Superhard Research Articles

Effects of twin thickness, strain rate, and temperature on the mechanical properties of nanotwinned diamond

Nanotwinned (NT) diamond is a superior ceramic material known for its extreme hardness and strength. Both intrinsic and extrinsic factors strongly affect the mechanical properties of NT diamond. Here, we perform molecular dynamics (MD) simulations to study the mechanical properties of NT diamond under uniaxial tension, emphasizing the effects of twin thickness, strain rate, and temperature. The structural evolution, crack initiation and propagation, and scaling laws of strength and toughness are studied. Our findings reveal that a higher number of branching cracks enhance the mechanical properties of NT diamond, particularly when compared to single-crystal diamond. The presence of twin structures alters the orientation of diamond atoms, changing the direction of crack propagation and resulting in increased branching cracks upon fracture. Within constrained geometries, a “thinner is stronger” trend is observed concerning twin thickness. Our quantitative analysis further shows that mechanical properties decline with decreasing strain rates and increasing temperatures. This strain rate effect is attributed to the relaxation of residual stress, where the released energy compensates for the formation of new surfaces. We also provide a predictive model for the mechanical properties of NT diamond, offering valuable insights for the development of high-performance NT superhard materials.

First-principles study of influence of transition metal doping on the physical properties of TiB3

Superhard materials possess a multitude of advantageous properties and are utilized in a plethora of fields. The calculated hardness of TiB3 is 41.6 GPa and those of all TM-doped TiB3 are higher than 40 GPa, thereby indicating that TiB3 and TM-doped TiB3 are potential superhard materials. This paper presents a comprehensive study of the electronic, elastic and thermal properties, fracture toughness and damage tolerance of TiB3 and its doped transition metals (TMs, including Sc, V, Y, Zr, Nb, Hf and Ta) through the use of first-principles calculations. These materials are thermodynamically, kinetically and mechanically stable, as evidenced by the dispersion of phonon and Debye temperature. Furthermore, calculations were performed to determine the impact of doping on the brittleness and toughness of the materials, with specific attention paid to hardness, fracture toughness and elastic modulus. The anisotropy of the doped material is analysed through the projection of the 3D surface structure and the 2D Young's modulus. The metallic nature of these materials is revealed by energy band structure and density of states analyses. Finally, the effect of doping on the thermodynamic properties of the materials is explored by means of Debye temperature and sound velocity evaluations.

Novel superhard orthorhombic O12 carbon: a first principle study

Abstract In this study, a new orthorhombic carbon structure with Ama2 symmetry, designated as O12 carbon, has been predicted on basis of the first-principles method. The thermal stability and dynamic stability of O12 carbon were evaluated and confirmed by combining ab initio molecular dynamics and phonon spectra analyses. Meanwhile, the mechanical properties of O12 carbon, compared with other superhard carbon allostrope like diamond, M-carbon, Bct-c4 and Cco-C8, have also been systematically investigated. With a bulk modulus of 351 GPa, a shear modulus of 333 GPa, and a Vickers hardness of 53 GPa, O12 carbon is identified as a superhard material of significantly technological and industrial applications. The existence of elastic anisotropy in O12 carbon has also been confirmed. The electronic band structure calculations have revealed that O12 carbon exhibits a semiconductor characteristic with a direct band gap of 2.5 eV, making it promising candidate in electronic applications. Additionally, the XRD spectra of O12 carbon were obtained to offer further insights for potential experimental observations. Our findings enrich the family of carbon structure and are expected to stimulate additional experimental interest.

Enhanced compressive strength by Ti[sbnd]Cr coating on cBN particle surface using vacuum vapor deposition

In order to enhance compressive strength of the coating on cBN particles, this study proposes using vacuum vapor deposition to achieve a Titanium-Chromium (TiCr) co-deposited coating on the surface of cBN particles. Base on deposition process of the TiCr coating using vacuum vapor deposition technology, it proposed a simulation model by an Angular Coefficient Method(ACM), and conducts compressive strength experiments on the TiCr coating of cBN particles. Using the simulation and analysis model, the effect of temperature on the formation of TiCr coating during the reaction process was systematically analyzed, the molecular flow, the change of film thickness, and the deposition rate at different temperature stages was got, and verify the simulation results through experiments. The formation mechanism of TiCr co-deposited coatings was derived by SEM, XRD characterization and reaction thermodynamic analysis. Experiments show that TiCr co-deposited coatings are effective in increasing compressive strength, and the experimental results can be a guidance in controlling Ti/Cr amount in the coatings. In addition, it was found in experiments that by using vacuum vapor deposition technique, Ti/Cr powder mixing ratio of 1:1 provided the best compressive strength, and the compressive strength increased with higher Cr content in the coating after heating. This achievement is of significant importance for the formation of alloyed coatings on superhard materials, enhancing the wettability between the surfaces of superhard materials and their substrates under high-temperature conditions.

