Light element compounds under high pressure display intriguing properties and applications,owing to their diverse bonding patterns and crystalline structures.However,the system of ternary Be-C-O compounds under high p...Light element compounds under high pressure display intriguing properties and applications,owing to their diverse bonding patterns and crystalline structures.However,the system of ternary Be-C-O compounds under high pressure,as the lightest representative of the IIA-IVA-VIA family,remains largely unexplored.Using a machine-learning-accelerated crystal structure search and first-principles calculations,Be-C-O phase diagrams are investigated at pressures ranging from 0 to 100 GPa.Four ternary compounds are proposed to be stable at corresponding pressures:BeCO_(3),Be_(2)CO_(4),Be_(2)C_(4)O_(3),and BeC_(4)O_(2).Analyses of electronic structure and chemical bonding further reveal how the structural diversity of these compounds is induced.Remarkably,Be_(2)C_(4)O_(3) and BeC_(4)O_(2) are recoverable to ambient conditions and possess both high energy density and high hardness.The volumetric energy densities of Be_(2)C_(4)O_(3) and BeC_(4)O_(2) could approach 9.03 and 7.94 kJ/cm^(3),respectively.The Vickers hardnesses of Be_(2)C_(4)O_(3) and BeC_(4)O_(2) are found to be close to 39.58 and 51.57 GPa,respectively.These findings demonstrate the structural and functional diversity of Be-C-O compounds under high pressure,providing guidance for further exploration of the IIA-IVA-VIA compounds.展开更多
In recent years,superhard coatings have emerged as a focal point in metal material research due to their innovative design strategies and exceptional mechanical properties.They are widely utilized in industries such a...In recent years,superhard coatings have emerged as a focal point in metal material research due to their innovative design strategies and exceptional mechanical properties.They are widely utilized in industries such as shielding,oil extraction,and coal mining.However,in practical applications,tools often suffer from wear,fractures,plastic deformation,and other types of failure,directly impacting machining efficiency,costs,and product quality.To mitigate these challenges,the selection of appropriate tool materials and preparation methods is critical to ensure sustained production efficiency.Therefore,it is essential to identify and develop coating materials with superior performance.Recent advancements in superhard coatings are reviewed comprehensively;preparation methods are discussed for superhard tools;diamond coatings,diamond-like carbon coatings,cubic boron nitride coatings and graphite carbon nitride coatings are examined specifically.It analyzes their microstructures,phase transformation processes,mechanical properties,and formation mechanisms,while also evaluating properties such as wear resistance,corrosion resistance,and high hardness.The applicability of existing theoretical models is verified and new frameworks for future superhard coating designs are proposed.Moreover,the current research limitations in tool coatings are identified and directions for future research and development are proposed.展开更多
Vanadium carbide/titanium carbide （VC/TiC） superlattice films were synthesized by magnetron sputtering method. The effects of modulation period on the microstructure evolution and mechanical properties were investig...Vanadium carbide/titanium carbide （VC/TiC） superlattice films were synthesized by magnetron sputtering method. The effects of modulation period on the microstructure evolution and mechanical properties were investigated by EDXA, XRD, HRTEM and nano-indentation. The results reveal that the VC/TiC superlattice films form an epitaxial structure when their modulation period is less than a critical value, accompanied with a remarkable increase in hardness. Further increasing the modulation period, the hardness of superlattices decreases slowly to the rule-of-mixture value due to the destruction of epitaxial structures. The XRD results reveal that three-directional strains are generated in superlattices when the epitaxial structure is formed, which may change the modulus of constituent layers. This may explain the remarkable hardness enhancement of VC/TiC superlattices.展开更多
Based on the principles of massive support and lateral support, a novel double-layered split die(DLSD) for high-pressure apparatus was designed to achieve a higher pressure-bearing capacity and larger sample cavity. T...Based on the principles of massive support and lateral support, a novel double-layered split die(DLSD) for high-pressure apparatus was designed to achieve a higher pressure-bearing capacity and larger sample cavity. The stress distributions of the DLSDs with different numbers of divided blocks were investigated by the finite element method and compared with the stress distributions of the conventional belt-type die(BTD). The results show that the cylinders and first-layer supporting rings of the DLSDs have dramatically smaller stresses than those of the BTD. In addition, increasing the number of divided blocks from 4 to 10 gradually increases the stress of the cylinder but has minimal influence on the stress of the supporting rings. The pressure-bearing capacities of the DLSDs with different numbers of divided blocks, especially with fewer blocks, are all remarkably higher than the pressure-bearing capacity of the BTD. The contrast experiments were also carried out to verify the simulated results. It is concluded that the pressure-bearing capacities of the DLSDs with 4 and 8 divided blocks are 1.58 and 1.45 times greater than that of the BTD. This work is rewarding for the commercial synthesis of high-quality, large-sized superhard materials using a double-layered split high-pressure die.展开更多
