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1.
Xueliang Yan Loic Constantin Yongfeng Lu Jean‐François Silvain Michael Nastasi Bai Cui 《Journal of the American Ceramic Society》2018,101(10):4486-4491
A novel high‐entropy carbide ceramic, (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)C, with a single‐phase rock salt structure, was synthesized by spark plasma sintering. X‐ray diffraction confirmed the formation of a single‐phase rock salt structure at 26‐1140°C in Argon atmosphere, in which the 5 metal elements may share a cation position while the C element occupies the anion position. (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)C exhibits a much lower thermal diffusivity and conductivity than the binary carbides HfC, ZrC, TaC, and TiC, which may result from the significant phonon scattering at its distorted anion sublattice. (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)C inherits the high elastic modulus and hardness of the binary carbide ceramics. 相似文献
2.
Lei Yu Jian Yang Tai Qiu Jingxian Zhang Limei Pan 《Journal of the American Ceramic Society》2014,97(9):2950-2956
The microstructure, mechanical, and thermal properties of in situ hot‐pressed 30 vol% (ZrB2+ZrC)/Zr3[Al(Si)]4C6 composite have been investigated and compared with monolithic Zr3[Al(Si)]4C6 ceramic. The composite is composed of ZrB2 and ZrC grains embedded in a Zr3[Al(Si)]4C6 matrix. The composite shows superior hardness (Vickers hardness of 16.4 GPa), stiffness (Young's modulus of 415 GPa), strength (bending strength of 621 MPa), and toughness (fracture toughness of 7.37 MPa·m1/2) compared with monolithic Zr3[Al(Si)]4C6. The composite retains high modulus of 357 GPa at 1430°C (86% of that at ambient temperature) due to clean grain boundaries with no glassy phase. In addition, the composite exhibits higher specific heat capacity and thermal conductivity but slightly lower coefficient of thermal expansion compared with monolithic Zr3[Al(Si)]4C6. The calculation of the thermal stress fracture resistance parameter (R) predicts a much improved thermal shock resistance of the composite. Based on these results, (ZrB2+ZrC)/Zr3[Al(Si)]4C6 composites show promising potential for high‐temperature and ultra high‐temperature applications. 相似文献
3.
《Ceramics International》2022,48(3):3762-3770
Cf/Hf0.5Zr0.5C-SiC composites were prepared by introducing Hf0.5Zr0.5C matrix (11 cycles) and SiC matrix (9 cycles) into the carbon cloth preform through precursor impregnation and pyrolysis (PIP) process. The influence of the introduction time of SiC matrix on the microstructure and mechanical properties of Cf/Hf0.5Zr0.5C-SiC composites was studied, and the results show that with the increase of the PIP cycles of the SiC matrix introduced before Hf0.5Zr0.5C matrix, the composite open porosity decreased, and the flexural strength and modulus presented an obvious upward trend. CS45 sample, which has 4 cycles of PIP SiC introduced in advance, has the highest flexural strength, flexural modulus and interfacial shear strength of 402.73 ± 35.73 MPa, 56.92 ± 3.97 GPa and 100.88 ± 7.79 MPa, respectively. Hf0.5Zr0.5C matrix has a loose and porous structure, so when more SiC matrix was introduced in advance, its covering effect on the surface of fibers led to less intra-bundle pores and thusly denser composite structure, and due to the compactness of SiC matrix, better overall bonding of fiber, interface and matrix was achieved, as well as better load transfer effect, which led to obvious interfacial debonding and cracking based on the in-situ SEM observation during flexural tests. While in the sample without pre-introduced SiC, the cracking occurred mainly between the interface and porous matrix and the overall performance of the material was poor. 相似文献
4.
