Preparation And Characterization Of Fiber Monolithic Zirconium Boride Ceramics

As a typical ultra-high temperature ceramic,ZrB₂ ceramic had the advantages of low density,high strength and high thermal conductivity,and became a potential application material for thermal protection system of aerospace vehicles.However,the brittle fracture of ceramic materials limited its application.Because of the unique layered microstructure and dimensional ability of fiber monolithic structure,it had become an effective way to toughen ceramic materials.However,the traditional process was complicated and difficult,and the interface layer was prone to gradient distribution.In order to simplify the preparation process and improved the interface uniformity.In this experiment,the fiber monolithic ZrB₂ ceramics with Si C_w as the cell interface layer（named as FZS_w）and the fiber monolithic ZrB₂ ceramics with BN as the cell interface layer（named as FZB）were prepared by co-extrusion method,and their mechanical properties and oxidative ablation behavior were studied.The co extrusion molding process parameters of fiber monolithic ZrB₂ ceramic precursor were studied,and the morphology of fiber monolithic ceramic precursor was effectively controlled by adjusting the PVB,PEG content,and solid content.When the content of PVB and PEG in the precursor cell slurry of fiber monolith ceramic was 20wt.%and 12 wt.%,respectively,and the content of PVB,PEG,and DBP in the interface layer slurry of fiber monolithic ceramic precursor cell was 20 wt.%,10 wt.%,and 4wt.%,respectively,a fiber monolith precursor with a smooth surface and a certain strength was prepared.By controlling the solid content of the slurry,the uniformity of the diameter of the precursor cell was improved.The microstructure and mechanical properties of FZS_w and FZB ceramics were studied.The cell length of FZS_w and FZB was about 480μm and 600μm respectively,and the thickness of interface layer was 20μm.The bending strength of FZS_w and FZB were 117.4 MPa and 100.3 MPa,respectively.The fracture toughness of FZS_w and FZB were 2.97 MPa m^1/2 and 1.64 MPa m^1/2,respectively.The lower bending strength and fracture toughness were attributed to the lower density,and the fracture work of FZS_wand FZB were 94.1 J/m² and 98.4 J/m²,respectively.This was due to the introduction of the interface layer of ZrB₂-based fiber monolith,which made the cracks deflect or debond at the interface.FZS_w and FZB were tested for 200 s long-term plasma ablation at a high heat flux of 12.84 MW/m².FZS_w remains intact,while FZB was delaminated.The linear ablation rate and mass ablation rate of FZS_w were-0.2μm/s and-0.34 mg/s,respectively,and FZS_w showed better ablation resistance.After finite element analysis,the maximum thermal stress of FZS_w ablation center at the highest temperature reached 112.5 MPa,which was slightly lower than the bending strength of 117.4 MPa,so the sample remained intact after testing.The maximum thermal stress of FZB was 108.7 MPa,which was slightly higher than its bending strength（100.3 MPa）,which led to delamination of FZB after testing.