Superhard Composites Research Articles

Prospects for the Use of Fluorinated Nanodiamonds in the Synthesis of Superhard Composites

The paper considers the possibilities of the practical use of nanoscale diamonds with a fluorine-functionalized surface for the synthesis of diamond composites under high pressures and temperatures. Optimal compositions of the initial mixtures and parameters of thermobaric treatment are established. It is shown that composites obtained by sintering homogeneous mixtures of fluorinated microdiamonds and nanodiamonds with the addition of aluminum and cobalt have an increased level of heat resistance and wear resistance which significantly exceeds the level of commercial samples.

Diamond Composites Produced from Fluorinated Mixtures of Micron-Sized and Nanodiamonds by Metal Infiltration.

Improving the operating performance of superhard composites is an important and urgent task, due to a continuing industrial need. In this work, diamond composites with high wear resistance were obtained by sintering fluorinated mixtures of micron-sized diamonds with nanodiamonds at high pressures and temperatures (7–8 GPa, 1550–1700 °C). Aluminum and cobalt powders were added to the diamond mixture to activate the process. The external infiltration of nickel into the diamond layer was carried out additionally during the sintering process, and the effects of nickel infiltration on the structure and properties of composites were studied. The metal melt ensured the mass transfer of carbon within a volume, and the formation of a strong diamond framework. The composition of the additives was selected in such a way that the binding phase became ultimately composed of the intermetallic AlNixCo1−x(x ≤ 1). The Young’s modulus of composites synthesized in this way had a value of 850 GPa, and their wear resistance when turning white granite was more than twice as high as that of premium commercial PDC. The obtained results thus demonstrate that by using nickel to increase melt infiltration into diamond-based composites, the mechanical properties of Al/Co/fluorinated diamond compositions, studied previously, can be further improved.

Synthesis and characterization of mechanical properties of boron–carbon-based superhard composites

In this work, we investigated a modern combined processing technique for the synthesis of lightweight superhard composites based on boron–carbon. We used traditional B4C with precipitates of free graphite and Al powder as initial materials. In the first stage, the composites were fabricated by the self-propagating high-temperature synthesis (SHS) with the subsequent hot pressing of the compound. Further, by the disintegration and attrition milling, the ultrafine-grained powder was obtained. We used HCl and HNO3 acids for the chemical leaching of the powder to remove various impure compounds. At the last stage, a solid composite was obtained by the spark plasma sintering (SPS) method under nitrogen pressure. The main feature of this approach is to implement different synthesis techniques and chemical leaching to eliminate soft phases and to obtain superhard compounds from low-cost materials. The phases were studied by X-ray diffraction and scanning electron microscopy with energy-dispersive spectroscopy. The composites compacted by the SPS method contained superhard compounds such as B13C2, B11.7C3.3, and c-BN. The fabricated composite has an ultrafine-grained microstructure. Using a Berkovich indenter, the following nanohardness results were achieved: B13C2 ~ 43 GPa, c-BN ~ 65 GPa (all in Vickers scale) along with a modulus of elasticity ranging between ~ 400 GPa and ~ 450 GPa.

Bioinspired diamond composites and their dynamic shock performance

The design of high-strength and high-toughness materials that can sustain high shock-wave loadings is crucial for both armor and civil applications. We propose a bioinspired diamond composite that mimics the brick-and-mortar arrangement of nacre from mollusk shells and evaluate its performance for different diamond brick contents using lattice-spring model. In this work, we present a systematic investigation elucidating the effects of volume fraction of diamond brick, on the shock compression response of bioinspired diamond composites. By comparing the nacre-like diamond composite with traditional diamond composite, it was found that the nacre-like diamond composite can reduce damage degree in diamond composite, and improve dynamic strength of diamond composite. More importantly, the damage evolution analysis of the impacted nacre-like diamond composite indicated that there is large-scale crack deflection, which is only cause slight damage to the diamond brick. The obtained numerical results may provide valuable insights into the preparation of superhard composites for numerous engineering applications.

