Effects of (Ta0.2W0.2Nb0.2Mo0.2V0.2)C high-entropy carbide content on the microstructure and properties of Ti(C0.7N0.3)-based cermet

Using pre-synthesized high-entropy (Ta_0.2W_0.2Nb_0.2Mo_0.2V_0.2)C carbide as the reinforcing phase, Ti(C_0.7N_0.3)-based cermets were prepared by pressureless sintering at 1600 °C. The results revealed that due to the solid solution reaction between the mono-carbide and (Ta_0.2W_0.2Nb_0.2Mo_0.2V_0.2)C, only one set of face-centered-cubic diffraction peaks in XRD was detected in the as-sintered cermets, alongside the typical core-rim structure. Compared to the Ti(C_0.7N_0.3)-based cermets without high-entropy reinforcing phase, the Vickers hardness was increased from 17.06 ± 0.09 GPa to 18.42 ± 0.33 GPa and the fracture toughness was increased from 9.21 ± 0.31 MPa m^1/2 to 12.56 ± 0.23 MPa m^1/2 by adding 10 wt% (Ta_0.2W_0.2Nb_0.2Mo_0.2V_0.2)C. The wear resistance of the cermet was enhanced significantly with increasing (Ta_0.2W_0.2Nb_0.2Mo_0.2V_0.2)C content. This work provided a potential that the high-entropy carbide can be applied as an effective reinforcing phase in the preparation of high-performance Ti(C_0.7N_0.3)-based cermets.     

A novel high-entropy monoboride (Mo0.2Ta0.2Ni0.2Cr0.2W0.2)B with superhardness and low thermal conductivity

A new high-entropy monoboride (Mo_0.2Ta_0.2Ni_0.2Cr_0.2W_0.2)B ceramic with a WB-type orthogonal structure was designed and synthesised by in-situ reactive hot pressing at 2000 °C and 30 MPa for 1.5 h under an argon atmosphere. The microstructure of the sintered samples was comprehensively characterised, and the formation of a high-entropy monoboride (Mo_0.2Ta_0.2Ni_0.2Cr_0.2W_0.2)B ceramic was confirmed. Owing to the high density of the dislocations and strengthening metal-boron bonds, the high-entropy (Mo_0.2Ta_0.2Ni_0.2Cr_0.2W_0.2)B ceramic exhibited a hardness of 48.51 ± 4.07 GPa, which enabled it to be classed as a new superhard material. In addition, the thermal conductivity (2.05 ± 0.10 W/(m·K) at 400 °C) and electric conductivity (132.30 S/cm) were determined.     

Oxidation behavior of high-entropy carbide (Hf0.2Ta0.2Zr0.2Ti0.2Nb0.2)C at 1400–1600 °C

Oxidation behavior of high-entropy carbide (Hf_0.2Ta_0.2Zr_0.2Ti_0.2Nb_0.2)C (HTZTNC) was investigated over temperature range of 1400–1600 °C. Results showed improved oxidation resistance of high-entropy carbide compared with individual carbide ceramics. In oxide layer, Ta₂O₅ and Nb₂O₅ were found to be dominant phases at 1400 °C, whereas ZrTiO₄ and HfTiO₄ were main phases obtained at 1500 and 1600 °C. Moreover, these complex dense oxide layer structures on the surface of HTZTNC at high temperature led to excellent oxidation resistance. The observation of Ti-depleted layer at 1500 and 1600 °C after 20 min of oxidation indicated that oxidation mechanism involved outward diffusion of titanium oxide, which was further confirmed by reoxidation experiments. In sum, these findings are promising for future development of high-entropy ultrahigh temperature ceramics with good oxidation resistance.     

Hardness and toughness improvement of SiC-based ceramics with the addition of (Hf0.2Mo0.2Ta0.2Nb0.2Ti0.2)B2