This paper investigates the microstructure, physical, chemical and mechanical of superhard nanocomposite of Ti-Hf-Si-N. The coatings were grown by C-PVD method. Profiles of elements and vacancy-type defects (S-paramet...This paper investigates the microstructure, physical, chemical and mechanical of superhard nanocomposite of Ti-Hf-Si-N. The coatings were grown by C-PVD method. Profiles of elements and vacancy-type defects (S-parameter measurements of the Doppler broadening of the annihilation peak DBAP) in the studied coatings were investigated. Defined and calculated the elastic modulus E, hardness H, friction, adhesion. Wear rate was determined as a function of the bias potential supplied to the substrate and the pressure in the chamber. The developed coatings have hardness of 37.8 to 48 GPa, the friction coefficient of 0.48 to 0.15, the grain size of the solid solution from 3.9 to 10.8 nm (depending on deposition conditions). It was found that positrons are trapped by defects at the junction of three or more nanograins interfaces. In some cases, there was formed two phases in coatings: a solid solution (Ti, Hf)N with different volume content of Hf in a solid solution, and an amorphous phase α-Si3N4 (the layer between the nanograins).展开更多
The study of superhard materials plays a critical role in modern industrial applications due to their widespread applications as cutting tools, abrasives, exploitation drills, and coatings. The search for new superhar...The study of superhard materials plays a critical role in modern industrial applications due to their widespread applications as cutting tools, abrasives, exploitation drills, and coatings. The search for new superhard materials with superior performance remains a hot topic and is mainly considered as two classes of materials:(i) the light-element compounds in the B-C-N-O(-Si) system with strong and short covalent bonds, and(ii) the transition-element light-element compounds with strong covalent bonds frameworks and high valence electron density. In this paper, we review the recent achievements in the prediction of superhard materials mostly using the advanced CALYPSO methodology. A number of novel, superhard crystals of light-element compounds and transition-metal borides, carbides, and nitrides have been theoretically identified and some of them account well for the experimentally mysterious phases. To design superhard materials via CALYPSO methodology is independent of any known structural and experimental data, resulting in many remarkable structures accelerating the development of new superhard materials.展开更多
The superplasticity of high strength superhard A1 alloy LC4 was improved to a great extent by modified thermomechanical treatment.Its maximum elongation may be up to 2100% un- der deformation at initial strain rate of...The superplasticity of high strength superhard A1 alloy LC4 was improved to a great extent by modified thermomechanical treatment.Its maximum elongation may be up to 2100% un- der deformation at initial strain rate of 8.33×10^(-4) S^(-1) at 510℃.Observations of the microstructure changes revealed that with the increase of the deformation,the grain grows and the alloy exhibits strain hardening.The excellent elongation of the alloy seems due to the in- crease of grain stability under deformation.展开更多
The recent development in the field of nanocomposite coatings with good mechanical properties is critically reviewed in this paper. The design principle and materials selection for the nanocomposite coatings are intro...The recent development in the field of nanocomposite coatings with good mechanical properties is critically reviewed in this paper. The design principle and materials selection for the nanocomposite coatings are introduced. Different methods for the preparation of superhard nanocomposite coatings are described with emphasis on the magnetron sputtering. Based on recent theoretical and experimental results regarding the appearance of superhardness in nanocomposite coating, lattice parameter changes, crystallite size, microstructure and morphology are reviewed in detail. Also emphasized are the mechanical properties (especially on hardness) and the ways by which the properties are derived.展开更多
