Research On Synthesis Mechanism Of Ternary Layered Ceramics（V₂SnC,Ta₄AlC₃） And In Situ V₂C-reinforced Cu（Sn） Composite

M_n+1AX_n phases,which including metal bonds and covalent bonds in crystal structure,possess properties of metal and ceramic,such as good electrical and thermal conductivity,high Young’s modulus,and high strength.Due to weakly bonding of A atoms in M_n+1AX_nphases,they are easily to be precipitated under certain conditions.Then layered MX phases are retained.For M_n+1AX_n phases and MX phases own self-lubrication,low hardness,and good electrical conductivity,they are suitable to be reinforcements for metal matrix composites.Introducing M_n+1AX_n phases and MX phases to metal matrix can overcome the problems introduced by traditional ceramics,such as extremally high hardness,low electrical conductivity,and poor compatibility between reinforcements and matrix.This paper focused on M_n+1AX_n phases（V₂SnC and Ta₄AlC₃）and Cu based composites prepared by V₂SnC and copper.By optimizing sintering temperature,holding time,and molar ratio of C when preparing V₂SnC,VC_0.75 finally be removed.And by adjusting sintering temperature and molar ratio of raw powders while preparing Ta₄AlC₃,synthesis mechanism ofα-Ta₄AlC₃ andβ-Ta₄AlC₃ was figured out.Then V₂C/Cu（Sn）composites were prepared using V₂SnC and Cu as raw powders by hot-press sintering.Meanwhile,phase compositions,microstructure,physical and mechanical properties of V₂C/Cu（Sn）composites were researched.The results of this paper were as follows:1.By researching the synthesis mechanism of V₂SnC,we concluded that with the molar ratio of 2/1.1/0.8,purer V₂SnC with no VC_0.75 can be synthesized using tube furnace under Ar atmosphere at 950℃for 3 h.2.When sintering Ta,Al,and C powder mixtures with molar ratios of 4/1.2/2.6,4/1.4/2.6,and 4/2.0/2.6 in a tube furnace range from 1450℃to 1600℃under Ar atmosphere,the reaction path ofα-Ta₄AlC₃ andβ-Ta₄AlC₃ were researched.And no phase transformation would undergo fromα-Ta₄AlC₃toβ-Ta₄AlC₃norβ-Ta₄AlC₃toα-Ta₄AlC₃at1600°C.3.By systematically adjusting the molar ratio of Al from 1.2 to 2.0,all samples sintered at 1600°C confirmed that Al content had little effect on synthesis ofα-Ta₄AlC₃.However,the content ofβ-Ta₄AlC₃ reduced corresponding to raising of Al.4.By sintering V₂SnC and Cu mixture powders using hot press at 750℃under 25 MPa for 1 h,V₂C/Cu（Sn）composites were successfully fabricated.The design and fabrication of MX reinforced Cu based composites was enriched.5.For Sn atoms solid solution into the lattice structure of Cu,the lattice constant of Cu matrix increased from 3.6001（?）（pure Cu）to 3.7192（?）（30 vol.%V₂C）.6.The results of optical microscope showed that introducing V₂C can obviously refined the grains of Cu matrix.The SEM results of tensile fracture showed that V₂C（5vol.%）/Cu（Sn）composite had good plasticity,and severe plastic deformation occurred during the tensile process to form many dimples and ridges.7.The electrical conductivity of V₂C/Cu（Sn）composites reduced from 0.589×108S·m^-1（pure Cu）to 0.034×108 S·m^-1（30 vol.%V₂C）.And the thermal conductivity of V₂C/Cu（Sn）composites reduced from 384.36 W·K^-1·m^-1（pure Cu）to 24.65 W·K^-1·m^-1（30vol.%V₂C）.Though electrical conductivity of V₂C/Cu（Sn）composites reduced because of introducing V₂C,the value of electrical conductivity still higher than Cu based composites reinforced by traditional ceramics.8.Vickers hardness of V₂C/Cu（Sn）composites with 30 vol.%V₂C was 334 HV,which was nearly six times of pure Cu.The tensile strength of V₂C/Cu（Sn）composites with 20 vol.%V₂C achieved highest value（440 MPa）.Comparing electrical conductivity and tensile strength of V₂C/Cu（Sn）composites with Ti C_x/Cu composites,the composites prepared in this paper achieved higher tensile strength while retaining good electrical conductivity.