The influences of different contents ranging 0–15 wt% of high-entropy boride (HEB) (Hf_0.2Mo_0.2Ta_0.2Nb_0.2Ti_0.2)B₂ on the mechanical properties of SiC-based ceramics using Al₂O₃-Y₂O₃ sintering additives sintered by spark plasma sintering process were investigated in this study. The results showed that the introduction of 5 and 10 wt% (Hf_0.2Mo_0.2Ta_0.2Nb_0.2Ti_0.2)B₂ could facilitate the densification and the grain growth of SiC-based ceramics via the mechanism of liquid phase sintering. However, the grain growth of SiC-based ceramics was inhibited by the grain boundary pinning effect with the addition of 15 wt% (Hf_0.2Mo_0.2Ta_0.2Nb_0.2Ti_0.2)B₂. The SiC-based ceramics with 15 wt% (Hf_0.2Mo_0.2Ta_0.2Nb_0.2Ti_0.2)B₂ showed the enhanced hardness (21.9±0.7 GPa) and high toughness (4.88±0.88 MPa·m^1/2) as compared with high-entropy phase-free SiC-based ceramics, which exhibited a hardness of 16.6 GPa and toughness of 3.10 MPa·m^1/2. The enhancement in mechanical properties was attributed to the addition of higher hardness of HEB phase, crack deflection toughening mechanism, and presence of residual stress due to the mismatch of coefficient of thermal expansion.     

Enhancing cutting performance of Ti(C,N)-based cermet tools on nodular cast iron by incorporating high-entropy carbide

In this study, we investigated the cutting performance and wear mechanisms of Ti(C,N)-based cutting tools containing varying weight percentages (0%, 5%, 10%, and 15%) of high-entropy carbide (HEC) (V_0.2Nb_0.2 Mo_0.2Ta_0.2W_0.2)C phase, when used for turning nodular cast iron. According to the turning test results, the cermet cutting tools containing 0 wt%, 5 wt%, 10 wt%, and 15 wt% HEC phases demonstrated effective cutting lives of 402, 720, 632, and 465 s, respectively. The tool with 5 wt% HEC phase showed the best cutting performance. When cutting nodular cast iron with cermet cutting tools, the main wear mechanisms observed were diffusion, oxidation, adhesion, and abrasion on the flank surface, along with diffusion, oxidation, and abrasion on the rake surface. The results of this study indicated that (V_0.2Nb_0.2Mo_0.2Ta_0.2W_0.2)C could be adopted as an effective reinforced phase in the cermet cutting tools.     

Microstructure and dielectric properties of high entropy Ba(Zr0.2Ti0.2Sn0.2Hf0.2Me0.2)O3 perovskite oxides

A series of high entropy Ba(Zr_0.2Ti_0.2Sn_0.2Hf_0.2Me_0.2)O₃ (Me=Y³⁺,Nb⁵⁺,Ta⁵⁺,V⁵⁺,Mo⁶⁺,W⁶⁺) perovskite oxides were synthesized by using a solid state reaction method. Three multiple-cation solid solutions formed pure phase compounds, and only two compounds were sintered into ceramics. Microstructure analysis showed the influence of configurational entropy on phase stability and grain growth. Dielectric measurements showed that the high entropy ceramics possessed decent temperature stability of permittivity from 25 °C to 200 °C, low dielectric loss (<0.002) from 20 Hz to 2 MHz, high resistance and moderate breakdown strength (290 kV/cm, 370 kV/cm). Evidence strongly confirmed that controlling configurational entropy could be a feasible perspective to set up highly tunable perovskite structures and explore novel species of dielectric materials.     

High-entropy carbide-based ceramic cutting tools

In this study, a novel high-entropy carbide-based ceramic cutting tool was developed. The cutting performance of three kinds of high-entropy carbide-based ceramic tools with different mechanical properties for the ISO C45E4 steel were evaluated. Although the pure (Ti_0.2Zr_0.2Nb_0.2Ta_0.2Mo_0.2)C_0.8 ceramic cutting tool exhibited the highest hardness of 25.06 ± 0.32 GPa, the cutting performance was poor due to the chipping and catastrophic failure caused by the low toughness (2.25 ± 0.27 MPa m^1/2). The (Ti_0.2Zr_0.2Nb_0.2Ta_0.2Mo_0.2)C_0.8–15 vol% cobalt cutting tool with highest fracture toughness (6.37 ± 0.24 MPa m^1/2) and lowest hardness (17.29 ± 0.79 GPa) showed the medium cutting performance due to the low wear resistance caused by the low hardness. The (Ti_0.2Zr_0.2Nb_0.2Ta_0.2Mo_0.2)C_0.8–7.7 vol% cobalt cutting tool showed the longest effective cutting life of ∼67 min due to the high wear resistance and chipping resistance caused by the high hardness (21.05 ± 0.72 GPa), high toughness (5.35 ± 0.51 MPa m^1/2), and fine grain size (0.60 ± 0.15 μm). The wear mechanisms of the cobalt-containing (Ti_0.2Zr_0.2Nb_0.2Ta_0.2Mo_0.2)C_0.8 ceramic cutting tools included adhesive wear and abrasive wear and oxidative wear. This research indicated that the high-entropy carbide-based ceramics with high hardness and high toughness have potential use in the field of cutting tool application.     