By means of density functional theory calculations, an orthogonal boron-carbon-nitrogen compound called （3,0）- BC2N is predicted, which can be obtained by transversely compressing （3,03 carbon nanotubes （CNTs） an...By means of density functional theory calculations, an orthogonal boron-carbon-nitrogen compound called （3,0）- BC2N is predicted, which can be obtained by transversely compressing （3,03 carbon nanotubes （CNTs） and boron nitride nanotubes （BNNTs）. Its structural stability, elastic properties, mechanical properties and electronic structure are systematically investigated. The results show that （3,0）-BU2N is a superhard material with a direct bandgap. However, its similar structures, （3,0）-C and （3,0）-BN are indirect semiconductors. Strikingly, （3,0）-C is harder than diamond. We also simulate the x-ray diffraction of （3,0）-BC2N to support future experimental investigations. In addition, our study shows that the transition from （3,03 CNTS and BNNTs to （3,0）-BC2N is irreversible.展开更多
In this work, a novel carbon allotrope tP40 carbon with space group P4/mmm is proposed. The structural stability, mechanical properties, elastic anisotropy, and electronic properties of tP40 carbon are investigated sy...In this work, a novel carbon allotrope tP40 carbon with space group P4/mmm is proposed. The structural stability, mechanical properties, elastic anisotropy, and electronic properties of tP40 carbon are investigated systematically by using density functional theory (DFT). The calculated elastic constants and phonon dispersion spectra indicate that the tP40 phase is a metastable carbon phase with mechanical stability and dynamic stability. The B/G ratio indicates that tP40 carbon is brittle from 0 GPa to 60 GPa, while tP40 carbon is ductile from 70 GPa to 100 GPa. Additionally, the anisotropic factors and the directional dependence of the Poisson's ratio, shear modulus, and Young's modulus of tP40 carbon at different pressures are estimated and plotted, suggesting that the tP40 carbon is elastically anisotropic. The calculated hardness values of tP40 carbon are 44.0 GPa and 40.2 GPa obtained by using Lyakhov–Oganov's model and Chen's model, respectively, which means that the tP40 carbon can be considered as a superhard material. The electronic band gap within Heyd–Scuseria–Ernzerhof hybrid functional (HSE06) is 4.130 eV, and it is found that the tP40 carbon is an indirect and wider band gap semiconductor material.展开更多
In this work,a new superhard material named Pm BN is proposed.The structural properties,stability,mechanical properties,mechanical anisotropy properties,and electronic properties of Pm BN are studied in this work.Pm B...In this work,a new superhard material named Pm BN is proposed.The structural properties,stability,mechanical properties,mechanical anisotropy properties,and electronic properties of Pm BN are studied in this work.Pm BN is dynamically and mechanically stable,the relative enthalpy of Pm BN is greater than that of c-BN,and in this respect,and it is more favorable than that of T-B_(3)N_(3),T-B_(7)N_(7),tP24 BN,Imm2 BN,Ni As BN,and rocksalt BN.The Young's modulus,bulk modulus,and shear modulus of Pm BN are 327 GPa,331 GPa,and 738 GPa,respectively,and according to Chen's model,Pm BN is a novel superhard material.Compared with its original structure,the mechanical anisotropy of Young's modulus of Pm BN is larger than that of C14 carbon.Finally,the calculations of the electronic energy band structure show that Pm BN is a semiconductor material with not only a wide band gap but also an indirect band gap.展开更多
Numerous new carbon allotropes have been uncovered by compressing carbon nanotubes based on our computational investigation. The volume compression calculations suggest that these new phases have a very high anti-comp...Numerous new carbon allotropes have been uncovered by compressing carbon nanotubes based on our computational investigation. The volume compression calculations suggest that these new phases have a very high anti-compressibility with a large bulk modulus （B0）. The predicted B0 of new phases is larger than that of c-BN （373 GPa） and smaller than that of diamond （453 GPa）. All of the predicted structures are superhard transparent materials with a larger band gap and possess the covalent characteristics with sp3-hybridized electronic states. The simulated results will help us better understand the structural phase transition of cold-compressed carbon nanotubes.展开更多
By combination of DC reactive magnetron sputter i ng with multiple arcplating,the alternating C_(3)N_(4)/TiN compo und film is deposited onto HSS.The core level binding energy and the contents o f carbon and nitrogen ...By combination of DC reactive magnetron sputter i ng with multiple arcplating,the alternating C_(3)N_(4)/TiN compo und film is deposited onto HSS.The core level binding energy and the contents o f carbon and nitrogen are characterized by X-ray photoelectron spectrum.X-ray diffraction(XRD)shows that compound thin film contains hard crystalline phases ofα-C_(3)N_(4)andβ-C_(3)N_(4).The Knoop microhardne ss in the load range of 50.5-54.1 GPa is measured.According to acoustic emissi on scratch test,the critical load values for the coatings on HSS substrates are in the range of 40-80 N.The metal coated with C_(3)N_(4)/TiN compound f ilms has a great improvement in the resistance against corrosion.Many tests sho w that such a coating has a very high wearability.Compared with the uncoated an d TiN coated tools,the C_(3)N_(4)/TiN coated tools have a much longer cut ting life.展开更多