Thermal Stability of TiN Coated Cubic Boron Nitride Powder.

Wear-resistant, super hard ceramic composites based on cubic boron nitride (cBN) are of great interest to industry. However, cBN is metastable under sintering conditions at normal pressure and converts into the soft hexagonal BN (hBN). Therefore, efforts are being made to avoid this process. Besides short sintering times, the use of coated cBN-particles is a way to minimize this process. Therefore, the thermal stability of TiN coated cBN powders in high purity argon and nitrogen atmospheres up to temperatures of 1600 °C was investigated by thermogravimetry, X-ray phase analysis, scanning electron microscopy and Raman spectroscopy. The TiN coating was prepared by the atomic layer deposition (ALD)-method. The investigations showed that the TiN layer reacts in Ar at T ≥ 1200 °C with the cBN and forms a porous TiB2 layer. No reaction takes place in nitrogen up to temperatures of 1600 °C. Nevertheless, the 20 and 50 nm thin coatings also undergo a recrystallization process during heat treatment up to temperatures of 1600 °C.

Superhard Composites with Homogeneous Microstructure and Nanosized Binder, Obtained by Reactive Sintering in the System cBN–Al–TiC

Experimental results obtained on the synthesis, in a cubic apparatus, of composites based on diamond-like boron nitride cBN in the system cBN–Al–TiC are presented. It is shown that for the optimal ratio of the number, size, and relative arrangement of the particles of superhard material and a nanostructured binder high-level properties can be attained without the obligatory intergrowth of particles of superhard crystals cBN–cBN. The composites were sintered at pressure 4.5 GPa and temperature 1450°C. The chosen thermobaric parameters guaranteed complete reactive interaction, homogeneity of the phase composition, and uniformity of the physicomechanical characteristics throughout the entire volume of large-size composites.

Estimation of damage development and the time of failure of cutting inserts made of hard alloys and superhard composites by chemography methods

The results of theoretical and experimental studies aimed at identifying hidden defects in the structure of hard alloys and superhard composites used in the manufacture of cutting tools in order to control and predict gradual and sudden failures of cutting inserts.Damage control of cutting inserts is carried out by microscopic analysis. Deeper damage to the structure can be detected using the method of chemographic imaging. The proposed method is based on obtaining photographs of the oxidative reactions of materials of ultra-low concentrations occurring on the surface of solids under thermobaric loading.Before the moment of a sharp release of the energy of destruction, chemical processes of ultra-low concentrations are activated. Chemography allows to fix the zones where the incipient microcracks and microdefects are ready to actively develop, which can lead to the onset of macrodamage and failure to work.The chemographic image of the plate obtained as a result of the study is compared with the reference sample, as a result of which it is possible to assess the initial defect state of the material and predict the further period of the plate’s operation.The criterion for the existing defects and imperfections in the structure is the change in the blackness index of the chemographic image, the minimum value of which indicates a minimum of structural defects and internal defects in the material under study.The results allow to propose a new method for controlling the surface of cutting plates, which can be easily implemented in any machine shop, which makes its application very promising

Wear Rate of PcBN Cutting Tools Equipped with Nanolayered Protective Coatings

We consider the effect of protective PVD coatings of various chemical compositions on the wear rate of cutting tools equipped with polycrystalline superhard materials (PSHM) based on cubic boron nitride (PcBN). A coating of the nanolayered structure was applied to cutting inserts made of superhard composites of the BH group by a vacuum-arc method using a Bulat-6 setup. Previous tests, carried out under conditions typical for finishing hardened steel, demonstrated high efficiency of coatings containing Ti, Zr, and Cr nitrides. The (TiAlSiY)N/CrN coating is the most effective. The study of the kinetics of tool wear shows that under test conditions, the wear rate of tools along the flank surface of the wear chamfer hz of tools equipped with modified cutting inserts is significantly reduced by an average of 2.3 times. At the same time, no significant differences in the roughness of surfaces processed by tools with uncoated and coated composites were found under test conditions. The results also indicate that the coating does not decrease the wear rate of the tool equipped with PSHM of group BN when processing materials containing a significant amount of the carbide phase in their structure.