Microstructures and oxidation mechanisms of (Zr0.2Hf0.2Ta0.2Nb0.2Ti0.2)B2 high-entropy ceramic

A nano dual-phase powder with great sinterability was synthesized by molten-salt assisted borothermal reductions at 1100 °C using B, ZrO₂, HfO₂, Ta₂O₅, Nb₂O₅ and TiO₂ powders as raw materials. Single-phase (Z_r0.2Hf_0.2Ta_0.2Nb_0.2Ti_0.2)B₂ high-entropy ceramic was prepared by spark plasma sintering using the as-synthesized nano dual-phase powder. Oxidation behavior of the (Zr_0.2Hf_0.2Ta_0.2Nb_0.2Ti_0.2)B₂ ceramic was investigated over the range of 30–1400 °C in air and the result indicated that the rapid oxidation of ceramic began at 1300 °C. The phenomenon could be ascribed to the rapid volatilization of B₂O₃ from oxide scale. A layered structure was formed at the cross section of (Zr_0.2Hf_0.2Ta_0.2Nb_0.2Ti_0.2)B₂ ceramic after oxidation. The relationship between partial pressures of gaseous metal oxides and oxygen partial pressures was calculated, which inferred that the formation of layered structure could be ascribed to the active oxidation of (Zr_0.2Hf_0.2Ta_0.2Nb_0.2Ti_0.2)B₂, the generation of gaseous metal oxides, their outward diffusion and further oxidation.     

Low-temperature synthesis of high-entropy (Hf0.2Ti0.2Mo0.2Ta0.2Nb0.2)B2 powders combined with theoretical forecast of its elastic and thermal properties

A theoretical calculation combined with experiment was used to study high-entropy (Hf_0.2Ti_0.2Mo_0.2Ta_0.2Nb_0.2)B₂ (HEB-HfTiMoTaNb). The theoretical calculation suggested HEB-HfTiMoTaNb could be stable over a wide temperature range. Then, a novel solvothermal/molten salt-assisted borothermal reduction method was proposed to efficiently pre-disperse transitional metal atoms in a precursor and synthesize (Hf_0.2Ti_0.2Mo_0.2Ta_0.2Nb_0.2)B₂ nanoscale powders at 1573 K for 6 h, which is nearly 300 K lower than previous reports. The characterization results indicated that the as-synthesized nanoscale HEB-HfTiMoTaNb powder was hexagonal single-phase with homogeneous elements distribution and uniform size, and the oxygen content of the particles is 0.97 wt%. Simultaneously, the mechanical properties, anisotropic nature, and thermal properties of HEB-HfTiMoTaNb were investigated by density functional theory (DFT) calculations. The Cannikin's law was adopted to explain the improvement of comprehensive mechanical properties. In addition, a significant reduction of thermal conductivity was observed for HEB-HfTiMoTaNb and it only was 1/15 of the value of HfB₂. This work suggests a reliable technique for synthesis of nanosized HEB powders and discovery of high-entropy materials under the guidance of first-principle theory.     

First-principles prediction,fabrication and characterization of (Hf0.2Nb0.2Ta0.2Ti0.2Zr0.2)B2 high-entropy borides

The microstructure and mechanical properties of (Hf_0.2Nb_0.2Ta_0.2Ti_0.2Zr_0.2)B₂ high-entropy boride (HEB) were first predicted by first-principles calculations combined with virtual crystal approximation (VCA). The results verified the suitability of VCA scheme in HEB studying. Besides, single-phase (Hf_0.2Nb_0.2Ta_0.2Ti_0.2Zr_0.2)B₂ ceramics were successfully fabricated using boro/carbothermal reduction (BCTR) method and subsequent spark plasma sintering (SPS); furthermore, the effects of different amounts of B₄C on microstructure and mechanical properties were evaluated. Due to the addition of B₄C and C, all samples formed single-phase solid solutions after SPS. When the excess amount of B₄C increased to 5 wt%, the sample with fine grains exhibited superior comprehensive properties with the hardness of 18.1 ± 1.0 GPa, flexural strength of 376 ± 25 MPa, and fracture toughness of 4.70 ± 0.27 MPa m^1/2. Nonetheless, 10 wt% excess of B₄C coarsened the grains and decreased the strength of the ceramic. Moreover, the nanohardness (34.5–36.9 GPa) and Young's modulus (519–571 GPa) values with different B₄C contents just showed a slight difference and were within ranges commonly observed in high-entropy diboride ceramics.     

