Preparation,Microstructure And Properties Of B₄C-TiB₂-SiC-(BN)Composite Ceramics

Boron carbide(B4C)has many excellent physical and chemical properties,including low density,high hardness,high melting point,high elastic modulus,good chemical stability,and excellent neutron absorption properties.Due to the above excellent properties,boron carbide ceramics are widely used in bulletproof armor,cutting tools,wear-resistant parts,and nuclear powder engineering,it is considered as an important structural functional ceramic material.However,boron carbide ceramic materials also have some disadvantages which cannot be ignored.On the one hand,the densification of sintering is very difficult and the sintering temperature is very demanding.On the other hand,its fracture toughness is very low,only 2?3 MPa?m^1/2.The above defects seriously hinder the further wide application of boron carbide ceramic materials.This project is based on solving the above defects of B4C ceramics.Various experiments on strengthening and toughening of the ceramics were designed.The preparation process of B4C composite ceramics was explored,and the microstructure,mechanical properties,and toughening mechanism of B4C composite ceramics were studied.It provides technical support and theoretical basis for the application of high performance multifunctional B4C matrix composite ceramics.1.Effects of TiB₂ and SiC on the microstructure and properties of B₄C-TiB₂-SiC composite ceramicsThe rigid second phase particles TiB2 and SiC were introduced to strengthen and toughen the B4C ceramics,the suitable amount of TiB2 and SiC were also explored.B4C-TiB2 binary composite ceramics with TiB2 content of 10,20,30,and 40 vol%were prepared by hot-pressing sintering with B4C and TiB2 powders as raw materials.The microstructure,mechanical properties,and electrical conductivity of the composite ceramics with different TiB2 contents were compared and studied,and the optimal TiB2 content in B4C-TiB2 binary system was determined to be 30 vol%.On this basis,B4C-TiB2-SiC ternary composite ceramics with SiC content of 0,10,and20 vol%were prepared by hot-pressing sintering with B4C,TiB2,and SiC powders as raw materials.The influence of SiC content on the microstructure and mechanical properties of the material and the influence of SiC on the antioxidant properties of the material were studied,and the optimal introduction amount of SiC was determined to be 10 vol%.2.B₄C-TiB₂-SiC composite ceramics prepared by ball milling combined with hot pressing sinteringIn order to overcome the adverse effects of the coarse particle size of commercial powders,the B4C-TiB2-SiC composite powders were refined by using different time ball milling processes.The particle size distribution,specific surface area,oxygen content,and wear rate of SiC pellets were studied,and the characteristics of ball milling process in different stages were analyzed.Then,B4C-TiB2-SiC composite ceramics were prepared by hot-pressing sintering.Through comparion and analysis of the densification behavior of the composite powders with different milling time,the activation effect of the ball milling composite powders was further proved,and the mechanism of promoting sintering in the densification process of the composite powders was explored.The microstructure and mechanical properties of the B4C-TiB2-SiC composite ceramics with different milling time were studied.The results show that the mechanical properties and microstructure of the composite ceramic samples prepared by hot-pressing sintering are improved and optimized compared with those prepared by non-ball milling.The relative density,hardness,bending strength,and fracture toughness of the B4C-TiB2-SiC composite ceramics prepared by ball milling process combined with hot-pressing sintering reached 99.20%,32.84 GPa,858 MPa,and 8.21 MPa·m^1/2,respectively.Finally,the toughening mechanism of the composite ceramics is discussed in combination with the microstructure and crack growth path.3.B_xC-TiB₂-SiC composite ceramics prepared by in situ reactive hot pressingBall milling process can effectively refine commercial powders,but the ball milling process consumes a lot of time,and complicated preparation process of the ceramic composites.In order to simplify the preparation process of B4C-TiB2-SiC ceramic composites,composite powders with small particle size were obtained through in-situ reaction,and the interfaces of the ceramic composites were optimized.Bx C-TiB2-SiC composite ceramic materials were prepared from Ti C,B,and Si powders by in situ reactive hot-pressing sintering.The chemical reaction process of the composite powders during sintering process was studied by heating them to different temperatures for heat treatment and X-ray diffraction analysis.The stoichiometric ratio of B and C in boron carbide is variable.In this experiment,composite ceramics containing different degrees of excess B(0,10,20,and 30 wt%B)were prepared,and the influence of B content on the microstructure and mechanical properties of the composite ceramics was investigated.The results showed that the B6.1C-TiB2-SiC composite ceramics prepared from the composite powder containing 30 wt%excess B had the best comprehensive mechanical properties,with the relative density,hardness,bending strength,and fracture toughness of 98.32%,33.2 GPa,840 MPa,and 5.22 MPa·m^1/2,respectively.Finally,the forming process of Bx C(x>4)with boron rich phase was analyzed,and the strengthening and toughening mechanism of Bx C-TiB2-SiC composite ceramics was discussed.4.B_6.5C-TiB₂-SiC-BN composite ceramics prepared by in situ reactive hot pressingBy introducing BN to improve the fracture toughness and mechanical damage resistance of the ceramic composites,the purpose of preparing multifunctional boron carbide ceramic composites with excellent comprehensive performance was realized.B6.5C-TiB2-SiC-BN composite ceramic materials were prepared from Ti CN,B,and Si powders by in situ reactive hot pressing sintering,and the chemical reaction process of the composite powder during sintering process was studied by heating it to different temperature.A novel core-shell structure of the B4C-TiB2-SiC-BN composite powders was synthesized by in-situ reaction,which promoted the densification process during the sintering process of the composite powders.B6.5C-TiB2-SiC-BN composite ceramic samples prepared through in-situ reactive hot-pressing sintering showed a high relative density(98.8%),and excellent comprehensive mechanical properties,with hardness,bending strength,and fracture toughness reaching 19.6 GPa,801 MPa,and 5.31 MPa·m^1/2,respectively.Finally,anisotropy and toughening mechanism of B6.5C-TiB2-SiC-BN composite ceramics were studied.