The use of high-resolution methods of research in the design of the diamond-matrix interface to increase the durability of the diamond tool

The results of studying fundamental and applied problems regarding the formation of boundary layers between diamond and carbide matrix are presented with the goal to develop a highly resistant diamond tool. The new approaches to the synthesis of diamond-carbide materials combining diamond metallization and sintering in a single-stage technology are presented. The developed technology eliminates the re-heating of a metallized coatings which results in their destruction and enhanced graphitization of diamond (these phenomena restrict using metallization procedure to improve diamond retention and synthesis of high-functional composites for diamond tools). The goal of the study is analysis the structural and phase state of the «diamond – carbide matrix» interface in a diamond tool obtained by the new technology and the main factors determining the level of diamond retention in the presence of a metallized coating. Unique opportunities provided by modern high-resolution methods of research were used in the study. The elemental composition and morphological features of the diamond-matrix interface were studied using the methods of scanning electron microscopy, atomic force microscopy, X-ray microanalysis and Raman spectroscopy. Identification of the reaction products, including non-diamond carbon was performed. It is shown that the introduction of the powder-metallizer significantly modified the contact boundaries and provide conditions for improving the chemical and mechanical adhesion of the diamond-matrix system. The formation of the well-developed nano- and sub-microscale roughness of the diamond surface and dense filling of the existing voids with nanoscale layers of metal-infiltrate was revealed. The multilevel organization of highly structured elements of the transition zone with the minimal graphitization ensured the monolithic character and strength of the diamond-matrix bond. Comparative service tests of preproduction and control samples of diamond dressers proved the efficiency of developed hybrid technology (the specific performance of diamond tools increased by 39 – 45%). New fundamental and applied results have been obtained in the field of studying interface zones in crystalline multiphase systems that can be used to regulate adhesion phenomena at the interphase boundaries and develop highly efficient composite materials.

Structural-Phase State of the Interphase Boundary at Thermal Diffusion Metallization of Diamond Grains by Cr and Ti

Structural-phase state of the diamond-metallized coating interphase boundary after thermal diffusion metallization of diamond grains by transition metals Cr, Ti were studied. Metallization were conducted under temperature-time mode corresponding to the sintering of cemented carbide matrices with Cu impregnation. The structural-phase state of the metallized coating and diamond-coating interphase boundary was studied by scanning electron microscopy, X-ray phase analysis and Raman spectroscopy. It was found that a thin continuous metal carbide coating chemically bonded to the diamond and consisting of the corresponding metal, their carbides and small amount of graphite phases is formed during thermal diffusion metallization of diamond by Cr and Ti under the conditions specified in the experiment. It was shown that graphite is formed not by a continuous layer, but in the form of local inclusions. This ensures a strong adhesion of the metallized coating to the diamond through the carbides of the corresponding metals. The results can be useful in the development of compositions and technological methods that provide an increased level of diamond retention in the matrices of tools based on cemented carbide powder mixtures.

Investigation of Filling Phase Percentages on the Performance of WC-Cu Based Hot-Pressing Diamond Bit Matrices

WC-Cu based hot-pressing diamond bit has been widely applied in all-hydraulic geological exploration, as well as deep and ultra-deep well drilling in the oil and gas industry. However, the effect laws and mechanisms of Cu and WC on the metal matrix composite need further study. Therefore, six WC-Cu based metal matrices were designed, and a series of samples with different dimensions were fabricated to conduct some specific physical and mechanical tests, namely, tests of relative density, Rockwell hardness, bending strength, impact toughness and abrasion weight loss. Additionally, the microstructure and diamond retention conditions of the WC-Cu based samples after bending strength test, as well as their wear morphologies after the pin-on-disc wear test, were analyzed by scanning electron microscope. Test results indicate that most of the physical and mechanical properties were improved with the increase of 663-Cu at first, and then monotonously declined. The increase of 663-Cu also shows an important influence on the samples’ microstructure, diamond retention capacity and wear mechanism.

