Mechanisms responsible for enhancing low‐temperature oxidation resistance of nonstoichiometric (Zr,Ti)C

Abstract

A series of (Zr,Ti)Cx (x = 0.7–1.0) samples were fabricated by a modified spark plasma sintering apparatus to investigate the effects of carbon concentration and Ti substitutions on the oxidation behavior. Crushed powders of (Zr,Ti)Cx were oxidized in lab air (N2–20‐vol.% O2) from room temperature to 900°C. The results indicated that Zr0.8Ti0.2C0.8, with a nominal carbon concentration x = 0.8, displayed good oxidation resistance, which was attributed to the formation of dense t‐(Zr,Ti)O2 oxide solid solution. During the oxidation of (Zr,Ti)Cx, Ti substitutions for Zr enhanced the outward diffusion of carbon, enabling a uniform carbon layer and a Zr–Ti–C–O layer on the surface of carbides. The formed carbon layer improved the oxidation resistance of (Zr,Ti)Cx below 550°C, where carbon is relatively oxidation resistant. Increasing the Ti concentration was found to enhance the oxidation resistance of (Zr,Ti)Cx with an increased oxidation onset temperature (672 ± 2°C for Zr0.8Ti0.2C0.8).

Nb- and Ta-doped (Hf,Zr,Ti)C multicomponent carbides with enhanced oxidation resistance at 2500 °C

“…13 Nb-and Ta-doped (Hf,Zr,Ti)C multicomponent carbides with enhanced oxidation resistance at 2500 °C structure until the oxygen content of the carbide lattice reaches its maximum solubility. As oxygen continues to diffuse inward and reaches the interface between the oxide layer and the matrix, the oxidation of carbon occurs after that of metallic elements [20,38,39]. Consequently, the Hf and Zr atoms within the M-C-O-1 phase preferentially react with oxygen to form (Hf,Zr)O 2 , thereby generating an M-C-O-2 phase with a higher Ti/Nb/Ta content (Fig.…”

Oxidation behavior of boron-containing (Zr,Ti)C x B y solid solution ceramics at 1600 °C in air

“…The as-synthesized (Zr,Ti)C x and (Zr,Ti)C x B y powders were utilized as raw materials for sintering (Zr,Ti)C x and (Zr,Ti)C x B y ceramics, both of which were single-phase solid solution with the FCC structure [21,25]. The preparation of the (Zr,Ti)C x solid solution powders used elemental powders as starting materials, including Zr (purity > 99.5 wt%, impurity Hf < 0.5 wt%, particle size ≤ 50 µm), Ti (purity > 99.5 wt%, impurity O < 0.2 wt%, H < 0.2 wt%, particle size ≤ 50 µm), and carbon (graphite, 99.95 wt%, 3 µm, Macklin Biochemical Co., Ltd., China).…”

“…The preparation of the (Zr,Ti)C x solid solution powders used elemental powders as starting materials, including Zr (purity > 99.5 wt%, impurity Hf < 0.5 wt%, particle size ≤ 50 µm), Ti (purity > 99.5 wt%, impurity O < 0.2 wt%, H < 0.2 wt%, particle size ≤ 50 µm), and carbon (graphite, 99.95 wt%, 3 µm, Macklin Biochemical Co., Ltd., China). They were fabricated by the modified SPS apparatus (HP D 25-3, FCT Systeme GmbH, Germany), and the details were reported in the prior work [21]. The (Zr,Ti)C x B y solid solution powders were synthesized using the (Zr,Ti)C x powders and B 2 O 3 (Aladdin, amorphous) as a boron source by solid-state diffusion of boron atoms, and the details were shown in the work [25].…”

“…The atomic ratio of Zr : Ti was designed to 3 : 1 due to their good oxidation resistance, which was also related to good ablation resistance of the C/C-(Zr 0.8 Ti 0.2 )C 0.74 B 0.26 composite [22], where (Zr 0.8 Ti 0.2 )C 0.74 B 0.26 owned a high atomic ratio of Zr/Ti. Further, (Zr,Ti)C x displayed good oxidation resistance when x is ~0.8 [21]. Therefore, the compositions of the samples were designed as nonstoichiometric (Zr 0.75 Ti 0.25 )C 0.82 and (Zr 0.75 Ti 0.25 )C 0.82 B 0.06 .…”

“…Wuchina et al [20] found that HfC 0.67 had a thinner oxide scale compared to HfC 0.98 after oxidation below 1600 ℃ in air, suggesting a slower oxidation rate. Meanwhile, among (Zr 0.8 Ti 0.2 )C x (x is the mole ratio of carbon to metal, x = 0.7-1.0) [21], (Zr 0.8 Ti 0.2 )C 0.8 with a nominal carbon concentration (x = 0.8) displays good oxidation resistance below 900 ℃ in air. This is attributed to the formation of dense t-(Zr,Ti)O 2 oxide solid solution with fewer cracks as an oxygen barrier during oxidation.…”