Tongqi Wen Beilin Ye Manh Cuong Nguyen Mengdong Ma Yanhui Chu 《Journal of the American Ceramic Society》2020,103(11):6475-6489
In this work, a novel (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)(N0.5C0.5) high-entropy nitride-carbide (HENC-1) with multi-cationic and -anionic sublattice structure was reported and their thermophysical and mechanical properties were studied for the first time. The results of the first-principles calculations showed that HENC-1 had the highest mixing entropy of 1.151R, which resulted in the lowest Gibbs free energy above 600 K among HENC-1, (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)N high-entropy nitrides (HEN-1), and (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)C high-entropy carbides (HEC-1). In this case, HENC-1 samples were successfully fabricated by hot-pressing sintering technique at the lowest temperature (1773 K) among HENC-1, HEN-1 and HEC-1 samples. The as-fabricated HENC-1 samples showed a single rock-salt structure of metal nitride-carbides and high compositional uniformity. Meanwhile, they exhibited high microhardness of 19.5 ± 0.3 GPa at an applied load of 9.8 N and nanohardness of 33.4 ± 0.5 GPa and simultaneously possessed a high bulk modulus of 258 GPa, Young's modulus of 429 GPa, shear modulus of 176 GPa, and elastic modulus of 572 ± 7 GPa. Their hardness and modulus are the highest among HENC-1, HEN-1 and HEC-1 samples, which could be attributed to the presence of mass disorder and lattice distortion from the multi-anionic sublattice structure and small grain in HENC-1 samples. In addition, the thermal conductivity of HENC-1 samples was significantly lower than the average value from the “rule of mixture” between HEC-1 and HEN-1 samples in the range of 300-800 K, which was due to the presence of lattice distortion from the multi-anionic sublattice structure in HENC-1 samples. 相似文献
5.
Beilin Ye Yanhui Chu Kehan Huang Da Liu 《Journal of the American Ceramic Society》2019,102(3):919-923
(Zr1/3Nb1/3Ti1/3)C metal carbide solid-solution ceramic has been successfully fabricated by hot pressing sintering at 2473 K using ZrC, NbC, and TiC powders as raw materials. The results show that the as-prepared solid-solution ceramic possesses a single rock-salt crystal structure of metal carbides and simultaneously exhibits high compositional uniformity from nanoscale to microscale. By taking advantage of these unique features, it shows relatively high hardness of 38.8 ± 4.4 Gpa and elastic modulus of 481.8 ± 31.0 Gpa and relatively low thermal conductivity of 17.1 ± 0.3 W/(m·K) and thermal diffusivity of 6.1 ± 0.1 mm2/s, which may attribute primarily to the presence of solid solution effects. 相似文献
6.
《Journal of the European Ceramic Society》2023,43(8):3043-3052
There is an urgent need for the thermal protection of carbon/carbon composites to increase their service span in aerospace field. As members of ultra-high temperature ceramics, HfC and ZrC are thought to be alternative materials, but their poor oxidation behavior and fracture toughness at temperature over 2000 ℃ prevent them from taking full advantages. Herein, we synthesized nanosized Hf6Ta2O17 powders and introduced them into HfC ceramic to tackle the above problems. Plasma-sprayed HfC coatings with Hf6Ta2O17 varied from 0 to 15 mol.% (0, 1.25, 2.5, 5, 15) were exposed to an oxyacetylene torch with a heat flux of 2.38 MW/m2. The one with 2.5 mol.% Hf6Ta2O17 showed the best ablation resistance. Smaller doping was unable to effectively hinder oxygen diffusion given the inadequate compactness of the formed scale, conversely substantial humps and ruptures formed on the samples with higher amounts, acting as straightforward paths for oxygen. 相似文献
7.
《Ceramics International》2020,46(11):19008-19014
Powders of high-entropy Hf0.2Ta0.2Ti0.2Nb0.2Zr0.2C (HECZr) and Hf0.2Ta0.2Ti0.2Nb0.2Mo0.2C (HECMo) 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 HECZr powder possesses a unimodal particle size distribution (40% d ≤ 1 μm, 95% d ≤ 10 μm), and the HECMo 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 HECZr 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. HECMo 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. 相似文献
8.
《Journal of the European Ceramic Society》2021,41(15):7450-7463
To improve the ablation performance of C/C composites, HfC/PyC core-shell structure nanowire (HfCnw/PyC)-reinforced Hf1-xZrxC coating was prepared via three-step chemical vapor deposition (CVD) method. Effects of HfCnw/PyC and PyC layer thickness on the microstructure, residual stress and ablation performance of Hf1-xZrxC coating were studied. HfCnw/PyC-reinforced coatings exhibited equiaxial crystal structure. After incorporating HfCnw/PyC, ablation property of Hf1-xZrxC coating was enhanced because of the skeleton role of HfO2 nanowires. PyC possessed low coefficient of thermal expansion (CTE) and high heat conductivity, but poor ablation performance. Hence, with the increase in thickness of PyC layer, ablation property of the coating first increased and then decreased. HfCnw/PyC-reinforced Hf1-xZrxC coating with PyC layer thickness of about 50 nm exhibited the best ablation property. 相似文献
9.