Pressureless sintering and properties of (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)C high-entropy ceramics: The effect of pyrolytic carbon

A novel (Hf_0.2Zr_0.2Ta_0.2Nb_0.2Ti_0.2)C high-entropy ceramic was successfully prepared by pressureless sintering at 2200 °C. With increasing content of resin-derived-carbon, the density, and mechanical and thermal properties increased up to a maximum content of 2～4 wt% resin addition, after which further addition was detrimental. All specimens showed high strength (≥347±36 MPa), with the highest value achieving 450±64 MPa, and fracture toughness significantly higher (>20 %) than those of the corresponding monocarbides and Ta_0.5Hf_0.5C, (Ta_1/3Zr_1/3Nb_1/3)C. The thermal conductivity was approximately equivalent to the lowest value of the corresponding mono-carbides, which was assumed to be due to the lattice distortion effect.     

Synthesis and thermal stability of novel high-entropy metal boron carbonitride ceramic powders

High-entropy metal boron carbonitride ceramic powders including (Ta_0.2Nb_0.2Zr_0.2Hf_0.2W_0.2)BCN, (Ta_0.2Nb_0.2Zr_0.2Hf_0.2Ti_0.2)BCN, and (Ta_0.2Nb_0.2Zr_0.2Ti_0.2W_0.2)BCN, were successfully synthesized via mechanical alloying at room temperature. Results show that for the first step of 10 h milling, the amorphous BCN phases are observed. After 24 h of second step milling, the as-synthesized high-entropy ceramics exhibit a single face-centered cubic solid solution structure with high compositional uniformity from nano-scale to micron-scale. When heated to 1500 °C for 30min in flowing Ar, the as-prepared high-entropy ceramic powders still show relatively high thermal stability; however, some metals oxides like HfO₂ and ZrO₂ are detected due to the pre-existing oxides on sample surfaces. After heat treatment, some amorphous phases are still retained. This work suggests a new processing route on the synthesis of high-entropy metal boron carbonitride ceramics.     

Novel single phase (Ti0.2W0.2Ta0.2Mo0.2V0.2)C0.8 high entropy carbide using ball milling followed by reactive spark plasma sintering

Single phase novel (Ti_0.2W_0.2Ta_0.2Mo_0.2V_0.2)C_0.8 high entropy carbide (HEC) compacts were successfully synthesized by reactive spark plasma sintering of ball milled metal-carbon elemental mixture at temperatures of 1400−1800 °C. X-ray diffraction and element distribution maps indicated single phase carbide formation with lattice parameter ranging from 4.307 Å to 4.312 Å with small amount of TiO₂. X-ray energy dispersive spectroscopy (EDS) mapping showed uniform distribution of the transition metals in the carbide phase. The microhardness, elastic modulus, fracture toughness, electrical resistivity and thermal expansion coefficient (25 °C–600 °C) of the compact sintered at 1800 °C were found to be 25.8 ± 2.8 GPa, 461 ± 36 GPa, 3.7 ± 0.4 MPa.m^1/2, 7 × 10⁻⁴ Ω/m² and 7 × 10^-6 K⁻¹ respectively.     

Low-temperature synthesis of six-principal-component high-entropy transition-metal carbide aerogel thermal insulator

High-entropy transition-metal (IVB–VIB) carbide (HETMC) ceramics consisting of multiple principal components generally correspond to higher configuration entropy, and exhibit better overall performance. However, they also present certain synthesis challenges, for example, in the synthesis of a three-dimensional six-principal-component HETMC aerogel. In the present work, as an example a novel (Ti_0.167Cr_0.167V_0.167Mo_0.167Nb_0.167Ta_0.167)C aerogel was prepared at a relatively low temperature of 1773 K by an in-situ carbothermal reduction/partial sintering technique following the successful preparation of (Ti_0.2V_0.2Mo_0.2Nb_0.2Ta_0.2)C and (Ti_0.2Cr_0.2Mo_0.2Nb_0.2Ta_0.2)C five-principal-component HETMC aerogels. The synthesized 6-HETMC aerogel exhibited a homogeneous microstructure with grain phases and pores of 100–300 nm and 0.2–10 μm, respectively, a density of 0.45 g cm⁻³, a high porosity and compressive strength of 94.5% and 0.8 MPa, respectively, a low thermal conductivity of 0.128 W (m K)⁻¹ at 298 K, and a good high-temperature stability at least up to 1673 K in Ar. This research provided a novel strategy for future development of HETMC ceramic aerogels for high-temperature applications.     