The mechanical properties and intrinsic hardness of the α-Ga boron phase （α-Ga-B） are studied by using the combination of first-principles calculations and a semiempirieal macroscopic hardness model. It is found t...The mechanical properties and intrinsic hardness of the α-Ga boron phase （α-Ga-B） are studied by using the combination of first-principles calculations and a semiempirieal macroscopic hardness model. It is found that α- Ga-B is mechanically stable and possesses higher bulk/shear modulus as compared with γ-B28, a newly discovered high-pressure boron phase. The theoretical hardness of α-Ga-B is estimated to be 45 GPa, which is much higher than 38 GPa for γ-B28. The results strongly indicate that α-Ga-B is a potential superhard boron phase. To further obtain insight into the superhard nature of α-Ga-B, we simulate stress-strain curves under tensile and shear deformation. Meanwhile, the microscopic mechanism driving the tensile and shear deformation modes in α-Ga-B is discussed in detail.展开更多
Diamond, as the hardest known material, has been widely used in industrial applications as abrasives, coatings, and cutting and polishing tools, but it is restricted by several shortcomings, e.g., its low thermal and ...Diamond, as the hardest known material, has been widely used in industrial applications as abrasives, coatings, and cutting and polishing tools, but it is restricted by several shortcomings, e.g., its low thermal and chemical stability. Considerable efforts have been devoted to designing or synthesizing the diamond-like B-C-N-O compounds, which exhibit excellent mechanical property. In this paper, we review the recent theoretical design of diamond-like superhard structures at high pressure. In particular, the recently designed high symmetric phase of low-energy cubic BC3 meets the experimental observation, and clarifies the actual existence of cubic symmetric phase for the compounds formed by B-C-N-O system,besides the classical example of cubic boron nitride.展开更多
After a brief introduction regarding the different approaches to superhard coatings we shall concentrate on the problem of the reproducibility of the deposition of superhard and thermally very stable nanocomposites ac...After a brief introduction regarding the different approaches to superhard coatings we shall concentrate on the problem of the reproducibility of the deposition of superhard and thermally very stable nanocomposites according to the design principle published by Veprek and Reiprich in 1995. It will be shown that either the choice of inappropriate deposition conditions, in contradiction to our design principle, or impurities in the coatings are the reason for the lack of reproducibility of our earlier results by many other workers. We shall also briefly summarize the recent industrial applications.展开更多
Tool protective films operate under extreme service conditions,requiring exceptional hardness.Transition metal diborides(TMB_(2)),with strong covalent TM–B and B–B bonds,are promising candidates,but achieving superh...Tool protective films operate under extreme service conditions,requiring exceptional hardness.Transition metal diborides(TMB_(2)),with strong covalent TM–B and B–B bonds,are promising candidates,but achieving superhardness while preserving their simple binary structure remains challenging.Here,we use HfB_(2) as a model system to reveal how boron vacancy filling and in-plane compressive stress synergistically enhance hardness,through combined experimental synthesis and first-principles calculations.(001)-oriented HfB_(2) thin films were fabricated,including sub-stoichiometric HfB_(2−x),stoichiometric HfB_(2),and stoichiometric HfB_(2) under compressive stress.Nanoindentation shows the hardness increases from 33.0±1.1 GPa in HfB_(1.90) to 40.5±0.4 GPa in stoichiometric HfB_(2),and further to 45.7±1.1 GPa under−3.67 GPa stress.Calculations reveal that vacancy filling increases the number of load-bearing bonds and strengthens B–B bonding via charge accumulation,while compressive stress shortens B–B bonds to further enhance their strength.These findings clarify the atomic-scale mechanisms of vacancy and stress engineering in TMB_(2),and propose a simple,scalable pathway to superhard protective films without alloying or doping,addressing a long-standing challenge in coatings for extreme environments.展开更多
基金supported by the National Key R&D Program of China(Grant Nos.2018YFA0703404 and 2017YFA0403704)the National Natural Science Foundation of China(Grant Nos.11774121 and 91745203)the Program for Changjiang Scholars and Innovative Research Team in University(Grant No.IRT_15R23).