Transforming Nanocrystals into Superhard Boron Carbide Nanostructures.

Boron carbide (B4+δC) possesses a large potential as a structural material owing to its lightness, refractory character, and outstanding mechanical properties. However, its large-scale industrialization is set back by its tendency to amorphize when subjected to an external stress. In the present work, we design a path toward nanostructured boron carbide with greatly enhanced hardness and resistance to amorphization. The reaction pathway consists of triggering an isomorphic transformation of covalent nanocrystals of Na1-xB5-xC1+x (x = 0.18) produced in molten salts. The resulting 10 nm B4.1C nanocrystals exhibit a 4-fold decrease of size compared to previous works. Solid-state 11B and 13C NMR coupled to density functional theory (DFT) reveal that the boron carbide nanocrystals are made of a complex mixture of atomic configurations, which are located at the covalent structural chains between B11C icosahedral building units. These nanocrystals are combined with a spark plasma-sintering-derived method operated at high pressure. This yields full densification while maintaining the particle size. The nanoscaled grains and high density of grain boundaries provide the resulting nanostructured bodies with significantly enhanced hardness and resistance to amorphization, thus delivering a superhard material.

Predicting potential hard materials in Nb[sbnd]B ternary boride: First-principles calculations

To identify potential superhard materials, we conducted a comprehensive theoretical investigation of the thermodynamic and kinetic stability, mechanical properties, electronic structure, Debye temperatures and melting point of sixteen ternary transition metal borides NbTMBx (x = 1, 2, 4 and TM = Ti, V, Fe, Co, Ni, Zr, Ru, Hf, W, Os) using first-principles methods. Our findings indicate that, with the exception of NbFeB, NbRuB, and NbWB, all other borides exhibit both thermodynamic and kinetic stability. Notably, NbTiB4, NbVB4, NbZrB4 and NbHfB4 demonstrate superior hardness and enhanced resistance to deformation, with NbTiB4 showing an impressive hardness value of 40.84 GPa, positioning it as a promising candidate for superhard materials. Both NbVB4 and NbTiB4 have very high Debye temperatures and melting points and can be used in high temperature environments. We further explored the mechanical properties of NbTiB4 at elevated temperatures by employing a combination of first-principles and quasi-static methods. Our analysis reveals that the elastic constants and moduli of NbTiB4 decrease with increasing temperature. Additionally, bonding analysis indicates that all NbB ternary borides exhibit hybridization involving metallic, ionic, and covalent interactions, resulting in the formation of exceptionally strong covalent bonds between boron atoms.

Heterogeneous Structured Nanomaterials from Carbon and Related Materials

AbstractHeterogeneous structured nanomaterials can be considered as a class of advanced materials that integrate multiple phases, different elements, or components into a single nanoscale structure. For such materials, the different phases, components and their interactions are highly variable and tunable, which open a new avenue for the creation of new materials with unique properties unattainable by the corresponding single‐phase materials. In this review, heterogeneous structured nanomaterials constructed by different carbon allotropes are focused. Due to the unique bonding ability of carbon element, the diverse heterogeneous structures constructed by carbon structures with different dimensions possess distinctive structures and exhibit fascinating properties, providing unprecedented opportunities for various application fields, including electronic/optoelectronic devices, superhard materials, etc. This review provides a systematic elaboration for carbon‐based heterogeneous structured nanomaterials, highlighting their dimension‐dependent structural diversity, unique properties, and application prospects.

Hydrogen-Doped c-BN as a Promising Path to High-Temperature Superconductivity Above 120 K at Ambient Pressure.

Finding high-temperature superconductivity in light-weight element containing compounds at atmosphere pressure is currently a research hotspot but has not been reached yet. Here it is proposed that hard or superhard materials can be promising candidates to possess the desirable high-temperature superconductivity. By studying the electronic structures and superconducting properties of H and Li doped c-BN within the framework of the first-principles, it is demonstrated that the doped c-BN are indeed good superconductors at ambient pressure after undergoing the phase transition from the insulating to metallic behavior, though holding different nature of metallization. Li doped c-BN is predicted to exhibit the superconducting transition temperature of ≈58 K, while H doped c-BN has stronger electron-phonon interaction and possesses a higher transition temperature of 122 K. These results and findings thus point out a new direction for exploring the ambient-pressure higher-temperature superconductivity in hard or superhardmaterials.

