Effect Of Component On Phase Composition And Mechanical Properties Of High Entropy Carbide Ceramics

Transition metal carbide ceramics are promising in the fields of aerospace,nuclear energy and machining due to high hardness,elastic modulus,excellent heat shock resistance,chemical corrosion resistance and friction and wear resistance.With the increasing requirements in related fields,the properties of single component transition metal carbide can not satisfy the demand of engineering application,so the emergence of high entropy transition metal carbide ceramics has attracted the attention of scientific researchers.The four typical effects of high entropy materials and the designability make it have higher hardness,lower thermal conductivity,excellent oxidation resistance and corrosion resistance.It is considered to be a great potential of ultra-high temperature structural material.However,the diversity of high entropy ceramic component design complicates the research on the relationship between material preparation,phase composition,microstructure.Based on the previous study of equal ratio high entropy carbide(Ti_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2)C by our research group,this work will focus on ternary and quaternary carbides.Firstly,ternary and quaternary transition metal carbide powders were prepared by transition metal oxides and carbon black,and then carbide ceramic blocks were prepared by spark plasma sintering（SPS）.The relationship between the component,phase composition,microstructure and mechanical properties of high entropy carbide powders and ceramics was studied,and its internal mechanism was analyzed.The main research contents and results of this paper are as follows:Firstly,three to four components were selected from Ti O₂,Zr O₂,Hf₂O₅,Nb₂O₅ and Ta₂O₅.Multi-component carbide powders were synthesized from these transition metal oxides and carbon black by carbon thermal reduction process under 1600°C for 1 h.The phase formation laws of the powders are as follows:a)It is easier to obtain single-phase powders by removing Zr C and Hf C,or removing Nb C and Ta C at the same time;b)The two phases of high entropy carbide powders are based on the crystal structure of Hf C and Ta C respectively,and other components tend to be dissolved into the matrix phase;c)Ti C can expand the difference of lattice constants between the two phases in the powders,making the solid solution of the two phases more difficult.Secondly,ternary and quaternary carbide ceramics were prepared from self-synthesized powders by SPS under 1900°C for 10 minutes.The relationship between their components,phase composition and microstructure were analyzed.The results show that both ternary and quaternary carbide ceramics have single-phase face centered cubic structure,and their relative densities are more than 97.27%.The distribution of transition metal elements in the matrix phase of high entropy carbide ceramics is uniform and the content is close to equimolar.In addition to the matrix phase,there is carbon black phase that did not participate in the reaction.The content of carbon black phase increases with the increase of the content of IVB group transition metal carbides in the component.Thirdly,the mechanical properties of ceramics are affected by composition,content of carbon black,grain size and so on.By controlling the component to optimize the microstructure and properties of the materials,the quaternary carbide(Ti_0.25Hf_0.25Nb_0.25Ta_0.25)C obtains excellent mechanical properties.Its Vickers hardness reaches 21.72±0.60 GPA and Young’s modulus reaches499 GPa.