Property Prediction And Micromechnical Finite Element Simulation Of Yb₂Si₂O₇/MoSi₂ Composite Ceramics

SiC-based composites are considered to be ideal materials for the next generation of gas turbine blades or hot end components.In order to prevent the decline of SiC-based composite materials in the rapid combustion environment,the researchers successfully used environmental barrier coatings?EBCs?.However,even the APS coating technology still cannot help the coating completely avoid the cracks generated during the deposition process,thermal cycling or foreign object impact.If it can repair the cracks in the coating during the thermal cycle,it will be a breakthrough in the development and application of EBCs.Therefore,this subject decided to add self-healing enhancement particles MoSi₂ into Yb₂Si₂O7,an excellent surface candidate material,to prepare Yb₂Si₂O₇/MoSi₂ multiphase ceramics.At the same time,the study of the performance of traditional ceramic materials mainly relies on macro-scale testing and qualitative analysis of microstructure characteristics,but lacks direct research on its micromechanical properties.Therefore,this subject decided to study the preparation and micromechanical behavior of Yb₂Si₂O₇/MoSi₂ composite ceramics.After calcining Yb₂O₃+2.4SiO₂ at 1500? for 4h,pure phase Yb₂Si₂O7 powder can be obtained.Two-phase unreacted Yb₂Si₂O₇/MoSi₂ multiphase ceramics were obtained by vacuum hot pressing sintering at 1550? and 30 MPa.With the increase of MoSi₂ content,the density of Yb₂Si₂O₇/MoSi₂ multiphase ceramics shows a decreasing trend.Based on the first principle,the material studio software was used to calculate the second-order elastic constants and elasticmodulus of Yb₂Si₂O7 and MoSi₂.Using ANSYS,the overall strain distribution and thermal stress of the multiphase ceramics after sintering and cooling are calculated.The maximum deformation is 1.39×10-2mm,and the average stress is tens of 51-68 MPa.ABAQUS was used to calculate the thermal mismatch stress between the second phase particles between the matrix after sinter cooling and oxidation.The maximum thermal mismatch stress after sinter cooling was 0.84 GPa,and the maximum thermal mismatch stress after oxidation was 0.47 GPa,both in the matrix.These are allunder the directional tensile strength of the material.The uniaxial compression model of Yb₂Si₂O₇/MoSi₂ composite ceramics was constructed using finite element simulation technology.The effects of different microstructure interface orientations,microstructures such as second-phase particles and pores on the stress-strain state of composite ceramics were studied.The results show that the iso-stress structure at the horizontal interface is controlled by the strain of the soft phase and produces strain non-uniformity.The yield strength is 2.85 GPa.In the equal strain structure of the vertical interface,the two-phase deformation restricts each other to produce stress non-uniformity,and the yield strength is 6.70 GPa.When the second-phase particles and pores are stressed,a stress concentration effect will occur near the substrate,which can induce new micro-cracks,leading to crack propagation and material failure.The Yb₂Si₂O₇/MoSi₂ composite ceramics micro-fracture model was establishedby finite element method.The study of sharp crack models with different geometric states showed that increasing the crack opening angle would increase the stress intensity,but would reduce the stress field intensity factor and increase the crack tip radius of curvature.The effect is opposite to this.The crack depth has a synchronous effect on the stress intensity and stress field intensity factor.The stress intensity increases rapidly with the crack depth.When the crack depth is 0.8?m,it reaches 1.86 GPa and 0.98 MPa·m1/2,respectively.By embedding the cohesive cohesive element,the simulation of the crack propagation path of Yb₂Si₂O₇/MoSi₂ composite ceramics was preliminarily created.