFs are often used as the reinforcement agents in synthesis of metal matrix composites.As-received and untreated CFs normally have relatively smooth surfaces,low surface energy,low reactivity,lack of chemically active functional groups,poor chemical stability with certain metals such as iron,poor interfacial wettability and poor interfacial adhesion,all of which significantly affect the mechanical properties of composites and restrict their wide-range applications.Therefore,it is critical to modify the surfaces of the CFs to solve the above problems.Coating the surfaces of CFs with a metallic layer is one of the potential solutions.In order to improve the poor interface wettability between carbon fiber and copper matrix,the interface reaction between carbon fiber and titanium matrix occurs.In this paper,firstly,nickel and copper were plated on the surface of carbon fiber by electroplating and electroless plating,and the phase,morphology and interface combination of the coating were characterized.The surface wettability and tensile properties of carbon fibers under different treatment conditions were studied.The fracture mechanism of carbon fibers coated with metal was proposed.CFs reinforced Cu matrix and Ti matrix composites were prepared by adding uncoated CFs and Ni-coated CFs to Cu matrix and Ti matrix through cold pressing sintering and spark plasma sintering(SPS).The distribution state and interface combination of carbon fiber in metal matrix(including Cu matrix and Ti matrix)before and after nickel coating were characterized.The effects CFs and Ni-coated CFs on the density,hardness,conductivity and tensile properties of copper and titanium matrix composites were studied.The results show that:(1)Copper and nickel can be plated on the surface of carbon fiber by chemical plating and electroplating.The coating is uniform,continuous,crystal copper,crystal nickel,well bonded with the CFs.(2)The wettability of Ni-coated CFs and Cu-coated CFs was improved by a dip coating method.The tensile strength of single carbon fiber decreased after degumming,coarsening and metal plating.The breaking elongation of the CFs coated with the Ni layer was increased by 23.4%,though their average fracture strength was slightly decreased from 3.5 GPa to 2.25 GPa.The breaking elongation of the CFs coated with the Cu layer was decreased by 4.2%,though their average fracture strength was slightly decreased from 3.5 GPa to 1.15 GPa.The fracture mechanisms of the Ni-coated CFs during tensile tests are summarized as follows:crack generation between the coating layer and fiber due to existence of residual stress and local stress concentration;coating delamination;and brittle fracture of fiber.(3)The surface metallized carbon fiber and metal powder(Cu powder and Ti powder)are easy to mix evenly and have less agglomeration.3.4 vt.%Ni-coated CFs/Cu composites was sintered by traditional cold pressing(pressing pressure 300 MPa,temperature 900?,time 120 min).CFs and Cu matrix are closely combined,Cu and Ni have diffusion phenomenon,and CFs is evenly distributed.The density,tensile strength,conductivity,hardness were 89.2%,150 MPa,60.5%IACS,and 90.1 HV.However,3.4 vt.%Ni-coated CFs/Cu composites was sintered at 800? for 10 min,and the pressure was 30 MPa by SPS.CFs and Cu matrix were closely bonded.No diffusion phenomenon was found between Cu and Ni.The distribution of carbon fiber was uniform,the density was 98.1%,the tensile strength was 182 MPa,the conductivity was 72.9%IACS,and the hardness was 130 HV.(4)1.7 vt.%Ni-coated CFs/Ti composite was sintered at 1200? for 120 min after being cold pressed at 500 MPa.CFs/Ti matrix are closely bonded,and there is a transition layer of about 2.5 ?m.Howeve,Ti and CF all form TiC in the uncoated CF/Ti composite.The density of the composite is 93.5%,the tensile strength is 230 MPa,and the hardness is 245 HV.However,1.7 vt.%Ni-coated CFs/Ti composite sintered at 1100? for 10 min and pressure of 30MPa was obtained by SPS sintering.The combination of CFs and Ti matrix is closer,the transition layer is thinner,the distribution of carbon fiber is uniform,the density is 97.9%,the tensile strength is 740 MPa,and the hardness is 495 HV.The Nil layer effectively inhibited the diffusion of Ti to CFs,and the thickness of the transition layer was only 2?m.