文摘Light element compounds under high pressure display intriguing properties and applications,owing to their diverse bonding patterns and crystalline structures.However,the system of ternary Be-C-O compounds under high pressure,as the lightest representative of the IIA-IVA-VIA family,remains largely unexplored.Using a machine-learning-accelerated crystal structure search and first-principles calculations,Be-C-O phase diagrams are investigated at pressures ranging from 0 to 100 GPa.Four ternary compounds are proposed to be stable at corresponding pressures:BeCO_(3),Be_(2)CO_(4),Be_(2)C_(4)O_(3),and BeC_(4)O_(2).Analyses of electronic structure and chemical bonding further reveal how the structural diversity of these compounds is induced.Remarkably,Be_(2)C_(4)O_(3) and BeC_(4)O_(2) are recoverable to ambient conditions and possess both high energy density and high hardness.The volumetric energy densities of Be_(2)C_(4)O_(3) and BeC_(4)O_(2) could approach 9.03 and 7.94 kJ/cm^(3),respectively.The Vickers hardnesses of Be_(2)C_(4)O_(3) and BeC_(4)O_(2) are found to be close to 39.58 and 51.57 GPa,respectively.These findings demonstrate the structural and functional diversity of Be-C-O compounds under high pressure,providing guidance for further exploration of the IIA-IVA-VIA compounds.
基金financially supported by the National Natural Science Foundation of China(No.52475347)the National Program of Foreign Experts of China(No.G2023026003L)+3 种基金the High-end Foreign Experts Introduction Project of Henan Province,China(No.HNGD2025026)Project supported by the Program for the Top Young Talents of Henan Province,China,Project(No.242102521057)sponsored by the International Science and Technology Cooperation Project of Henan Province,China,and projects supported by China Postdoctoral Foundation(No.2023M740475)Henan Provincial Science and Technology R&D Joint Fund(Industry)(No.225101610002).
文摘In recent years,superhard coatings have emerged as a focal point in metal material research due to their innovative design strategies and exceptional mechanical properties.They are widely utilized in industries such as shielding,oil extraction,and coal mining.However,in practical applications,tools often suffer from wear,fractures,plastic deformation,and other types of failure,directly impacting machining efficiency,costs,and product quality.To mitigate these challenges,the selection of appropriate tool materials and preparation methods is critical to ensure sustained production efficiency.Therefore,it is essential to identify and develop coating materials with superior performance.Recent advancements in superhard coatings are reviewed comprehensively;preparation methods are discussed for superhard tools;diamond coatings,diamond-like carbon coatings,cubic boron nitride coatings and graphite carbon nitride coatings are examined specifically.It analyzes their microstructures,phase transformation processes,mechanical properties,and formation mechanisms,while also evaluating properties such as wear resistance,corrosion resistance,and high hardness.The applicability of existing theoretical models is verified and new frameworks for future superhard coating designs are proposed.Moreover,the current research limitations in tool coatings are identified and directions for future research and development are proposed.
基金Project(51201187)supported by the National Natural Science Foundation of China
文摘Vanadium carbide/titanium carbide （VC/TiC） superlattice films were synthesized by magnetron sputtering method. The effects of modulation period on the microstructure evolution and mechanical properties were investigated by EDXA, XRD, HRTEM and nano-indentation. The results reveal that the VC/TiC superlattice films form an epitaxial structure when their modulation period is less than a critical value, accompanied with a remarkable increase in hardness. Further increasing the modulation period, the hardness of superlattices decreases slowly to the rule-of-mixture value due to the destruction of epitaxial structures. The XRD results reveal that three-directional strains are generated in superlattices when the epitaxial structure is formed, which may change the modulus of constituent layers. This may explain the remarkable hardness enhancement of VC/TiC superlattices.