Boron Oxide on the Surface of Grains from Superhard Materials as a Possible Factor Increasing the Performance Characteristics of Grinding Tools

Boron Oxide on the Surface of Grains from Superhard Materials as a Possible Factor Increasing the Performance Characteristics of Grinding Tools

Quantum confinement effect in nanotwinned diamond

The success in enhancing diamond by introducing nanotwins opens a new frontier in the development of superhard materials. However, the underlying hardening mechanism of nanotwinned diamond (nt-diamond) remains elusive and a persistent research focus. In this study, we employ first-principles calculations to unveil the performance enhancement in nt-diamond mediated by quantum confinement effect. This effect is characterized by the non-uniform valence charge density of C-C bonds near the twin boundary, leading to incomplete bond breakage at the onset of elastic instability and identified as the key factor in delaying cracking. These findings not only contribute to establishing the theory of hardness in superhard materials, but also suggest new avenues for enhancing their mechanical performance through the introduction of heterogeneous structures and dopant atoms aligned with the principle of quantum confinement effect.

Two novel carbon allotropes with exceptional properties as superhard materials

Scientific researchers are always working to study carbon allotropes, which are considered significant objectives. In this study, we identified two novel high-pressure carbon materials, named C14-c and C14-p, respectively, both of which demonstrate excellent performance across several physical parameters. At the same time, we proved their stability in dynamics and mechanics by calculating their phonon spectrum and elastic constants, and determined some of their physical attributes using formula calculations. Ultimately, we conducted research and performed calculations on the pertinent physical characteristics of the structure. As a result, we reached the conclusion that the band gap at 0 pressure for both structures is 3.75 eV and 3.89 eV, respectively, indicating that they are both insulators. Their enthalpy values are somewhat greater than that of diamond, but lower than the enthalpy values of the majority of known carbon allotropes. With a hardness of 81 GPa, these materials outperform many carbon structures and are considered typical superhard materials, but they do not quite approach the hardness of diamond. Their Young's modulus is anisotropic, but is isotropic on certain crystallographic planes. The thermal conductivity at room temperature is 1.725 W/cmK−1 and 1.730 W/cmK−1, respectively, both of which greater than that of diamond, illustrating that they have promising characteristics as semiconductor materials under certain high-pressure conditions.

Research on the Application of Superhard Coating Technology for Cutting Tools in Mechanical Processing

The superhard coating technology for cutting tools has important applications in the field of mechanical processing. This article introduces the development of superhard coating materials for cutting tools, including low-pressure gas-phase synthesis of diamond, cubic boron nitride, and physical vapor deposition (PVD) coating technology. The superhard coating of cutting tools is widely used in turning, milling, tapping, key component machining, high-speed steel drill bits and taps. Research has shown that coatings can reduce cutting forces and improve tool life, but attention should be paid to residual compressive stress. The future development direction includes researching new superhard material cutting tools and developing coating methods that are more wear-resistant and have high temperature hardness.

Evaluation of cobalt removal from polycrystalline diamond compact in the coupling mechanism of acid leaching and electrolysis

Polycrystalline diamond compact (PDC) is a widely used superhard material, and its thermal stability and wear resistance are the main factors determining its performance. The residual cobalt binder content in polycrystalline diamond (PCD) has a significant impact on the thermal stability and wear resistance of PDC. Therefore, cobalt removal treatment is required to improve the performance of PDC. The current cobalt removal methods mainly include acid leaching and electrolysis. This study proposes a novel coupling method that combines acid leaching and electrolysis for cobalt removal. Cobalt removal was conducted for 10 h under the conditions of electrolytic voltage of 12 V, direct current power supply current of 0.01 A, and sulfuric acid electrolyte concentration of 9.2 mol/L. The cobalt removal effect was evaluated using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The hardness and elastic modulus of PDC before and after cobalt removal were measured using nanoindentation experiments. The results indicate that the coupled electrolysis process effectively removes the cobalt phase in the PCD layer while retaining the WC phase. The hardness and elastic modulus of PDC decrease after the removal of cobalt binder, and the cobalt removal depth can reach 807 μm.