Pressureless ultrafast sintering of near-net-shaped superhard isotropic B4C/rGO composites with Ti-Al additives

Superhard composites of B4C reinforced with randomly-oriented reduced graphene oxide (rGO) nanoplatelets are manufactured by a near-net-shape fabrication route based on three successive steps. Firstly, aqueous colloidal processing is used for the environmentally-friendly preparation of a semi-concentrated multi-component slurry (B4C as main component, Ti-Al as sintering additive, and rGO as toughening reinforcement), whose suitability for wet shaping is demonstrated by rheological measurements. Secondly, slip casting is used to produce robust green parts with shapes on demand and microstructures free of macro- and micro-defects. And thirdly, pressureless spark-plasma sintering (PSPS) is used for the ultrafast and energy-efficient densification of the green parts with shape retention. Measurements of shrinkage and hardness, as well as the microstructural observations, are used to identify suitable PSPS temperatures leading to obtaining isotropic B4C/rGO composites that are superhard and almost twice as tough as the monolithic B4C ceramics.

Obtaining superhard composites in the system Cdiam—SiB4—WC under conditions of high pressures and temperatures

Obtaining superhard composites in the system Cdiam—SiB4—WC under conditions of high pressures and temperatures

Diamond-based superhard composites: new synthesis approaches and application prospects

We discuss experimental results on high-pressure and high-temperature (HPHT) synthesis of diamond-like cubic boron nitride (cBN) and diamond with a high concentration of point defects. The presence of active fluids allows obtaining cBN with a carbon content up to 10%. The concentration of boron in the diamond lattice is about 2%, and that of vacancies is two times higher. The concentration and positions of substitution atoms were determined by the Rietveld refinement method. Diamond micropowder reactive sintering with fluid phases was used to synthesize new superhard composites. The microstructure and grain boundaries were investigated by transmission and scanning electron microscopy. Tests of the wear resistance of the new diamond–cBN composites demonstrated that these materials offer good prospects for various applications.

Method of Estimation of Mechanical Properties of the Surface Layer of Cutter Elements Made of Polycrystalline Superhard Composites Based on Cubic Boron Nitride

Abstract—A method of estimating the mechanical properties of the surface layer of working elements made of polycrystalline superhard composites based on cubic boron nitride involving sclerometry at scanning by a diamond indenter has been proposed. Theoretical validation of the method has been provided and thermodynamic parameters of mechanical properties of the surface layer (the value of the activation barrier of initiation of the entropy production process and the capacity for entropy production at a metered impact) have been investigated. Results of the experiments on the performance efficiency of cutter tools made of superhard composites fabricated by lathing of tempered steel are provided and corroborate the theoretical assumptions.

Obtaining superhard composites of the BL group in the cBN(Al)-SiB4-WC system under high pressure and high temperature conditions

Obtaining superhard composites of the BL group in the cBN(Al)-SiB4-WC system under high pressure and high temperature conditions

Сверхтвёрдые композиты на основе алмаза: новые подходы в синтезе и перспективы применения

Сверхтвёрдые композиты на основе алмаза: новые подходы в синтезе и перспективы применения

Метод оценки механических свойств поверхностного слоя режущих элементов из поликристаллических сверхтвердых композитов на основе кубического нитрида бора

Метод оценки механических свойств поверхностного слоя режущих элементов из поликристаллических сверхтвердых композитов на основе кубического нитрида бора

Improvement of performance of finishing of details with a cutting tool

The possibilities of increasing the productivity of finishing blade processing due to the control of cutting modes are analyzed. Prospective approaches to increasing the feed and cutting speed on examples of an oblique cutter, tools equipped with polycrystalline superhard composites based on cubic boron nitride, tools with protective coatings are considered. The use of tools developed taking into account the features of the phenomena occurring in the cutting zone, the use of cutting tools with special protective coatings provides the possibility of performing finishing blades with high productivity.

