Abstract
Multi-component solid solutions with non-stoichiometric compositions are characteristics of ultra-high temperature carbides as promising materials for hypersonic vehicles. However, for group IV transition-metal carbides, the oxidation behavior of multi-component non-stoichiometric (Zr,Hf,Ti)Cx carbide solid solution has not been clarified yet. The present work fabricated four kinds of (Zr,Hf,Ti)Cx carbide solid solution powders by free-pressureless spark plasma sintering to investigate the oxidation behavior of (Zr,Hf,Ti)Cx in air. The effects of metallic atom composition on oxidation resistance were examined. The results indicate that the oxidation kinetics of (Zr,Hf,Ti)Cx are composition dependent. A high Hf content in (Zr,Hf,Ti)Cx was beneficial to form an amorphous Zr-Hf-Ti-C-O oxycarbide layer as an oxygen barrier to enhance the initial oxidation resistance. Meanwhile, an equiatomic ratio of metallic atoms reduced the growth rate of (Zr,Hf,Ti)O2 oxide, increasing its phase stability at high temperatures, which improved the oxidation activation energy of (Zr, Hf, Ti)Cx.
Highlights
IntroductionNovel single-phase multi-component (e.g., (Hf,Ta)C [11,12,13,14,15], (Zr,Nb,Ti)C [16], and Zr0.8Ti0.2C0.74B0.26 [17]) or high-entropy [18,19] carbides have attracted considerable attention for their extremely high melting points (~3930 °C) [20,21], high hardness [22,23], low thermal conductivity [24,25], and better oxidation resistance [15,26]
The results show that the highentropy carbide obtains a good oxidation resistance, which is ascribed to their high mixing entropy, creating a high-entropy effect on lattice deformation and the formation of a dense oxide to reduce the inward diffusion of O2 [28] or H2O [27]
The obtained Zr0.3Hf0.5Ti0.2C0.8 carbide has been characterized in Ref. [48], but we present the basic information for the sake of clarity, and compare it to other three kinds of (Zr,Hf,Ti)Cx carbides in different compositions
Summary
Novel single-phase multi-component (e.g., (Hf,Ta)C [11,12,13,14,15], (Zr,Nb,Ti)C [16], and Zr0.8Ti0.2C0.74B0.26 [17]) or high-entropy [18,19] carbides have attracted considerable attention for their extremely high melting points (~3930 °C) [20,21], high hardness [22,23], low thermal conductivity [24,25], and better oxidation resistance [15,26]. For (Zr,Hf,Ti)C carbide solid solution, as a medium entropy ceramic [30], a clear understanding of its oxidation behavior has not been achieved. The effects of variation in composition of metallic atoms on oxidation behavior and oxidation resistance of (Zr,Hf,Ti)C are needed to be clarified
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