Low Temperature Preparation And Microstructure Regulating Of (Zr,Ti)(C,N)-SiC Solid Solution Ceramics

The renewal of the nuclear energy system has put forward higher requirements for developing nuclear materials,making the development of new nuclear materials with high-temperature resistance,irradiation/corrosion resistance,and high reliability imminent.With high melting point,good thermal conductivity,low neutron absorption cross-section,and excellent resistance to fission product impact,ZrC ceramic show great potential for development in next-generation nuclear energy systems.However,the sintering performance of ZrC ceramics is very poor,and the high sintering temperature will coarsen the grains and thus reduce their mechanical properties,limiting their application scope.To address these problems,this paper proposes introducing TiC_0.5N_0.5 and Si into the ZrC matrix and preparing single/complex phase solid solution ceramics by controlling the ratio of ZrC to TiC_0.5N_0.5 in the system and using reactive hot pressing sintering at 1500～1700℃.The effect of Si addition on solid solution ceramics’microstructure and mechanical properties was also investigated.In order to prepare single-phase（Zr,Ti）（C,N）solid solution ceramics at lower temperatures,the molar ratio of ZrC to TiC_0.5N_0.5in the system was set to 95:5,and Si was added at 0 mol%,5 mol%,10 mol%,and 20 mol%on this basis.As the addition of Si was 5 mol%,the reaction transformed Si entirely into SiC.The grain refinement by SiC and strengthening by solid solution increased the flexural strength of Z5T5S ceramics by 67%to 522±20 MPa compared with pure ZrC ceramics.When the addition of Si was increased to 10 mol%,the high-temperature phaseβ-Zr Si stabilized by Ti appeared,significantly reducing the ceramics’flexural strength.In contrast,the ceramics’hardness and fracture toughness monotonically rose with the increased Si addition.Compared to the initial composition of single-phase solid solution ceramics,the molar ratio of ZrC to TiC_0.5N_0.5 in complex-phase solid solution ceramics is 50:50,with the same amount of Si added.Due to the increased TiC_0.5N_0.5 content and lower sintering temperature,（Zr,Ti）（C,N）and（Ti,Zr）（C,N）solid solutions appear in the ceramics and are dominated by the former.The reaction and solid solution-driven interdiffusion promote densification,resulting in a relative density of over 99%for the prepared ceramics.The reaction products of SiC andβ-Zr Si follow the same pattern as in single-phase solid solution ceramics.Attribute to SiC and（Ti,Zr）（C,N）solid solution to inhibit grain overgrowth,combined with the strengthening effect of solid solution,the Z50T5S ceramics have excellent combination properties with flexural strength,hardness,and fracture toughness of 508±33 MPa,24.5±0.7 GPa,and 3.8±0.1 MPa·m^1/2,respectively.In addition,the ceramic toughness increases,and the hardness decreases with increasing Si addition.