Polycrystalline Superhard Research Articles

On the mechanism of rock fracture with tools made of hard alloys and polycrystalline superhard materials

When studying the process of rock fracture with tools equipped with polycrystalline superhard materials (PSHM) and hard alloys, the main regularities of the fracture mechanism, despite the significant differences in physical and mechanical properties of the used tool materials, are assumed to be identical. This approach not only reduces the efficiency of using the created rock-destroying tools, but also limits the scope of application of polycrystalline superhard materials. Experimental studies using various methods of obtaining information shown significant differences in the mechanism of rock fracture by hard alloys and polycrystalline superhard materials. The study of the zone of the pre-destroyed surface showed that when cutting rocks with PSTM, the process of destruction is carried out not only by the entire polycrystalline plate, but also by ridged diamond formed on the cutting edge and rear surface of the tool. At the same time ridged diamonds, when embedded in the rock, create high contact stresses and an additional network of microcracks interacting with microcracks formed due to the embedding of the entire cutting edge of the plate. The impact of two independent indenters simultaneously increases the zone of the pre-destruction layer in the rock mass, which leads to a more significant decrease in its strength and, as a consequence, to the intensification of the process of rock destruction by the PSTM tool. In case of wrong choice of PSTM application area and operation modes, errors in tool design and insufficient cooling, ridges are not formed on the cutting edge and back surface of the polycrystal. As a result, the polycrystalline insert works as a carbide insert and the efficiency of the PSHM tool is sharply reduced. The use of knowledge obtained as a result of the conducted research makes it possible to create tools equipped with diamond-hard-alloyed inserts, the wear resistance of which is dozens of times higher than that of similar tools made of hard alloy. For example, effective tools equipped with diamond-hard-alloyed inserts have been created and widely introduced into practice for rotary drilling of boreholes, degassing wells, anchoring of mine workings, saw stone cutting, drilling of abrasive permafrost soils and others. Keywords: polycrystalline diamonds cutters (PDC), hard alloys, pre-destruction zone, rock breaking tools, rock destruction.

SIMULATION OF THE STATE OF THE CHIP FORMATION ZONE DURING FACE MILLING OF HARDENED STEEL

The article considers the results of modeling the stress-strain and thermal state of the cutting zone during face milling of hardened steel with a tool equipped with polycrystalline superhard composite based on cubic boron nitride. The influence of strengthening the surface layer of the processed material, characteristic for different passes of different tools, on the cutting forces, shrinkage of chips, the length of contact of chips with the front surface of the tool is shown. The connection of non-stationary nature of machining with incisions of each of the tool blades and exit from the cutting zone with the presence of periods of increase in cutting temperature and cooling of the cutting tool has been studied.

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.

THE PECULIARITIES OF SETTING THE GRINDING COEFFICIENT IN THE PROCESSING OF POLYCRYSTALLINE SUPERHARD MATERIALS

The questions related to the peculiarities of determining such a physical characteristic of the process of grinding polycrystalline superhard materials by diamond circles on metal and organic bonds as a coefficient of grinding are considered. It is the ratio of the tangential and normal components of the cutting force when grinding. It is proposed to determine it using the effective component of the tangential component of the cutting force. Its establishment is based on the use of the phenomenon of adaptation of the grinding process in general and its individual component, the periodicity of change in time of physical and technological indicators of processing in particular. The physical nature of the occurrence of the periodicity with respect to the conditions of the controlled grinding process according to the elastic scheme and to the conditions of the process of grinding polycrystalline superhard materials diamond circles on organic bonds in the self-sharpening mode is disclosed. It was established that when using the first process as a factor of forced influence on the state of the cutting surface of a circle it is necessary to choose the magnitude of intensity of electrophysical solution of the metal ligament of the diamond circle, and in the second transverse supply to the depth of processing. Recommendations regarding the choice of factors of forced influence are given. It is shown, that the peculiarity of the elastic treatment scheme is that the normal component of the cutting force is constant in time. Therefore, the change (increase or decrease) of the effective component of the tangential component of the grinding force leads to similar changes in the grinding coefficient and can clearly judge the effectiveness of the method or conditions of grinding that explores. In contrast to the elastic circuit grinding when working on a rigid scheme, both components (tangential and normal) grinding force, which are used to define the grinding coefficient, depend on the processing conditions. This fact should be considered when analyzing the obtained experimental data. In the future, research results will help to improve the grinding processes of polycrystalline superhard materials.