Rare-earth-tantalate high-entropy ceramics with sluggish grain growth and low thermal conductivity

A series of rare-earth-tantalate high-entropy ceramics ((5RE_0.2)Ta₃O₉, where RE = five elements chosen from La, Ce, Nd, Sm, Eu and Gd) were prepared by conventional sintering in air at 1500 ^°C for 10 h. The (5RE_0.2)Ta₃O₉ high-entropy ceramics exhibit an orthogonal structure and sluggish grain growth. No phase transition occurs in the test temperature of 25–1200 ^°C. The thermal conductivities of all (5RE_0.2)Ta₃O₉ ceramics are in the range of 1.14–1.98 W m^?1 K^?1 at a test temperature of 25–500 ^°C, approximately half of that of YSZ. The sample of (Gd_0.2Ce_0.2Nd_0.2Sm_0.2Eu_0.2)Ta₃O₉ exhibits a low glass-like thermal conductivity with a value of 1.14 W m^?1 K^?1 at 25 ^°C. The thermal expansion coefficient of (5RE_0.2)Ta₃O₉ ceramics ranges from 5.6 × 10^?6 to 7.8 × 10^?6 K^?1 at 25–800 ^°C, and their fracture toughness is high (3.09–6.78 MPa·m^1/2). The results above show that (5RE_0.2)Ta₃O₉ ceramics could be a promising candidate for thermal barrier coatings.     

High-entropy rare-earth disilicate (Lu0.2Yb0.2Er0.2Tm0.2Sc0.2)2Si2O7: A potential environmental barrier coating material

A new high-entropy ceramic (Lu_0.2Yb_0.2Er_0.2Tm_0.2Sc_0.2)₂Si₂O₇ ((5RE_0.2)₂Si₂O₇) was proposed as a potential environmental barrier coating (EBC) material for ceramics matrix composites in this work. Experimental results showed that the (5RE_0.2)₂Si₂O₇ synthesized by solid-phase sintering was a monoclinic solid solution and had good phase stability proved by no obvious absorption/exothermic peak in the DSC curve from room temperature to 1400 °C. It performed a lower coefficient of thermal expansion (2.08 ×10^?6-4.03 ×10^?6 °C^?1) and thermal conductivity (1.76–2.99 W?m^?1?°C^?1) compared with the five single principal RE₂Si₂O₇. In water vapor corrosion tests, (5RE_0.2)₂Si₂O₇ also exhibited better water vapor corrosion resistance attributed to the multiple doping effects. The weight loss was only 3.1831 × 10^?5 g?cm^?2 after 200 h corrosion at 1500 °C, which was lower than that of each single principal RE₂Si₂O₇. Therefore, (5RE_0.2)₂Si₂O₇ could be regarded as a remarkable candidate for EBCs.     

High-entropy (HfTaTiNbZr)C and (HfTaTiNbMo)C carbides fabricated through reactive high-energy ball milling and spark plasma sintering

Powders of high-entropy Hf_0.2Ta_0.2Ti_0.2Nb_0.2Zr_0.2C (HEC_Zr) and Hf_0.2Ta_0.2Ti_0.2Nb_0.2Mo_0.2C (HEC_Mo) carbides were fabricated through the reactive high-energy ball milling (R-HEBM) of metal and graphite particles. It was found that 60 min of R-HEBM is adequate to achieve a full conversion of the initial precursors into a FCC solid solution for both compositions. The HEC_Zr powder possesses a unimodal particle size distribution (40% d ≤ 1 μm, 95% d ≤ 10 μm), and the HEC_Mo powder features a bimodal distribution with a slightly larger particle size overall (30% d ≤ 1 μm, 80% d ≤ 10 μm). Bulk high-entropy ceramics with a minor presence of an oxide phase were fabricated through the spark plasma sintering of these high-entropy powders at 2000 °C with a 10 min dwelling time. The HEC_Zr ceramics possess a relative density of up to 94.8%, hardness of 25.7 ± 3.5 GPa, Young's modulus of 473 ± 37 GPa, and thermal conductivity of 5.6 ± 0.1 W/m·K. HEC_Mo ceramics with a relative density of up to 93.8%, hardness of 23.8 ± 2.7 GPa, Young's modulus of 544 ± 48 GPa, and thermal conductivity of 5.9 ± 0.2 W/m·K were also fabricated. A comparison of the properties of the HECs produced in this study and those previously reported is also provided.     

