Numerical simulation and experimental verification of a novel double-layered split die for high-pressure apparatus used for synthesizing superhard materials

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.

Investigation of Element Profiles, Defects, Phase Composition and Physical and Mechanical Properties of Superhard Coatings Ti-Hf-Si-N

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).

Discovery of superhard materials via CALYPSO methodology

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.

SUPERPLASTIC DEFORMATION BEHAVIOR OF SUPERHARD Al ALLOY LC4

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.

Research on C_3N_4 Superhard Compound Thin Film and Its Application

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 of α \|C 3 N 4 and β \|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.

Superhard BC_2N:an Orthogonal Crystal Obtained by Transversely Compressing(3,0)-CNTs and(3,0)-BNNTs

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.

Reproducibility of deposition and industrial applications of stable superhard nanocomposites

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.

tP40 carbon: A novel superhard carbon allotrope

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.

Low-temperature phase transformation from nanotube to sp^3 superhard carbon phase

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.

First Principles Study on Mechanical Properties of Superhard α-Ga Boron

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.

Theoretical design of diamondlike superhard structures at high pressure

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.

Synthesis and nitrogen content regulation of diamond in a high-pressure hydrogen-rich environment

The regulating nitrogen content of diamond in a hydrogen-rich high-temperature and high-pressure(HPHT) growth environment was systematically investigated in this work by developing three growth systems,namely, "FeNi+Ti", "FeNi+G_(3)N_(6)H_(6)",and "FeNi+Ti+C_(3)N_(6)H_(6)".Optical microscopy,infrared spectroscopy,and photoluminescence(PL)spectroscopy measurements were conducted to analyze the spectroscopic characteristics of diamonds grown in these three systems.From our analysis,it was demonstrated that the presence of hydrogen in the sp^(3) hybrid C-H does not directly affect the color of the diamond and facilitates the increase of the nitrogen-vacancy(NV) center concentration in a highnitrogen-content diamond.In addition,titanium plays an important role in nitrogen removal,while its impact on hydrogen doping within the diamond lattice is insignificant.Most importantly,by regulating the ratio of nitrogen impurities that coexist in the nitrogen and hydrogen HPHT environment,the production of hydrogenous Ⅱa-type diamond,hydrogenous Ib-type diamond,and hydrogenous high-nitrogen-type diamonds was achieved with a nitrogen content of less than 1 ppm to 1600 ppm.

基于金刚石热历史的超硬磨具激光增材制造工艺与组织性能优化

超硬磨具激光增材制造过程中,金刚石极易受到激光直接辐照和高温熔池的影响,出现石墨化等热损伤现象.选取典型的金刚石磨具用金属结合剂CuSn10粉末,采用粉末床熔融(Powder Bed Fusion-laser Beam,PBF-LB)技术制备CuSn10-金刚石复合材料;围绕高能激光束和高温熔池两个影响增材制造过程中金刚石颗粒性能的关键因素,以单颗金刚石颗粒为研究对象,通过有限元模拟分析构建金刚石颗粒的温度场模型,反映了金刚石颗粒在PBF-LB中的热演化过程;阐明了PBF-LB过程金刚石的热损伤机制,发现金刚石发生石墨化转变并不是由激光的直接辐照造成的,而是由高温熔池的热影响导致,CuSn10-金刚石复合材料在PBF-LB过程中石墨化的临界温度为1491.6℃.建立了PBF-LB工艺-金刚石颗粒温度-石墨化程度-摩擦磨损性能的定量关系,发现随着金刚石颗粒温度的增加,其石墨化程度增加,严重损害了复合材料的摩擦磨损性能.

超硬材料在地质钻探中的应用与发展

超硬材料和钻探工程有着密不可分的联系,目前已成为钻探行业的重点研发材料。超硬材料在推动钻探行业向深井、超深井领域发展方面发挥了至关重要的作用。本文以金刚石、立方氮化硼和复合超硬材料为基础,介绍了超硬材料的分类及其特点。随后对钻探行业中超硬材料产品的应用和发展进行了详述,并分析钻探行业对超硬材料的需求,进而对其未来发展趋势进行展望,以期能为超硬材料在地质钻探领域的应用与发展起一定的指导作用。

PCD/PcBN超硬刀片的刃磨

近几十年,超硬刀片被广泛应用于汽车制造、3C电子等要求刀具寿命长、生产节拍高的领域。这也对超硬刀片的批量化生产提出了更高的要求。本文对超硬刀具及材料特性、制作工艺与特点进行了探究,介绍了超硬刀片刃磨的三种加工方式,尤其对机械磨削方式进行了深入探讨,在中小批量人工刃磨的工艺基础上,创造和研发了自动化无人值守生产所需的刃磨工艺及算法,并融入其自动化机床产品当中。

A novel superhard boron nitride polymorph with monoclinic symmetry

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.

A novel superhard tungsten nitride predicted by machine-learning accelerated crystal structure search

Transition metal nitrides have been suggested to have both high hardness and good thermal stability with large potential application value,but so far stable superhard transition metal nitrides have not been synthesized.Here,with our newly developed machine-learning accelerated crystal structure searching method,we designed a superhard tungsten nitride,h-WN_6,which can be synthesized at pressure around65 GPa and quenchable to ambient pressure.This h-WN_6is constructed with single-bonded armchair-like N_6rings and presents ionic-like features,which can be formulated as W^(2.4+)N_6^(2.4à).It has a band gap of1.6 e V at 0 GPa and exhibits an abnormal gap broadening behavior under pressure.Excitingly,this h-WN_6is found to be the hardest among transition metal nitrides known so far(Vickers hardness around57 GPa)and also has a very high melting temperature(around 1,900 K).Additionally,the good gravimetric(3.1 k J/g)and volumetric(28.0 k J/cm^3)energy densities make this nitrogen-rich compound a potential high-energy-density material.These predictions support the designing rules and may stimulate future experiments to synthesize superhard and high-energy-density material.