基金Changchun Ruiguang Science & Technology Co., Ltd. for technical assistance and financial support
文摘Based on the principles of massive support and lateral support, a novel double-layered split die(DLSD) for high-pressure apparatus was designed to achieve a higher pressure-bearing capacity and larger sample cavity. The stress distributions of the DLSDs with different numbers of divided blocks were investigated by the finite element method and compared with the stress distributions of the conventional belt-type die(BTD). The results show that the cylinders and first-layer supporting rings of the DLSDs have dramatically smaller stresses than those of the BTD. In addition, increasing the number of divided blocks from 4 to 10 gradually increases the stress of the cylinder but has minimal influence on the stress of the supporting rings. The pressure-bearing capacities of the DLSDs with different numbers of divided blocks, especially with fewer blocks, are all remarkably higher than the pressure-bearing capacity of the BTD. The contrast experiments were also carried out to verify the simulated results. It is concluded that the pressure-bearing capacities of the DLSDs with 4 and 8 divided blocks are 1.58 and 1.45 times greater than that of the BTD. This work is rewarding for the commercial synthesis of high-quality, large-sized superhard materials using a double-layered split high-pressure die.
文摘This paper investigates the microstructure, physical, chemical and mechanical of superhard nanocomposite of Ti-Hf-Si-N. The coatings were grown by C-PVD method. Profiles of elements and vacancy-type defects (S-parameter measurements of the Doppler broadening of the annihilation peak DBAP) in the studied coatings were investigated. Defined and calculated the elastic modulus E, hardness H, friction, adhesion. Wear rate was determined as a function of the bias potential supplied to the substrate and the pressure in the chamber. The developed coatings have hardness of 37.8 to 48 GPa, the friction coefficient of 0.48 to 0.15, the grain size of the solid solution from 3.9 to 10.8 nm (depending on deposition conditions). It was found that positrons are trapped by defects at the junction of three or more nanograins interfaces. In some cases, there was formed two phases in coatings: a solid solution (Ti, Hf)N with different volume content of Hf in a solid solution, and an amorphous phase α-Si3N4 (the layer between the nanograins).
基金Project supported by the National Key Research and Development Program of China(Grant No.2018YFA0703400)the National Natural Science Foundation of China(Grant Nos.51722209,51572235,and 51672238)+2 种基金the 100 Talents Plan of Hebei Province of China(Grant No.E2016100013)the NSF for Distinguished Young Scholars of Hebei Province of China(Grant No.E2018203349)the Key Research and Development Program of Hebei Province of China(Grant No.17211110D)
文摘The study of superhard materials plays a critical role in modern industrial applications due to their widespread applications as cutting tools, abrasives, exploitation drills, and coatings. The search for new superhard materials with superior performance remains a hot topic and is mainly considered as two classes of materials:(i) the light-element compounds in the B-C-N-O(-Si) system with strong and short covalent bonds, and(ii) the transition-element light-element compounds with strong covalent bonds frameworks and high valence electron density. In this paper, we review the recent achievements in the prediction of superhard materials mostly using the advanced CALYPSO methodology. A number of novel, superhard crystals of light-element compounds and transition-metal borides, carbides, and nitrides have been theoretically identified and some of them account well for the experimentally mysterious phases. To design superhard materials via CALYPSO methodology is independent of any known structural and experimental data, resulting in many remarkable structures accelerating the development of new superhard materials.
文摘The superplasticity of high strength superhard A1 alloy LC4 was improved to a great extent by modified thermomechanical treatment.Its maximum elongation may be up to 2100% un- der deformation at initial strain rate of 8.33×10^(-4) S^(-1) at 510℃.Observations of the microstructure changes revealed that with the increase of the deformation,the grain grows and the alloy exhibits strain hardening.The excellent elongation of the alloy seems due to the in- crease of grain stability under deformation.
文摘The recent development in the field of nanocomposite coatings with good mechanical properties is critically reviewed in this paper. The design principle and materials selection for the nanocomposite coatings are introduced. Different methods for the preparation of superhard nanocomposite coatings are described with emphasis on the magnetron sputtering. Based on recent theoretical and experimental results regarding the appearance of superhardness in nanocomposite coating, lattice parameter changes, crystallite size, microstructure and morphology are reviewed in detail. Also emphasized are the mechanical properties (especially on hardness) and the ways by which the properties are derived.
基金Supported by the National Natural Science Foundation of China under Grant No 11464028the Science Foundation of Department of Education of Jiangxi Province under Grant No GJJ150025
文摘By means of density functional theory calculations, an orthogonal boron-carbon-nitrogen compound called （3,0）- BC2N is predicted, which can be obtained by transversely compressing （3,03 carbon nanotubes （CNTs） and boron nitride nanotubes （BNNTs）. Its structural stability, elastic properties, mechanical properties and electronic structure are systematically investigated. The results show that （3,0）-BU2N is a superhard material with a direct bandgap. However, its similar structures, （3,0）-C and （3,0）-BN are indirect semiconductors. Strikingly, （3,0）-C is harder than diamond. We also simulate the x-ray diffraction of （3,0）-BC2N to support future experimental investigations. In addition, our study shows that the transition from （3,03 CNTS and BNNTs to （3,0）-BC2N is irreversible.