THEORETICAL REASONING FOR EFFICIENT USE OF MICRO POWDERS IN DIAMOND WHEELS ON METALLIC BONDS

The article presents theoretical researches of improving the manufacturing process and the subsequent using of grinding wheels from diamond micro powders of diamond on current-carrying bonds, which allow to reduce the specific consumption of synthetic diamonds in the finishing operations of processing polycrystalline superhard materials It is proposed to use diamond grains with a metal coating in an abrasive tool. 3D analysis of the stress-strain state “diamond grain-coating-bond” system showed ways to reduce the probability of destruction of diamond grains during sintering of the diamond-carrying layer by changing the thickness of the coating, the elastic modulus of its material and other parameters. The calculated low values of the concentration of coated diamond grains provide a significant reduction in their specific consumption in the processing of polycrystalline superhard materials.

Influence of diamond component based on wurtzite boron nitride on wear resistance of cutting tool

The article is devoted to the study of the influence of the diamond component in a composite superhard material based on wurtzite boron nitride on the stability of the tool during turning of hardened steels in the mode of smooth turning and when processing intermittent surfaces. The aim of the work is to study the influence of the content of the diamond component in the composite superhard material based on wurtzite boron nitride on the stability of the tool. Based on the analysis of the main patterns of changes in the coefficient of friction depending on various factors, the evaluation of composites containing diamonds of different dispersion in comparison with other materials of this class. The results of the study of the technical level of composite polycrystalline superhard materials based on wurtzite boron nitride of different composition and determination of the efficiency of their use as a cutting tool in the machining of hardened steels are presented. The intensity of wear of composites in the cutting tool during processing of hardened steels is experimentally determined. It is established that the presence of a diamond component in the composite significantly affects the stability of the tool in the conditions of smooth turning due to heat dissipation in contact with the processed material. In the processing of hardened steels with the presence of shock loads, the phase state of the matrix component of the composite plays a decisive role. The obtained research results make it possible to determine the optimal composition and conditions for obtaining a composite material of the system “boron nitride – diamond”, which provides the most effective application of the cutting tool in practice.

SPECIFICITY OF USING DIAMOND MICROPOWDERS IN WHEELS ON METALLIC BONDS

Some issues related to the possibility of increasing the efficiency of shaping blade tools from polycrystalline superhard materials by diamond grinding are considered. It has been established that one of the ways to increase the efficiency of using diamond micropowder grains in circles is to apply thick metal coatings on them. The use of embossed metal coatings on diamond grains can significantly extend their cutting resource. This is explained on the one hand by a stronger adhesion of the coating material to the diamond surface compared to the components of the binder, and on the other hand, a significant increase in the contact surface of the coated grain with the binder of the circle. It was established that the strength of metal and ceramic ligaments should be consistent with the strength of diamond grains sintered with it, and the concentration and graininess of the latter have a significant impact on the integrity of the grains in the sintered layer.

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.

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

Drilling of Composites Using Tools of Polycrystalline Superhard Materials

The advantages of using tools of polycrystalline superhard materials for drilling workpieces of fiber reinforced composites are shown. The results of a comparative quality assessment of holes produced by high-speed steel drill bits and polycrystalline diamond inserted drill bits are discussed. The polycrystalline diamond inserted drill bits have been found to provide high-quality drilling of fiber reinforced composite materials.

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.

Special features of the applications of cutting tools from polycrystalline cubic boron nitride with protective coatings

The results of the investigations on the efficiency of cutting tools from polycrystalline superhard materials based on cubic boron nitride with a protective coating. A hypothesis is proposed for the increase of the cutting tool life in turning hardened steel due to a decrease of the temperature in the cutting zone and a complex of physico-mechanical properties of the protective coating required for this is analyzed. A protective coating of boron nitride is considered in the amorphous state that plays a role of a solid lubricant in the zone of the tool contact with cutting chips, decreases the temperature in the contact zone through the reduction of the contact length and cutting force, ensures an increase of the tool life and reliability, especially at the stage of the run-in.