《Ceramics International》2022,48(5):6745-6749
A series of (Ti0.5Nb0.5)C-x wt.% SiC (x = 0, 5, 10, 20) composites were prepared by spark plasma sintering. Dense microstructures with well‐dispersed SiC particles were obtained for all composites. With the increment of SiC content, the Vickers hardness, Young's modulus and fracture toughness increase monotonically. An optimized flexural strength of 706 MPa was achieved in (Ti0.5Nb0.5)C-5 wt.%SiC composite. (Ti0.5Nb0.5)C-20 wt%SiC composite exhibits the highest fracture toughness of 6.8 MPa m1/2. The crack deflections and the suppression of grain growth were the main strengthening and toughening mechanisms. Besides, (Ti0.5Nb0.5)C-20 wt%SiC composite exhibit the highest thermal conductivity of 45 W/m·K at 800 °C. 相似文献
10.
《Journal of the European Ceramic Society》2022,42(13):5303-5313
A new high-entropy diboride (Hf0.25Zr0.25Ta0.25Sc0.25)B2 was designed to investigate the effect of introducing rare-earth metal diboride ScB2 into high-entropy diborides on its structure and properties. The local mixing enthalpy predicts that (Hf0.25Zr0.25Ta0.25Sc0.25)B2 has high enthalpy driving force, which more easily allows the formation of single-phase AlB2-type structures between components. The experiments further demonstrate that (Hf0.25Zr0.25Ta0.25Sc0.25)B2 possesses excellent phase stability, lattice integrity and nanoscale chemical homogeneity. (Hf0.25Zr0.25Ta0.25Sc0.25)B2 showed relatively high hardness (30.7 GPa), elastic modulus (E, G, and B of 522, 231 and 233 GPa, respectively), bending strength (454 MPa), and low thermal conductivity (13.9 W·m?1·K?1). The thermal expansion of (Hf0.25Zr0.25Ta0.25Sc0.25)B2 is higher than that of ZrB2 and HfB2 due to weakened bonding (M d - B p and M dd bonding) and enhanced anharmonic effects. Thus, incorporating Sc into high-entropy diborides can tailor the properties associated with the bonding, which further expands the compositional space of high-entropy diborides. 相似文献
11.
《Ceramics International》2022,48(24):36084-36090
The high-entropy ceramic materials (Zr0.25Ce0.25Hf0.25Y0.25)O1.875 (H-0) and (Zr0.2Ce0.2Hf0.2Y0.2RE0.2)O1.8 (H-RE) (RE = La, Nd and Sm) with fluorite structure and homogeneous element distribution were prepared. With fluorite structure, fine grain size and high density, the H-0 and H-RE ceramics displayed low thermal conductivity, suitable thermal expansion coefficient, high hardness and fracture toughness. The effect of La, Nd and Sm on the mechanical, heat conductivity and heat expansion properties of high entropy ceramics were discussed. The single-phase high-entropy ceramic materials in this work are very suitable for application as thermal barrier materials. 相似文献
12.
《Journal of the European Ceramic Society》1999,19(13-14):2405-2414
The thermal conductivity, thermal expansion, Youngs Modulus, flexural strength, and brittle–plastic deformation transition temperature were determined for HfB2, HfC0·98, HfC0·67, and HfN0·92 ceramics. The oxidation resistance of ceramics in the ZrB2–ZrC–SiC system was characterized as a function of composition and processing technique. The thermal conductivity of HfB2 exceeded that of the other materials by a factor of 5 at room temperature and by a factor of 2·5 at 820°C. The transition temperature of HfC exhibited a strong stoichiometry dependence, decreasing from 2200°C for HfC0·98 to 1100°C for HfC0·67 ceramics. The transition temperature of HfB2 was 1100°C. The ZrB2/ZrC/SiC ceramics were prepared from mixtures of Zr (or ZrC), SiB4, and C using displacement reactions. The ceramics with ZrB2 as a predominant phase had high oxidation resistance up to 1500°C compared to pure ZrB2 and ZrC ceramics. The ceramics with ZrB2/SiC molar ratio of 2 (25 vol% SiC), containing little or no ZrC, were the most oxidation resistant. 相似文献
13.
