| Copper and its alloys have been widely used in daily life since their excellent properties,but the low strength,hardness and poor wear resistance seriously limit their application in industry domains.In order to improve the strength and wear resistance of copper on the basis of maintaining their excellent electrical and thermal conductivities and machinability,it is a popular way to add some fibers,whiskers or granular reinforcements into Cu matrix to form composites.In this paper,(Ni2B+C)/Cu composites were prepared by hot pressing sintering and hot extrusion from Cu-Ni and B4C powder system,where strengthening phase Ni2B and self-lubricating phase C were simultaneously introduced into the copper matrix by in-situ reaction from Ni and B4C.Electrical conductivity,hardness and density of the composites were tested by eddy current conductometer,Vickers hardness tester and Archimedes drainage method.Friction and wear properties of the composites at room temperature were evaluated by HT-1000 friction and wear tester.Microstructure,phase composition and morphologies of worn surface of the composites were investigated by scanning electron microscopy,X-ray diffraction,transmission electron microscopy equipped with energy dispersive spectrometer.Diffusion and in-situ reaction behavior was studied by diffusion couple experiment and kinetic analysis.The main conclusions are as follows:(1)With the increase of sintering temperature and time,the density of composites increases continuously,but the hardness and electrical conductivity increases first and then decreases.Based on this,the optimum sintering temperature 900? and holding time 1.5 h can be obtained.When the sintering temperature is low,B4C can not fully react with Cu-Ni matrix,but both the grain of matrix and product N2B start to coarsen,resulting in the decrease of both hardness and electrical conductivity.(2)XRD and EPMA analysis of Cu-Ni/B4C diffusion reaction couple samples prepared by vacuum hot-pressing sintering of Cu-Ni alloy powder and B4C bulk were carried out,and the results show Ni atoms dis-solute from Cu-Ni alloy and react with B4C powder to from Ni2B and C.The content of Ni2B and C in the composites could be regulated by adjusting the amount of Ni element.The products Ni2B and C phases are uniformly distributed in the matrix.(3)With the increase of sintering temperature and holding time,the thickness of the diffusion and reaction layer increases obviously.The growth of reaction layer is interface-controlled,and the growth constant yield to the Arrhenius formula.Growth rate constant is k=3.45×107 exp(-137.32×103/RT),Activation energy of the in-situ reaction is Q=137.32kJ·mol-1,and thus the growth kinetics equation can be expressed as?=3.45 ×107exp(-137.32×103/RT)t0.9.(4)The in-situ reaction products Ni2B and C can significantly strengthen the Cu matrix.When the content of Ni is 10%,the tensile strength of(Ni2B+C)/Cu composite is the highest,which is 355.55 MPa and increases by 30.10%compared with pure copper.On the other hand,although the elongation of the composites is the lowest when the content of Ni is 10%,it also reaches 13.10%,which can meet the requirement of structural materials used in engineering applications.(5)The wear resistance of(Ni2B+C)/Cu composites is obviously higher than that of pure copper,suggesting that the in-situ reaction product C can improve the wear performance.Under dry friction and wear conditions,the wear mechanism of copper is adhesive wear,but that of(Ni2B+C)/Cu composite is abrasive wear.With the increase of load,the friction coefficient decreases but the wear rate increases. |
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