Reaction Behavior And Process Optimization Of Composites Based On Cu-Ni/SiC System

The trade-off between electrical conductivity,strength and wear resistance is one of the hottest research topics in Cu alloys and composites,which has a large potential in the domains of electric and electron,instruments and apparatus along with rain traffic.In this investigation,based on the Cu-Ni/SiC mixed system,the(NixSi+C)/Cu composites with high strength,high electrical conductivity and good wear resistance are in-situ synthesized by the formation strengthening phase Ni-Si compounds and self-lubricating phase C in Cu materials.First of all,the solid-state phase transformation behavior of Cu-Ni/SiC system is studied by isothermal quenching,which provides theoretical basis for powder metallurgy preparation process;Secondly,orthogonal experiments are used to investigate the effect of three process factors such as mixing method,sintering temperature,holding time,on the structure and properties of(NixSi+C)/Cu composites.So,the powder metallurgy process for preparing Cu matrix composites based on Cu-Ni/SiC system is determined.Then,by studying the microstructure,phase composition,relative density,electrical conductivity and hardness of the samples with different alloy compositions,the best Ni/Si ratios for the(NixSi+C)/Cu composites with high electrical conductivity and strength can be determined.Finally,the solid solution and aging treatment of(NixSi+C)/Cu composites are carried out to study the effects of heat treatment on the structures and properties of the composites.The main conclusions obtains from above investigations are as follows:1.The solid-state reaction behavior of Cu-Ni/SiC mixed system is as follows:at 600℃,δ-Ni2Si phase begins to precipitate at the grain boundary inside the α-Cu(Ni,Si)particles;At 700℃,Ni3Si phase starts to form at the powder boundary,at the same time,the number and size of δ-Ni2Si phase precipitated inside α-Cu(Ni,Si)particles increases obviously.With the further increase of temperature,the δ-Ni2Si phase inside α-Cu(Ni,Si)particles begin to decompose,and when the temperature increases to 900℃,it is completely decomposed.When the temperature is further increased to 950℃,the Ni3Si on the powder boundary merge and grow into a dense block,and the reaction product C was squeezed out to its boundary.2.The precipitation behavior of Ni-Si compounds in the matrix of Cu-Ni solid solution and the reaction behavior between Ni atoms and SiC on the powder boundary are calculated by thermo-kinetic method.It turns out that the Gibbs free energy of the reaction producing Ni3Si at these two sites is more negative than that producing Ni2Si.However,due to the formation of Ni2Si in the solid solution matrix,the corresponding Ni atomic kinetic threshold activity is less than Ni3Si.The precipitation phase in the final solid solution matrix is Ni2Si,and the reaction product on the edge of the particles is Ni3Si.3.The composites prepared by the Cu-Ni/SiC system are composed of α-Cu(Ni,Si)solid solution matrix and its dispersed δ-Ni2Si precipitates and a mixture of Ni3Si and C on the powder boundary,where Ni3Si is the product of the in-situ reaction of Ni and SiC and δ-Ni2Si is the precipitated phase of supersaturated α-Cu(Ni,Si)solid solution during the cooling process.4.The best powder metallurgy process parameters of the Cu-Ni/SiC mixed system are as follows:the mixing powder was vibrated and the pellet ratio is 1:5,the sintering temperature is 950℃,and the sintering time is 2h.Too low mixing energy leads to the non-uniform dispersion of SiC,and there are unreacted SiC particles at the powder boundary in the composites prepared after reaction;Too high mixing energy causes the powder to be seriously deformed,which increases the diffusion of elements in the sintering process,and the mixture of Ni3Si and C at the powder boundary in the composites prepared after reaction presents a network structure;The increase of the sintering temperature and the extension of sintering time cause the increase of the amount of Ni3Si precipitated at the powder boundary of the prepared composites and the density of the materials.In addition,the electrical conductivity and hardness show an increased trend.5.Both Cu content and Ni/Si ratio can significantly affect the strength and electrical conductivity of the composites.For the three kinds of(NixSi+C)/Cu composites with different Cu contents,the conductivity,hardness and comprehensive property as a whole first increase and then decrease with increase of Ni/Si ratio.For the(NixSi+C)/Cu composites with Cu content of 90wt%,the overall performance reaches the maximum when the Ni/Si atomic ratio is 2.2:1.For the(NixSi+C)/Cu composite with Cu content of 95wt%,the comprehensive performance reaches the maximum when the Ni/Si atomic ratio is 2.5:1.For the(NixSi+C)/Cu composite with Cu content of 98wt%,the overall performance reaches the maximun when the Ni/Si atomic ratio is 2.7:1.6.After solid solution and aging treatment,the hardness,electrical conductivity and relative density of(NixSi+C)/Cu composites are significantly lower than those of sintered samples,and the lower the content of Cu,the greater the degree of reduction.Microstructure analysis shows that a large number of holes appear on the surface of the materials after heat treatment,which may be derived from the formation of CO2 during the treatment process.Therefore,(NixSi+C)/Cu materials prepared by powder metallurgy method are not suitable for heat treatment.