Mechanical Properties And Oxidation Behaviour Of Tmc(TM=Ta,Nb,Ti,Zr) Ultra-high Temperature Ceramics

Transition metal carbide（TMC）ceramics belong to ultra high temperature ceramics（UHTC）with excellent physicochemical properties such as ultra-hardness,low thermal conductivity and corrosion resistance,and therefore have great potential for use in extreme environments such as aerospace,nuclear and high-speed cutting^[1-3].It has great potential for applications in extreme environments such as aerospace,nuclear and high-speed machining Due to the strong covalent bonding in TMC ceramics,it is difficult to achieve a dense state when sintering at low temperatures,therefore,how to prepare TMC ceramics in an effective and energy-efficient manner is a common research hotspot among scholars at home and abroad.In addition,as the service environment of TMC ceramics continues to become more complex,the study of their high-temperature mechanical properties is also receiving more and more attention.Through high-pressure sintering techniques,we have prepared four TMC ceramics and systematically characterised their phase composition and microstructure to further investigate their mechanical properties and oxidation behaviour,the main research contents and results are as follows:In this study,four dense TMC ceramics relative densities of TaC（99.32%）,NbC（98.94%）,TiC（98.17%）and ZrC（96.41%）were prepared using TaC,NbC,TiC and ZrC powders,which were ball-milled and then sintered by high-pressure sintering at a relatively low temperature of 1500°C and a pressure of 7 GPa,which is lower than most of the other reported reported to densify TMC ceramics at the lowest temperatures.The room temperature nanohardness of TaC ceramics is 19.5±0.3 GPa,NbC ceramics is18.5±0.2 GPa,TiC ceramics is 26.2±0.3 GPa and ZrC ceramics is 20.2±0.4 GPa;their modulus of elasticity is 401.5±9.2 GPa,335.8±11.5 GPa,318.5±15.1 GPa and 291.6±12.3GPa;the hardness and modulus of elasticity showed a linear decrease in hardness and modulus of elasticity at high temperatures.The fracture toughness of the four TMC ceramics was 2.5±0.2 MPa·m^1/2,2.9±0.1 MPa·m^1/2,2.8±0.2 MPa·m^1/2 and 1.8±0.2 MPa·m^1/2respectively,which are similar to the reported relevant mechanical properties,fully confirming the feasibility of high-pressure sintered TMC.The four sintered TMC ceramics were heat treated at 200,400,600,800 and 1000°C for a certain period of time and their oxidation behaviour was investigated by characterising the samples with the aid of TG-DSC,SEM,EDS and profilometer.The results show that their oxidation process is a weight gain process and their oxidation kinetics follows a parabolic law.The oxidation mechanism of these four TMC ceramics can be briefly summarised as follows:at slightly lower heat treatment temperatures,oxidation reactions occur on the surface of the specimens,cracks are generated on the surface due to uneven thermal stress,and as the temperature increases,the oxidation reaction products decompose into gases such as CO,CO2and some by-products are generated,while the TMC comes into contact with oxygen to continue the oxidation reaction,and the generated oxidation products sinter and solidify as the temperature increases The generated oxidation products are sintered and cured as the temperature rises.