基金Project supported by the National Natural Science Foundationof China(Grant Nos.61804120 and 61901162)the China Postdoctoral Science Foundation(Grant Nos.2019TQ0243 and 2019M663646)+2 种基金the Young Talent Fund of University Association for Science and Technology in Shaanxi Province,China(Grant No.20190110)the National Key Research and Development Program of China(Grant No.2018YFB1502902)the Key Program for International Science and Technolog Cooperation Projects of Shaanxi Province,China(Grant No.2019KWZ-03).
文摘In this work, a novel carbon allotrope tP40 carbon with space group P4/mmm is proposed. The structural stability, mechanical properties, elastic anisotropy, and electronic properties of tP40 carbon are investigated systematically by using density functional theory (DFT). The calculated elastic constants and phonon dispersion spectra indicate that the tP40 phase is a metastable carbon phase with mechanical stability and dynamic stability. The B/G ratio indicates that tP40 carbon is brittle from 0 GPa to 60 GPa, while tP40 carbon is ductile from 70 GPa to 100 GPa. Additionally, the anisotropic factors and the directional dependence of the Poisson's ratio, shear modulus, and Young's modulus of tP40 carbon at different pressures are estimated and plotted, suggesting that the tP40 carbon is elastically anisotropic. The calculated hardness values of tP40 carbon are 44.0 GPa and 40.2 GPa obtained by using Lyakhov–Oganov's model and Chen's model, respectively, which means that the tP40 carbon can be considered as a superhard material. The electronic band gap within Heyd–Scuseria–Ernzerhof hybrid functional (HSE06) is 4.130 eV, and it is found that the tP40 carbon is an indirect and wider band gap semiconductor material.
基金supported by the National Natural Science Foundation of China(Grant No.61804120)China Postdoctoral Science Foundation(Nos.2019TQ0243,2019M663646)+4 种基金Natural Science Basic Research Program of Shaanxi(2021JQ-515)Key scientific research plan of Education Department of Shaanxi Provincial Government(Key Laboratory Project)(No.20JS066)Young Talent fund of University Association for Science and Technology in Shaanxi,China(No.20190110)National Key Research and Development Program of China(No.2018YFB1502902)Key Program for International S&T Cooperation Projects of Shaanxi Province(No.2019KWZ-03)。
文摘In this work,a new superhard material named Pm BN is proposed.The structural properties,stability,mechanical properties,mechanical anisotropy properties,and electronic properties of Pm BN are studied in this work.Pm BN is dynamically and mechanically stable,the relative enthalpy of Pm BN is greater than that of c-BN,and in this respect,and it is more favorable than that of T-B_(3)N_(3),T-B_(7)N_(7),tP24 BN,Imm2 BN,Ni As BN,and rocksalt BN.The Young's modulus,bulk modulus,and shear modulus of Pm BN are 327 GPa,331 GPa,and 738 GPa,respectively,and according to Chen's model,Pm BN is a novel superhard material.Compared with its original structure,the mechanical anisotropy of Young's modulus of Pm BN is larger than that of C14 carbon.Finally,the calculations of the electronic energy band structure show that Pm BN is a semiconductor material with not only a wide band gap but also an indirect band gap.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11174242,11204265,11404278,11147007,and 11274151)the Natural Science Foundation of Jiangsu Province,China(Grant No.BK2012248)the Scientific Research Foundation of Yancheng Institute of Technology,China(Grant No.KJC2014024)
文摘Numerous new carbon allotropes have been uncovered by compressing carbon nanotubes based on our computational investigation. The volume compression calculations suggest that these new phases have a very high anti-compressibility with a large bulk modulus （B0）. The predicted B0 of new phases is larger than that of c-BN （373 GPa） and smaller than that of diamond （453 GPa）. All of the predicted structures are superhard transparent materials with a larger band gap and possess the covalent characteristics with sp3-hybridized electronic states. The simulated results will help us better understand the structural phase transition of cold-compressed carbon nanotubes.
