The Indentation Mechanical Properties And High Temperature Oxidation Behavior Of ZrB₂-SiC Ultra-high Temperature Ceramics

ZrB₂-based ultra-high temperature ceramics can maintain their own stability in extreme environments and have a melting point higher than 3000℃.Because of their excellent mechanical properties,high thermal conductivity and good thermal vibration resistance,they are widely used in the protection of ultra-high temperature structures.In this paper,the mechanical properties and high temperature oxidation behavior of ZrB₂-based ultra-high temperature ceramics were studied as follows.（1）The high-density ZrB₂-Si C ultra-high temperature ceramics are prepared by spark plasma sintering.Through density testing,it is found that the relative density of ZrB₂-Si C ultra-high temperature ceramics is as high as 99.1%.Nanoindentation method is used to test its mechanical properties such as hardness and elastic modulus.The test results show that the ZrB₂-based ultra-high temperature ceramics prepared in this article have higher relative density and higher material hardness and elastic modulus.（2）Based on the continuous stiffness method,the influence of the indentation strain rate on the hardness test value of the matrix was studied,and a series of nanoindentation tests were performed on ZrB₂-Si C ceramics at four different strain rates.It was found that the hardness test value of ZrB₂-Si C ceramics showed an increasing trend with the increase of strain rate,showing a significant strain rate correlation,while the elastic modulus had nothing to do with the strain rate.（3）Considering the scale effect phenomenon in the hardness test of ZrB₂-Si C ceramics,this paper uses four models of ER,PSR,MPSR and Nix-Gao to calculate the true hardness H₀of the material.The results show that the calculation result of the Nix-Gao model is closer to the real hardness of the material,and the strain rate sensitivity index after excluding the size effect is significantly lower than the strain rate sensitivity index without considering the size effect.（4）In order to study the oxidation resistance of ZrB₂-Si C in a high-temperature service environment and the mechanical properties of the oxidation products,the substrate was kept at different temperatures for 1 hour.Through the analysis of mass weight gain per unit area,the weight gain rate increases firstly and then decreases with the increase of oxidation temperature.When the temperature is 1400°C,the mass per unit area increases the fastest.Nanoindentation experiments were performed on oxide films prepared at different temperatures.The results showed that the hardness of ZrB₂-Si C ultra-high temperature ceramics under high temperature oxidation environment was significantly lower than that of the matrix,which provided a certain reference for practical engineering applications.