Constructing coherent/semi-coherent phase boundaries to enhance toughness of superhard cBN-B composite

Harsh synthesized pressure is required in constructing of excellent grain boundary (GB) connection for nano-polycrystalline cubic boron nitride (nPcBN) to yield high hardness and toughness. Therefore, it is urgent to fabricate robust nPcBN composite under relatively mild pressure by developing the hard nonmetal binders to form coherent/semi-coherent phase boundary (cPB, scPB) with cBN. Here, the slight content of nano‑boron was composited with nPcBN to achieve superhard property of 45.2 GPa and high fracture toughness 8.4 MPa‧m0.5 under a relatively mild condition of 5 GPa and 1800 °C. The hardness is comparable with single crystal cBN and the toughness is about three times higher than single crystal cBN. The nano boron connects the nano cBN grains by cPB and scPB, and nano boron filled the triangular space of cBN crystals, which eliminates the defects to prohibit the crack trigger sources and enhances the strength. This work provides a reference and a new strategy on composite engineering in superhard materials with high toughness by relatively mild synthesized pressure.

Explorative prediction of novel superhard carbon allotropes with lager cell: Density functional theory-assisted deep learning

Searching for superhard materials with excellent properties has been a key challenge in materials science over the past decades. In this study, based on high throughput and density functional theory (DFT), we identified 24 new stable carbon allotropes from 50 initially identified candidates through structural optimization by removing repetitive structures and mechanically, molecularly dynamic, and thermally unstable structures. In addition, we built a crystal convolution residual neural network (CCRNN) to predict the elastic properties and mechanical hardness of the carbon allotropes and used chemical formulas as inputs to the model. The model used nearly 9979 target compounds, monomers, and 143 element-based features such as covalent radius, electronegativity, volume, and magnetic moment. To accurately predict carbon allotropes, we added lattice constants (a,b,c) and lattice angles (alpha,beta,gamma) as inputs after the feature descriptors. Random forest (RF) and gradient-boosted decision tree (GBDT) regression algorithms were constructed, and the r of the CCRNN model was 0.978 and 0.955 for the bulk and shear moduli, respectively, and the best model (CCRNN) was chosen to predict the bulk and shear moduli of the stabilized carbon allotropes obtained from high-throughput calculations. Density functional theory validated the machine learning results. This study not only revealed 7 new superhard carbon allotropes, but also proposed a new deep learning model, and these newly discovered superhard carbon allotropes had wide-ranging potential applications in the fields of industry, electronics, aerospace, geology, and biomedicine. Our research has provided an important theoretical and experimental basis for the development of new superhard materials and applications and was significant in advancing the field of materials science and engineering.

Prediction of carbon-based metal-free compounds with antiferromagnetism and superhardness

Magnetic superhard materials are still scarce, although they are very important to magnetic devices in extreme environment. Here, we predict a series of antiferromagnetic carbon-based compounds through stacking diamane and 2D C4N3. The result exhibits that all the ground states of these compounds display antiferromagnetic ordering and superhard nature. The antiferromagnetism originates from the unpaired electrons of the low-coordinated C atoms at the interface. Interestingly, their hardness, magnetic moment, dynamic and mechanical stabilities are independent of the stacking sequence of the two precursors. The Vickers hardness is ∼70 GPa given by Chen model, the magnetic moment is ∼0.44μB. Notably, the magnetic moment is insensitive to the external pressure, whereas the magnetic transition temperature would increase with increasing the external pressure. On the contrary, the electronic property is strongly dependent on the stacking sequence, resulting in energy gaps ranging from 1.00 to 1.30 eV, despite all behaving as semiconductors. This work opens a potential way to design magnetic carbon-based materials with superhard feature.

SPECIFIC ENERGY CAPACITY OF PROCESSING AND ENERGY EFFICIENCY FOR PROCESS OF GRINDING WITH WHEELS FROM SUPERHARD MATERIALS

The analysis of modern research shows that when evaluating the specific energy intensity of the abrasive processing process, one should pay attention not only to the indicators of grinding power and material removal rate, but also to the indicator of the wear of the abrasive tool, which we will show below for the grinding tool made of superhard materials. It is shown that the traditional method of estimating the specific energy capacity based on the ratio of the grinding power to the processing productivity does not provide an adequate solution, since with it the specific heat capacity of processing exceeds the specific heat capacity of melting of the processing material by almost an order of magnitude. Therefore, it is the application of a new approach to the assessment of the specific energy intensity of diamond grinding, taking into account the wear of the working layer of the diamond wheel, and makes it possible to estimate the indicators of the specific energy intensity of grinding and the energy efficiency coefficient. It has been proven that when estimating the specific energy capacity of grinding metal-ceramic composite materials consisting of a low-melting and refractory component, the latent heat capacity of melting of the low-melting component should be taken as the basis. It is shown that the plastic mode of grinding occurs precisely when the specific energy capacity of grinding, taking into account the wear of the wheel, becomes close to the specific heat capacity of melting of a brittle material.

