Study On Low Temperature Sintering And Mechanical Properties Of Zirconium Carbide Ceramics

Zirconium carbide（Zr C）has attracted attention for its excellent physical and chemical properties and is widely used in aerospace and advanced nuclear ceramic materials.However,the main chemical bond of Zr C ceramics is covalent and its low diffusion coefficient makes it difficult to be sintered,which makes the conventional sintering of Zr C ceramics require a high sintering temperature（>2000°C）and a certain pressure during the sintering process,which results in high energy consumption,serious environmental pollution,and low automation.In addition,the sintering performance of Zr C ceramics is influenced by the particle size,agglomeration and carbon vacancies of the Zr C ceramic powder.In order to obtain high density and excellent performance of ceramic materials at low sintering temperature,this thesis used polyethyleneimine（PEI）as dispersant and combined with mechanical ball milling method to refine Zr C ceramic powder;B/Si sintering additives were used to improve the sintering performance of Zr C ceramics,and Zr C ceramic composites were prepared by using discharge plasma sintering method.The effect law of dispersant addition on the dispersion of Zr C was studied,the sintering characteristics of Zr C powder under different dispersant addition and sintering temperature were explored,and the mechanism of the effect of B/Si sintering additives on the mechanical properties of Zr C composites was analyzed.The main conclusions of this thesis are as follows.（1）The dispersant PEI can adsorb on the surface of Zr C powder to improve the resistance of particle agglomeration and thus effectively improve the dispersibility of Zr C powder,while the dispersant PEI has a saturation adsorption amount in the Zr C suspension and its protonation degree is affected by the p H value of the dispersion system,so its dispersion effect is best when the dispersion system is strongly acidic（p H=3）and the addition amount is 0.6 wt%,and the dispersion system is more stable.（2）The densities and bending strengths of Zr C ceramics with dispersant added at the sintering temperature of 1600℃were higher than those without dispersant,reaching 96.24%and 287.53 MPa,but the dispersant PEI decomposed at high temperature and produced gas during the sintering process,causing the densities and bending strengths of Zr C ceramics with dispersant added to decrease as the sintering temperature increased.（3）The B/Si sintering additive generates liquid phase and removes oxygen impurities from Zr C powder during the sintering process,which effectively improves the densities of Zr C ceramics to more than 93%,and also reacts with the Zr C matrix to produce B₄Si,Si B₆,Si C and Zr B₂,which hinders the growth of Zr C grains and improves the mechanical properties of Zr C ceramics.（4）When the sintering temperature was 1800℃,the addition of B/Si sintering aid was5 wt%,and the mass ratio of added B to Si was 1:1,the densities of Zr C ceramics with B/Si sintering aid were 96.31%higher than those of the initial Zr C ceramics and the best overall mechanical properties,mainly the bending strength of 776.63 MPa,the hardness of 22.7796GPa,and the fracture toughness of 6.1576 MPa?m^1/2.