Effect of carbon content on the microstructure and mechanical properties of high-entropy (Ti0.2Zr0.2Nb0.2Ta0.2Mo0.2)Cx ceramics

High-entropy (Ti_0.2Zr_0.2Nb_0.2Ta_0.2Mo_0.2)C_x ceramics, with different carbon contents (x=0.55?1), were prepared by spark plasma sintering using powders synthesized via a carbothermal reduction approach. Single-phase, high-entropy (Ti_0.2Zr_0.2Nb_0.2Ta_0.2Mo_0.2)C_x ceramics could be obtained when using a carbon content of x=0.70?0.85. Combined ZrO₂ and Mo-rich carbide phases, or residual graphite, existed in the ceramics due to either a carbon deficiency or excess at x=0.55 and 1, respectively. With the carbon content increased from x=0.70 to x=0.85, the grain size decreased from 4.36 ± 1.55 μm to 2.00 ± 0.91 μm, while the hardness and toughness increased from 23.72 ± 0.26 GPa and 1.69 ± 0.21 MPa·m^1/2 to 25.45 ± 0.59 GPa and 2.37 ± 0.17 MPa·m^1/2, respectively. This study showed that the microstructure and mechanical properties of high-entropy carbide ceramics could be adjusted by the carbon content. High carbon content is conducive to improving hardness and toughness, as well as reducing grain size.     

(Ti0.2V0.2Cr0.2Nb0.2Ta0.2)2AlC–(Ti0.2V0.2Cr0.2Nb0.2Ta0.2)C high-entropy ceramics with low thermal conductivity

In recent years, the microstructure and physicochemical properties of high-entropy ceramics have received much interest by the combination of multiple principal elements. Herein, (Ti_0.2V_0.2Cr_0.2Nb_0.2Ta_0.2)₂AlC–(Ti_0.2V_0.2Cr_0.2Nb_0.2Ta_0.2)C high-entropy ceramics (M₂AlC-MC HECs) were prepared by the spark plasma sintering (SPS) technique, attributing to the structural and chemical diversity of MAX phases. The microstructure of M₂AlC-MC HECs was characterized from micron to atomic scales, and the phase composition of M₂AlC-MC HECs was analyzed by a combination of Maud and Rietveld analysis. The results indicate the successful solid solution of Ti, V, Cr, Nb, and Ta atoms in the M-site of the 211-MAX configuration, and all the samples show a classic layered structure. The weight percentage of (Ti_0.2V_0.2Cr_0.2Nb_0.2Ta_0.2)₂AlC in the M₂AlC-MC HECs was more than 90%. Furthermore, the thermoelectric properties of M₂AlC-MC HECs were investigated for the first time in this study, and the electrical conductivity and thermal conductivity of HECs are 3278 S cm⁻¹ and 2.78 W m⁻¹ K⁻¹at 298 K, respectively.     

High-temperature oxidation behavior of (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)C high-entropy ceramics in air

High-entropy metal carbides have recently been arousing considerable interest. Nevertheless, their high-temperature oxidation behavior is rarely studied. Herein the high-temperature oxidation behavior of (Hf_0.2Zr_0.2Ta_0.2Nb_0.2Ti_0.2)C high-entropy metal carbide (HEC-1) was investigated at 1573-1773 K in air for 120 minutes. The results showed that HEC-1 had good oxidation resistance and its oxidation obeyed a parabolic law at 1573-1673 K, while HEC-1 was completely oxidized after isothermal oxidation at 1773 K for 60 minutes and thereby its oxidation followed a parabolic-linear law at 1773 K. An interesting triple-layered structure was observed within the formed oxide layer at 1673 K, which was attributed to the inward diffusion of O₂ and the outward diffusion of Ti element and CO or CO₂ gaseous products.