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.

Cutting of polycrystalline superhard materials by jet methods

The authors study the intensity of cutting workpieces of hardmetals, polycrystalline cBN-based material and polycrystalline diamond-on-hardmetal compacts in the following operations: waterjet cutting, laser cutting, liquid-cooled laser cutting, and laser–jet cutting. Special features of cutting two-layered composites that comprise a polycrystalline diamond layer on a hardmetal substrate are analyzed. The paper demonstrates the efficiency of the hybrid machining process that combines the laser–jet and waterjet technologies and provides an effective cutting of workpieces to a required profile.

Special features of the compaction and phase transformations of wurtzitic boron nitride nanopowders under the action of high static pressures and temperatures

The experimental results of special features of the compaction and attendant phase transformations of compacts formed in sintering wurtzitic boron nitride nanopowders at high static pressures (p = 7.7 GPa) and temperatures (T = 1100–1800°C) have been considered. The principal possibility to produce polycrystalline superhard materials with nanocrystalline granular structures based on wurtzitic boron nitride has been established. The compaction of nanodispersed wurtzitic boron nitride at high barothermal conditions has been found to correspond to common regularities of the compaction of dispersed powder systems with regard to the effect of the phase and structural transformations.

AlN-(TiCr)B2 ion-plasma coating for cutting tools of cBN-based polycrystalline superhard material

The microstructure and oxidation kinetics of the surface layers of AlN-(TiCr)B2 coating produced by magnetron RF sputtering have been studied in the course of the coating formation and use in tools of cBN-based polycrystalline superhard materials in machining ShKh 15 hardened steel. The coating is formed with the liquid phase present. After cutting the formation of two-layer tribofilm with a nanosized external layer has been revealed on the surface of the cutting insert. The tribofilm phase composition has been defined by a layer-by-layer Auger analysis. The film external nanosized layer is a glassy phase as solid solutions of Fe2O3-Al2O3 oxides that acts as a solid lubricant. As the cutting speed increases, the wear rate of a tool with a coating has been found to decrease as compared with tools without a coating.

Simulation of Grinding Process of Polycrystalline Superhard Materials

The results of investigation in order to increase the efficiency of using diamond-abrasive and edge tool made of superhard materials (SHM) on the basis of 3D methodology of complex research of the interrelated processes of their manufacturing and operation are presented. Creation of 3D simulation methodology of processes of sintering of abrasive-diamond tools and processes of grinding of edge SHM tools with their application allows us to increase considerably the reliability of obtained results, to reduce the extent of experimental studies for determination of optimum conditions for grinding and to develop new technologies, tools and equipment. The scientific hypothesis about the expediency of using diamond powders with thick metal coatings in diamond-abrasive tools on metal bonds are proposed and proved on the basis of theoretical research. The research results are implemented as a number of grinding techniques with controllable cutting relief of the wheels and devices which realize them. Using the results of the research makes it possible to increase the reliability of the edged tool made of SHM as far back as at the stage of its sharpening.

Wear and life of tools with inserts from cBN-based polycrystalline Superhard materials in the finish turning of hardened steels at heavy feeds

The results have been considered of experimental studies of the wear regularities of tools with polycrystalline superhard materials based on cubic boron nitride (PCBN) in high-performance finishing of hardened steel with oblique cutters. The effect of machining conditions on the life of such tools has been analyzed.

Hardness of superhard polycrystalline materials and its temperature dependence

Data on the hardness and fracture toughness of diamond and cubic boron nitride-based polycrystalline superhard materials and the temperature dependence of these materials’ hardness have been considered. It has been found that the temperature dependence of hardness of polycrystals, based on diamond and boron nitride, produced from powders having various dispersions, shows a decrease in hardness of all the materials and difference in the materials thermostability.

Hard “skiving” turning

The results of the comprehensive studies of a highly efficient method of finishing, the so-called hard “skiving” turning, are discussed. Special features of the oblique cutting with a tool equipped with cBN-based polycrystalline superhard materials are shown, the regularities of the surface roughness formation and surface layer hardening in machining are considered.