Effect Of Reinforcement Phase Regulation On Microstructure And Properities Of （Ni₂B+C）/Cu Composite

Although the research on copper matrix composites at home and abroad has been increasingly mature and has achieved fruitful scientific research results.However,there are still some problems in the actual production process of the composites prepared by powder metallurgy.such as it’s difficult to control the in-situ reaction process and regulate the reinforcement phase,resulting to the aggravated loss of material conductivity.To solve these problems,in this paper,we used Cu-10wt%Ni alloy powder and B4C powder as raw materials,utilized methods of vibration mixing and hot pressing sintering to prepare fully compact sintered（Ni₂B+C）/Cu composite with great performance,selected the optimal sintering process parameters of composites.Then,the in-situ reaction process was controlled by heat treatment to regulate Ni₂B reinforced phase,and the optimal heat treatment process parameters were determined.It was found that the presence of primary powder boundary would seriously affect the properties of（Ni₂B+C）/Cu composites,and the powder boundary should be eliminated by thermal deformation method.Finally,the processing technology of（Ni₂B+C）/Cu composite was determined to be hot press sintering—solution treatment--multi-direetional forging—aging treatment.Microstructure,conductivity,hardness,strength,friction and wear properties of composites with different processes were observed.Microstructure evolution behavior and its influenee mechanism on the properties of composites during heat treatment and thermal deformation were explored.The regulation of the reinforcement phase size and distribution in the composites was realized,the excellent properties of（Ni₂B+C）/Cu composites were obtained.The main conclusions of this paper were as follows:1.In order to conduct the densification and in-situ reaction process in an orderly mannet,firstly the mixed powder was sintered by hot pressing,and the optimal sintering process of（Ni₂B+C）/Cu composite was determined to be 950℃×1h.In this sintering process,the balance between the in-situ reaction degree in the material and the growth of Cu matrix grains and reinforced particles can be achieved,which laid a foundation for further regulating the size of Ni₂B reinforced phase in the subsequent heat treatment process.2.Microstructure evolution behavior of（Ni₂B+C）/Cu composites during heat treatment can be described as:with the increase of solution temperature and the extension of holding time,the grain boundary expanded outward along with the growth of Cu matrix grains.The worm-like Ni₂B blocks at the powder boundary were gradually annexed into Cu matrix,then Ni₂B blocks and some Ni₂B particles in Cu matrix were solidly dissolved into Cu matrix.Later,during the aging process,more uniform and fine Ni₂B reinforced phase particles were generated in Cu matrix through the in-situ reaction,which can significantly played a role of precipitation strengthening.The optimal heat treatment was 950℃×2h+600℃×4h,and the particle size of Ni₂B can reach 0.91μm.3.The primary powder boundary in（Ni₂B+C）/Cu composite can be eliminated by multidirectional forging process,thus the cracking phenomenon caused by continuous amorphous C phase on the powder boundary can be suppressed,the strength and plasticity of the material can be greatly improved.For the solid-solution state composite after multi-directional forging,thermal deformation in this process can be used to fully promote the precipitation of fine reinforced phase particles during the aging treatment,and the particle size of Ni₂B can reach 0.85μm,so as to further improve the properties of composites.Compared with the sintered（Ni₂B+C）/Cu composite,the conductivity of the post-treated material can reach 46.53%,which was increased by 69.41%;the hardness can reach 171.14HV,which was increased by 55.3%;the tensile strength can reach 355MPa and the elongation can reach 5.2%,both of which have been greatly improved,achieving a breakthrough in material properties,and the material fracture mechanism changed from brittle fracture to remarkable ductile fracture.4.The friction coefficient and mass wear rate of（Ni₂B+C）/Cu composite obtained after hot press sintering—solution treatment—multi-direction forging—aging treatment were significantly reduced compared with the sintered state,the friction and wear performance was improved,because more fine Ni₂B particles in the material played a protective role in supporting Cu matrix.Raman spectroscopic analysis confirmed that C existed in the composites of different states.The graphitization of non-crystalline C in the process of friction and wear was an important reason for the self-lubricating effect of composites.