Preparation And Properties Of Transition Metal Boride-based Ultra-high Temperature Ceramic Materials

When a hypersonic vehicle（flights speed exceeding Mach 5）is flying at high speed in the atmosphere for a long time,the severe aerodynamic heating environment poses huge challenges to the structure and thermal protection of the aircraft,especially for thermal protection materials.Transition group refractory metal borides,carbides and their composites can maintain good physical and chemical properties at high temperatures,and are ultra-high temperature ceramic materials with good performance,which have recently attracted attentions.Refractory metal borides and carbides have excellent properties such as high melting point,high hardness,ablation resistance,high temperature oxidation resistance,high thermal conductivity and electrical conductivity,and have broad application prospects in the aerospace field.The most widely studied compounds are Zr B₂,Zr C,Hf B₂,Hf C and their composite materials.The sintered compactness of single-phase metal borides and carbides is poor,which affects their application.In this paper,Zr B₂-based and Hf B₂-based ultra-high temperature ceramics were synthesized by high pressure method,and the crystal structure,microstructure and microhardness of the materials were tested and analyzed.The ultra-high temperature ablation performance of the material was tested by using acetylene-oxygen flame.The results show that the high-pressure preparation method of Zr B₂-based and Hf B₂-based ultra-high temperature ceramics has the advantages of low synthesis temperature,simple process and short synthesis time.More importantly,the prepared Zr B₂-Zr C and Hf B₂-Hf C have excellent ultra-high temperature sintering resistance and corrosion properties.Among them,after the Zr B₂-Zr C composite ceramic material was ablated at2000℃for 60 s,the best linear ablation rate was 6μm/s,and the best mass ablation rate was 30μg/s;after the Hf B₂-Hf C composite ceramic material was ablated at 1600℃for 60 s,the optimal mass ablation rate was 3.83μg/s,and the optimal linear ablation rate was 2μm/s.In this paper,the synthesis of high-hardness refractory metal boride WB₄ and its ablation resistance were studied.The WB₄ prepared by the DC arc melting method showed good ablation resistance at 900℃,the mass ablation rate was 1.08μg/s,and the linear ablation rate was 0.167μm/s.The hardness and ablation properties of the WB₄-diamond composites prepared by the high-pressure did not appear to be significantly improved.