The properties of relaxor ceramics in the compositional series (1?x)K0.5Bi0.5TiO3–xBa(Ti0.8Zr0.2)O3 have been investigated. Values of Tm, the temperature of maximum relative permittivity, decreased from 380°C at x = 0.0 to below room temperature for x > 0.7. Compositions x = 0.1 and 0.2 were piezoelectric and ferroelectric. The maximum value of d33 piezoelectric charge coefficient, 130 pC/N, and strain, 0.14%, occurred at x = 0.1. Piezoelectric properties of x = 0.1 were retained after thermal cycling from room temperature to 220°C, consistent with results from high‐temperature X‐ray diffraction indicating a transition to single‐phase cubic at ~300°C. 相似文献
14.
Rong-Zhen Li Xin-Gang Wang Jian-Hui Yuan Xiao-Fei Wang Wei Gao Fu-Lin Qin Guo-Jun Zhang Dan-Yu Jiang 《Journal of the American Ceramic Society》2023,106(9):5440-5453
This study prepared textured (Ti1/3Zr1/3Hf1/3)B2 medium-entropy ceramics for the first time that maintain enhanced flexural strength up to 1800°C using single-phase (Ti1/3Zr1/3Hf1/3)B2 powders, slip casting under a strong magnetic field, and hot-pressed sintering methods. Effects of WC additive and strong magnetic field direction on the phase compositions, orientation degree, microstructure evolution, and high-temperature flexural strength of (Ti1/3Zr1/3Hf1/3)B2 were investigated. (Ti1/3Zr1/3Hf1/3)B2 grain grows along the a,b-axes, resulting in a platelet-like morphology. Pressure parallel and perpendicular to the magnetic field direction can promote the orientation degree and hinder the texture structure formation, respectively. Reaction products of W(B,C) and (Ti,Zr,Hf)C between (Ti1/3Zr1/3Hf1/3)B2 and WC additive can efficiently refine the (Ti1/3Zr1/3Hf1/3)B2 grain size and promote grain orientation. (Ti1/3Zr1/3Hf1/3)B2 ceramics doped with 5 vol.% WC yielded a Lotgering orientation factor of 0.74 through slip casting under a strong magnetic field (12 T) and hot-pressed sintering at 1900°C. Furthermore, cleaning the boundary by W(B,C) and introducing texture can enhance the grain-boundary strength and improve its high-temperature flexural strength. The four-point flexural strength of textured (Ti1/3Zr1/3Hf1/3)B2-5 vol.% WC ceramics was 770 ± 59 MPa at 1600°C and 638 ± 117 MPa at 1800°C. 相似文献
15.
Hua Tang Shujun Zhang Yujun Feng Fei Li Thomas R. Shrout 《Journal of the American Ceramic Society》2013,96(9):2857-2863
(1?x)Pb(Hf1?yTiy)O3–xPb(Yb0.5Nb0.5)O3 (x = 0.10–0.44, y = 0.55–0.80) ceramics were fabricated. The morphotropic phase boundary (MPB) of the ternary system was determined by X‐ray powder diffraction. The optimum dielectric and piezoelectric properties were achieved in 0.8Pb(Hf0.4Ti0.6)O3–0.2Pb(Yb0.5Nb0.5)O3 ceramics with MPB composition, where the dielectric permittivity εr, piezoelectric coefficient d33, planar electromechanical coupling kp, and Curie temperature Tc were found to be on the order of 1930,480 pC/N, 62%, and 360°C, respectively. The unipolar strain behavior was evaluated as a function of applied electric field up to 50 kV/cm to investigate the strain nonlinearity and domain wall motion under large drive field, where the high field piezoelectric d33* was found to be 620 pm/V for 0.82Pb(Hf0.4Ti0.6)O3–0.18Pb(Yb0.5Nb0.5)O3. In addition, Rayleigh analysis was carried out to study the extrinsic contribution, where the value was found to be in the range 2%–18%. 相似文献
16.
