Medium-Entropy (Zr_1/3Hf_1/3W_1/3)C Ceramics Toughened by In-Situ-Formed Silicon Carbide via Low-Temperature Reactive Spark Plasma Sintering

Abstract

Medium-entropy transition metal carbide ceramics and their composites are important materials for extreme environments. However, they face challenges in densification difficulties and low fracture toughness. To address this issue, a medium-entropy ceramic powder with a nominal composition of (Zr_1/3Hf_1/3W_1/3)C (MEC) was synthesized by carbothermal reduction. Then, silicon (Si) was added, and the reactive spark plasma sintering (RSPS) technology was used to prepare MEC-based composite ceramics. The results show that MEC ceramics without Si addition can only form a single-phase solid solution when sintered at 1 900 ℃, with a relative density of 96.7% and an average grain size of (3.8 ± 1.3) μm. By adding 5% Si by mass, the MEC-based composite ceramic with a relative density of 98.8% can be obtained by sintering at a relatively low temperature of 1 700 ℃. It is composed of an MEC solid solution phase and an in-situ-formed silicon carbide (SiC) secondary phase, and the average grain size of the MEC matrix phase is only (1.4 ± 0.3) μm. Compared with the single-phase MEC ceramic, the fracture toughness of the MEC-based composite ceramic prepared by adding Si increases by 24.8% to (3.42 ± 0.24) MPa·m ^1/2. It is considered that Si, with a low melting point, can form a liquid phase during sintering, promoting densification. Additionally, the reaction between Si and carbide results in the formation of carbon vacancies in the latter, which can accelerate atomic diffusion and promote the formation of the MEC solid solution phase. In addition, the in-situ-formed SiC not only pins the grain boundaries of the matrix phase to hinder its growth, but also causes crack deflection to improve the fracture toughness of materials. The research results can provide references for the design and preparation of novel medium-entropy carbide-based ceramics for extreme environments.

Keywords

medium-entropy carbide / carbothermal reduction / reactive sintering / silicon carbide / toughening

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Funding

National Natural Science Foundation of China(52371023)

National Natural Science Foundation of China(52032001)