Abstract: The development of low-cost hard materials with strong corrosion resistance and good electrical conductivity is important for many industrial applications, such as aluminum electrolysis. High electrical conductivity is one hallmark of metals arising from the itinerant nature of metallic bonds, but such metals easily dissolve in high-temperature electrolytes and are soft. In contrast, covalent solids possess strong corrosion resistance and high hardness. However, such localized covalent bonds are unfavorable for electron transport, leading to poor electrical conductivity. In this work, we report the synthesis of two less expensive high-entropy dodecaboride ceramic composites using boron thermal reduction and spark plasma sintering methods. Immersion corrosion tests indicate that the ultimate corrosion rates are half that of common corrosion-resistant steels and much lower than those of high-entropy alloys and oxides, suggesting that two newly developed ceramic composites are highly corrosion-resistant materials. Comprehensive cross-section microstructural characterizations show that the corrosion process is primarily controlled by a diffusion mechanism. The resistivity and hardness measurements display that both possess metallic conductivity and high hardness. Combined with theoretical calculations, we reveal that the good corrosion resistance is closely associated with the strong chemical inertness of the matrix and the formation of the barrier layer at the corrosion interfaces. The stiff three-dimensional boron network forms robust conducting channels for transporting valence electrons that are responsible for metallic conductivity; the superposition of a highly stable covalent network and high-entropy solid solution achieves strong chemical inertness and high hardness. This class of less expensive high-entropy ceramic composites with multiple properties can be potential inert anode materials in the aluminium electrolysis industry.

Key words: High-entropy dodecaboride ceramic composites, Corrosion resistance, Electrical conductivity, Hardness, Inert anode