Ziming Ye Yi Zeng Xiang Xiong Tianxiao Qian Huilin Lun Yalei Wang Wei Sun Zhaoke Chen Lijun Zhang Ping Xiao 《Journal of the American Ceramic Society》2020,103(12):6978-6990
Early transition metal carbides are considered to be superior candidate materials for oxidizing environments at temperatures exceeding 2000°C. Generally, the remarkable oxidation resistance is largely attributed to a carbonaceous oxide interlayer (eg, Hf–O–C, Zr–O–C, and Ta–O–C), located at the interface between the external oxide layer and internal carbide (eg, HfC, ZrC, and TaC), acting as the primary oxygen barrier. However, the oxygen barrier mechanism of the carbonaceous oxide interlayer remains unclear. Herein, through studying the oxidation behavior of a novel multicomponent carbide Hf0.5Zr0.3Ti0.2C in oxidizing environments up to 2500°C, the oxygen barrier mechanism of the carbonaceous oxide was recently revealed. We found that the oxygen barrier resulted from the slow oxygen diffusion through the inner grains of Hf-Zr–Ti–O due to the presence of carbon formed at the grain boundaries because of the existence of compact external oxide layer, beneath which the Hf–Zr–Ti–O–C interlayer possesses much lower oxygen activity and temperature that allow carbon to exist stably. This as-formed carbon strongly retarded the fast diffusion of oxygen along the grain boundaries of oxides. Additionally, desirable synergisms of the designed multicomponent system, particularly, the outward short-circuit diffusion of Ti, lead to the self-healing of the external oxide layer, evidently enhancing integral protection performance against oxidizing environments. 相似文献
17.
Quan Sheng Yiqun Deng Tongxiang Liang Yuan Zhang 《International Journal of Applied Ceramic Technology》2022,19(5):2883-2890
A type of nonequimolar multicomponent ceramic solid solution (Mg0.5Ca0.3Ba0.2) (AlSi)2O8 with a low thermal conductivity was prepared through solid-state synthesis. Results show that the (Mg0.5Ca0.3Ba0.2) (AlSi)2O8 solid solution exhibits excellent high-temperature stability and an ultralow thermal conductivity (.3676 W m−1 K−1), far lower than widely used 3YSZ (2.9 W m−1 K−1), La3NbO7 (1.5 W m−1 K−1), and Gd2Zr2O7 (1.28 W m−1 K−1). Furthermore, the Young modulus of the final product is 64.56 GPa. Therefore, the proposed ceramic solid solution provides a new research direction for ultralow thermal conductivity materials and has a practical application value for the field of wall thermal insulation. 相似文献
18.
Duo Yu Jie Yin Buhao Zhang Xuejian Liu Michael J. Reece Wei Liu Zhengren Huang 《Journal of the European Ceramic Society》2021,41(6):3823-3831
A novel (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)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 Ta0.5Hf0.5C, (Ta1/3Zr1/3Nb1/3)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. 相似文献
19.
Yulin Zhu Song Wang Hongmei Chen Wei Li Jinming Jiang Zhaohui Chen 《Ceramics International》2013,39(8):9085-9089
Carbon fiber-reinforced zirconium carbide matrix composites (Cf/ZrC) were prepared by vacuum infiltrating porous carbon/carbon preforms with molten Zr2Cu alloy at 1200 °C. X-ray diffraction, scanning electron microcopy and transmission electron microscopy analysis were used to characterize the composition and microstructure of the final composites. It was found that the matrix of the composites were composed of the Cu–Zr–C amorphous phase dispersed with either single- or polycrystalline ZrC. Based on the microstructural analysis, the formation mechanism of the matrix was proposed to be a solution-precipitation and grain coalescence process. The influence of the heat treatment at 1800 °C was also investigated. Results indicated that at very high temperature the volatilization of residual metal somewhat deteriorated the flexural strength and the elastic modulus, but the fracture toughness of the composites was improved due to the sintering of ZrC grains. 相似文献
20.
Jiadong Zang Ming Li Derek C. Sinclair Wook Jo Jürgen Rödel 《Journal of the American Ceramic Society》2014,97(5):1523-1529
The electrical and dielectric properties of (1 ? x)(0.94Bi1/2Na1/2TiO3–0.06BaTiO3)–x(K0.5Na0.5NbO3) with x = 0, 0.03, 0.09, 0.18 have been investigated by impedance spectroscopy over a wide temperature range. The dc conductivity of the ceramics follows the Arrhenius law with an activation energy ranging from ~1.20 to 1.50 eV. Measurements under different atmospheres show the materials exhibit n‐type semiconducting behavior at elevated temperatures. The presence of a highly polarizable phase for all compositions is revealed by electric modulus (M″) spectra. The Burns temperature decreases with increasing KNN content. The change in temperature‐dependent permittivity with composition is explained by the difference in thermal evolution of polar nanoregions induced by the addition of KNN. 相似文献