Construction of superhydrophobic tungsten carbide via laser processing and its thermal, chemical and mechanical properties

Designing microscale microstructures on superhard materials and achieving superhydrophobic surfaces through wettability adjustment have promising application prospects. However, current popular methods for preparing superhydrophobic surfaces have not designed and optimized the microstructures, and achieving superhydrophobicity on superhard materials using conventional industrial methods remains a tremendously challenge. Here, we propose a novel multiscale microstructure design on superhard tungsten carbide (WC) alloy material, achieved through laser processing, which exhibits superhydrophobicity after low surface energy modification. To ensure the designed microstructures possesses excellent mechanical strength and wettability, the influence of size parameters on mechanical strength and their relationship with wettability through finite element analysis (Abaqus) and characterization techniques were conducted. Based on the optimized robust multiscale structure, we also investigated the comprehensive properties of the superhydrophobic surface. The thermal, chemical, and mechanical stability of the WC superhydrophobic surface were explored through experiments involving temperature exposure, immersion in acid-base solutions, friction and wear tests. Our findings demonstrate that the superhydrophobic WC surface exhibits excellent temperature resistance over a wide range, maintaining superior water repellency even after prolonged exposure to chemical solutions and mechanical abrasion tests. In addition, the substrate's microstructure and SiO2 nanoparticles successfully replicated on the optical glass surface through molding technology, creating a consistently superhydrophobic glass microstructure. This work provides a new perspective for designing superhard alloy materials with robust microstructures and offers potential for a series of applications, such as mold, semiconductor and solar cell.

Orthorhombic metal carbide-borides MeC2B12 (Me = Mg, Ca, Sr) from first principles: structure, stability and mechanical properties

First principle DFT simulations are employed to study structural and mechanical properties of orthorhombic B12-based metal carbide-borides. The simulations predict the existence of Ca- and Sr- based phases with the structure similar to that of experimentally observed earlier compound MgC2B12. Dynamical stability of both phases is demonstrated, and the phase CaC2B12 is found to be thermodynamically stable. According to simulations, Ca- and Sr- based phases have significantly enhanced mechanical characteristics, which suggest their potential application as superhard materials. Calculated shear and Young’s moduli of these phases are nearly 250 and 540 GPa, respectively, and estimated Vickers hardness is 45–55 GPa.

ИССЛЕДОВАНИЕ ВЛИЯНИЯ СОСТАВА КОМПОЗИТОВ, СОДЕРЖАЩИХ ИМПАКТНЫЕ АЛМАЗЫ, НА ИХ ЭКСПЛУАТАЦИОННЫЕ ХАРАКТЕРИСТИКИ ПРИ ЛЕЗВИЙНОЙ ОБРАБОТКЕ ЦВЕТНЫХ МЕТАЛЛОВ

The paper presents the results of resistance tests of tool composite materials containing nanostructured impact diamonds, in comparison with composites based on synthetic superhard materials, diamond and cubic boron nitride (cBN), and ВК-8 (VK-8) (WC + 8 % Co) hard alloy, during blade processing of workpieces made of brass ЛС-59 (LS -59) (57–60 % Cu) and aluminum alloy AK-7 (Al 92–94 %, Si 6–8 %). Samples of composite materials for wear resistance studies were obtained by thermobaric sintering in a highpressure apparatus. The performance of composites was assessed by the wear of the cutter back surface, as well as by a specially developed method for studying the performance characteristics of composite superhard materials, based on determining their specific productivity. As a result of the tests, it is found that composites based on impact diamonds have the highest resistance when turning non-ferrous metal alloys. In particular, the wear resistance of a composite material containing impact diamonds with the addition of cBN exceeds the wear resistance of cutters made of composite 02 (belbor) by 1.5–3 times, and that of cutters made of hard alloy VK-8 by 8–10 times. Additions of impact diamond to hard alloy in the amount of 6.25 and 12.5 vol.% increase the relative wear resistance of the hard alloy composite compared to the original VK-8 alloy by 10–15 and 20–25 %, respectively.