Ablation-resistant high-entropy carbide-high-entropy boride-silicon carbide composite ceramic and preparation method thereof

Abstract

The invention relates to ablation-resistant high-entropy carbide-high-entropy boride-silicon carbide composite ceramic and a preparation method thereof.The method comprises the following steps that 1, transition metal oxide mixed powder, nanometer carbon black and SiB6 powder are mixed to form precursor powder; and (2) carrying out pressureless reaction sintering on the precursor powder to obtain the ablation-resistant high-entropy carbide-high-entropy boride-silicon carbide composite ceramic with the density of 96% or above. Compared with the prior art, the high-entropy ultrahigh-temperature composite ceramic with excellent high-temperature oxidation resistance and ablation resistance is prepared by taking SiB6 as a Si source and a B source through a carbon-boron-silicification reaction and a solid solution synergistic interaction pressureless reaction sintering method, and a compact and stable oxidation protection layer is formed after Si and B synergistically induce the ceramic to be ablated. The preparation method is simple, the cost is low, the element composition and structure and the block size are controllable, and the preparation method has a wide development prospect.

Description

technical field [0001] The invention relates to the field of thermal protection materials, in particular to an ablation-resistant high-entropy carbide-high-entropy boride-silicon carbide composite ceramic and a preparation method thereof. Background technique [0002] The thermal protection systems and key thermal structural components of hypersonic vehicles are in urgent need of ultra-high temperature structural materials that are resistant to high temperature (>2000°C), oxidation resistance and ablation resistance (anti-oxidation and resistance to mechanical erosion, shear, etc.) in extreme environments. High-entropy carbide ceramics is a single-phase compound with NaCl structure formed by equimolar or nearly equimolar ratio of 5 or more transition metal elements and carbon elements. The "entropy stable" single-phase structure enables it to have: ① high entropy effect on thermodynamics; ② lattice distortion effect on structure; ③ hysteresis diffusion effect on kinetics;...

AI Technical Summary

Problems solved by technology

However, the preparation of high-entropy ultra-high-temperature ceramics by SPS has the following two defects: on the one hand, the activation energy of the reaction between carbides and borides is low, and the densification of reaction sintering is difficult, and it needs to be reacted at a high temperature of 2200 ° C to complete the solid solution. This causes the grains to grow abnormally, and there are pores at the grain boundaries; on the other hand, SPS is limited to the preparation of small-sized samples, and cannot prepare complex shapes and large-sized samples.

[0010] To prepare high-entropy carbide ceramics, on the one hand, traditional pressureless sintering methods use transition metal oxides or carbides as raw materials, and the reaction system has low sintering activity, resulting in sintering The activation energy is high, and the sintering temperature is as high as 2200-2500°C, which causes abnormal grain growth; on the other hand, the increase of the sintering temperature leads to an increase in the migration rate of the grain boundary, resulting in the generation of closed pores in the crystal in the ceramic, which becomes the late crack initiation. source of

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