基金Supported by the National Natural Science Foun-dation of China(19875037)
文摘By combination of DC reactive magnetron sputter i ng with multiple arcplating,the alternating C_(3)N_(4)/TiN compo und film is deposited onto HSS.The core level binding energy and the contents o f carbon and nitrogen are characterized by X-ray photoelectron spectrum.X-ray diffraction(XRD)shows that compound thin film contains hard crystalline phases ofα-C_(3)N_(4)andβ-C_(3)N_(4).The Knoop microhardne ss in the load range of 50.5-54.1 GPa is measured.According to acoustic emissi on scratch test,the critical load values for the coatings on HSS substrates are in the range of 40-80 N.The metal coated with C_(3)N_(4)/TiN compound f ilms has a great improvement in the resistance against corrosion.Many tests sho w that such a coating has a very high wearability.Compared with the uncoated an d TiN coated tools,the C_(3)N_(4)/TiN coated tools have a much longer cut ting life.
基金Supported by the National Natural Science Foundation of China under Grant Nos 21303156,21201148,210303156 and 21403185the Natural Science Foundation of Hebei Province under Grant Nos B2011203121 and B2012203005
文摘The mechanical properties and intrinsic hardness of the α-Ga boron phase （α-Ga-B） are studied by using the combination of first-principles calculations and a semiempirieal macroscopic hardness model. It is found that α- Ga-B is mechanically stable and possesses higher bulk/shear modulus as compared with γ-B28, a newly discovered high-pressure boron phase. The theoretical hardness of α-Ga-B is estimated to be 45 GPa, which is much higher than 38 GPa for γ-B28. The results strongly indicate that α-Ga-B is a potential superhard boron phase. To further obtain insight into the superhard nature of α-Ga-B, we simulate stress-strain curves under tensile and shear deformation. Meanwhile, the microscopic mechanism driving the tensile and shear deformation modes in α-Ga-B is discussed in detail.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51202084,11474125,and 51372095)
文摘Diamond, as the hardest known material, has been widely used in industrial applications as abrasives, coatings, and cutting and polishing tools, but it is restricted by several shortcomings, e.g., its low thermal and chemical stability. Considerable efforts have been devoted to designing or synthesizing the diamond-like B-C-N-O compounds, which exhibit excellent mechanical property. In this paper, we review the recent theoretical design of diamond-like superhard structures at high pressure. In particular, the recently designed high symmetric phase of low-energy cubic BC3 meets the experimental observation, and clarifies the actual existence of cubic symmetric phase for the compounds formed by B-C-N-O system,besides the classical example of cubic boron nitride.
文摘After a brief introduction regarding the different approaches to superhard coatings we shall concentrate on the problem of the reproducibility of the deposition of superhard and thermally very stable nanocomposites according to the design principle published by Veprek and Reiprich in 1995. It will be shown that either the choice of inappropriate deposition conditions, in contradiction to our design principle, or impurities in the coatings are the reason for the lack of reproducibility of our earlier results by many other workers. We shall also briefly summarize the recent industrial applications.
基金supported by the National Natural Science Foundation of China(52322206,524B2014)the National Key Research and Development Program of China(2023YFF0716800)the High-Performance Computing Center of Jilin University,China。
文摘Tool protective films operate under extreme service conditions,requiring exceptional hardness.Transition metal diborides(TMB_(2)),with strong covalent TM–B and B–B bonds,are promising candidates,but achieving superhardness while preserving their simple binary structure remains challenging.Here,we use HfB_(2) as a model system to reveal how boron vacancy filling and in-plane compressive stress synergistically enhance hardness,through combined experimental synthesis and first-principles calculations.(001)-oriented HfB_(2) thin films were fabricated,including sub-stoichiometric HfB_(2−x),stoichiometric HfB_(2),and stoichiometric HfB_(2) under compressive stress.Nanoindentation shows the hardness increases from 33.0±1.1 GPa in HfB_(1.90) to 40.5±0.4 GPa in stoichiometric HfB_(2),and further to 45.7±1.1 GPa under−3.67 GPa stress.Calculations reveal that vacancy filling increases the number of load-bearing bonds and strengthens B–B bonding via charge accumulation,while compressive stress shortens B–B bonds to further enhance their strength.These findings clarify the atomic-scale mechanisms of vacancy and stress engineering in TMB_(2),and propose a simple,scalable pathway to superhard protective films without alloying or doping,addressing a long-standing challenge in coatings for extreme environments.