Nanostructured compacts and composites based on diamond-like boron nitride

Three ways of thermobaric synthesis of nanocompacts and nanocomposites based on diamondlike boron nitride under the pressure of 8 GPa are considered. The structure of specimens is probed via X-ray diffraction and electron microscopy. It is shown that using the titanium and boron nitrides powders accelerates sintering, resulting in high microhardness values and elastic moduli of the obtained superhard composites.

Mechanical properties of surface layer of cutting elements from polycrystalline superhard composites based on cubic boron nitride

Предложено оценивать параметры механических свойств поверхностного слоя рабочих элементов из поликристаллических сверхтвердых композитов на основе кубического нитрида бора режущих инструмент по результатам анализа сканограмм, полученных методом склерометрирования. Представлено теоретическое обоснование метода и рассмотрены термодинамические показатели механических свойств поверхностного слоя – величину активационного барьера запуска процесса производства энтропии и способность к производству энтропии при приложении дозированного воздействия. Приведены результаты экспериментальных исследований работоспособности режущих инструментов из сверхтвердых композитов, полученные при точении закаленных сталей, подтверждающие теоретические выкладки.

Abrasion Resistance of Superhard Composite Materials for High-Performance Mining Tools

Bench tests of the abrasion resistance of hard and superhard inserts — carbide VK8, superhard composites based on cubic boron nitride PCBN, and polycrystalline diamond PDC—for new types of high-performance mining tools were conducted. Comparative tests in terms of fine-grained white granite with tensile strength 15 on M. M. Protod’yakonov’s scale and subsequent evaluation of the dependence of the wear spot area on the volume of removed rock showed that the abrasion resistance of PCBN inserts is 11.5 times greater and PDC inserts 80 times greater compared with VK8 carbide inserts.

Syntheses and studies of superhard composites under high pressure

Materials having Vickers hardness (HV) higher than 40 GPa are considered to be superhard. Superhard material is exclusively covalent and displays superior hardness, incompressibility, and wear resistance, which make this kind of material essential for a wide range of industrial applications, such as turning, cutting, boring, drilling, and grinding. Most of superhard materials are prepared under extreme pressure and temperature conditions, not only for scientific investigations, but also for practical applications. With the development of high pressure science and technology, the field of superhard composites is more active and more efficient, energy saving and environmental protection. Ultrahigh pressure and ultrahigh temperature method plays an important role in the scientific research and industrial production of superhard materials. It provides the driving forces for the light elements forming novel superhard phases and the way of sintering high-density nanosuperhard materials. In this paper, the recent achievements and progress in high-pressure synthesis and research of superhard materials are introduced mainly in the nanopolycrystalline diamond, nanopolycrystalline cubic boron nitride (cBN), ultrahard nanotwinned cubic boron nitride, submicron polycrystalline cubic boron nitride, cBN-Si composites material, cubic-Si3N4-diamond nanocomposites and diamond-cubic boron nitride superhard alloy (composite) material prepared under ultrahigh pressure and high temperature, by using multi-anvil apparatus based on the hinged-type cubic press. These superhard composite materials are successfully synthesized by high temperature and high pressure, and a variety of performance tests show that their hardness values and thermal stability properties exceed those of the traditional superhard materials. At the same time, some new ideas, approaches to the study of superhard composite materials in recent years have been introduced, such as nanostructuring approaches and special treatments of the starting material for high-performance superhard materials, using the formation of alloys or solid solution to fill the performance gap between different materials for enhancing comprehensive performance (i.e., hardness, fracture toughness, and thermal stability), or changing and optimizing the assembly method to improve the uniformity of performance. Finally, the prospect of superhard composite material is also discussed. In the research field of superhard materials, on the one hand, the relationship between macrohardness and microstructure of superhard materials is studied continuously to establish hardness models with atomic parameters, which can be used to guide the design or prediction of novel superhard crystals. On the other hand, highly comprehensive performance and larger size of super-hard composite materials are synthesized for practical application.