Mechanical Properties of Some Metallic Powder Alloys and Their Contribution to the Performance of Diamond Tools Used for Cutting Granite

This work examined some pre-alloyed cobalt-, iron-, and copper-based powder binder systems—such as those launched commercially under the brand names of Cobalite and Next—in terms of their as-sintered physical-mechanical properties, namely, apparent density, Young´s modulus, yield strength, rupture strength, rupture strain, toughness modulus, and Vickers hardness. These types of sintered products are traditionally used in the fabrication of diamond impregnated tools for cutting granite stones. The following powder binder systems were evaluated: Cobalite HDR pre-alloyed powder, Next 300 pre-alloyed powder, and four other mixtures of these with Cu and Fe powders: Cobalite HDR + 20 wt% Cu; Cobalite HDR + 20 wt% Fe; Next 300 + 20 wt% Cu; Next 300 + 20 wt% Fe. The evaluation methodology aimed to establish criteria for developing new diamond tools and, therefore, it included the measurement of several technological parameters directly related to the cutting performance of the tools (e.g., energy consumption measurements made exclusively in the tool drive motor, forces generated in the tool, tool consumption per unit weight of stone removed by the cutting). The results show the adequacy of the methodology for the optimisation of diamond retention capacity of these types of metal matrices and for improving the working performance of the diamond tools.

Features of the Structural-Phase State of the Diamond-Matrix Boundary Zone in Diamond-Containing Composite Materials

Preliminary metallization of the diamond component, which promotes the formation of chemical bonds on the diamond-matrix contact during subsequent sintering, is used to increase the strength of diamond retention and the durability of diamond-containing metal matrix composites. There are restrictions on carrying out metallization to create diamond composites with a cemented carbide matrix, since reheating the metallized coating at high sintering temperatures of carbide powders leads to its destruction, diamond graphitization and deterioration of the material properties. The structural-phase state in the diamond-matrix contact zone has been studied and the main factors providing the strength of diamond retention in diamond-cemented carbide composites obtained by hybrid technology that excludes the reheating of the metallized coating have been revealed. It was revealed, that the developed hybrid technology combining the thermal diffusion metallization of diamond and sintering according to the self-dosed impregnation scheme in one cycle ensures the production and preservation of the metallized coating by the methods of scanning electron microscopy, X-ray diffraction and X-ray phase analysis, Raman spectroscopy. Comparative tests have been carried out and it is shown that the specific productivity of experimental samples of a diamond tool (ruling pencils) with a metallized diamond component is on 39% higher than same parameter of pencils without metallization.

Correlation of the diamond/matrix interphase zone structure with tool efficiency obtained by technology combining diamonds metallization with matrix sintering

The paper studies structure and phase characteristics of the interphase zone diamond/matrix in dressers made by thermal diffusion metallization of a diamond combined with matrix sintering based on WC–Co and Cu impregnation. The compact arrangement of chromium powder particles around diamond grains and the shielding effect of copper foil create favorable conditions for thermal diffusion metallization of diamond at matrix sintering. A metallized coating chemically bonded with diamond and consisting of chromium carbide and solid solution of cobalt in chromium phases provides a strong diamond retention in the carbide matrix. It was shown that it is formed on the surface of the diamond under the conditions specified in the experiment and the temperature – time sintering mode. The specific productivity of experimental dresser made by hybrid technology at straightening green silicon carbide grinding wheel equaled 51.50 cm3/mg exceeding that of the control dresser made without metallization of diamonds by sintering with copper impregnation by 44.66%.

Numerical Analysis of Diamond Retention in Cobalt and a Copper-Base Alloy/ Analiza Numeryczna Retencji Kryształu Diamentu W Kobalcie I Stopie Miedzi

Why cobalt outperforms other matrix materials in its capacity for diamond retention in cutting tools is considered. To this end diamond loading conditions were modelled to establish the magnitude of stress and strain in the matrix surrounding a working diamond crystal. Only at 315 N did the contact force in Co result in plastic strain of 4-8%, which has a destructive influence on diamond retention. The strain field generated in a poorly performing Cu-40%Co-6%Sn matrix under a load of 190 N closely resembled that generated by 315 N in Co. It is postulated that diamond retention is related to the yield strength and work hardening characteristics of the metallic matrix.

Numerical Modelling of Stress/Strain Field Arising in Diamond-Impregnated Cobalt

The paper presents results of computer simulations of the stress/strain field built up in a cobalt matrix diamond impregnated saw blade segment during its fabrication and after loading the protruding diamond with an external force. The main objective of this work was to create better understanding of the factors affecting retention of diamond particles in a metallic matrix of saw blade segments, which are produced by means of the powder metallurgy technology. The effective use of diamond impregnated tools strongly depends on mechanical and tribological properties of the matrix, which has to hold the diamond grits firmly. The diamond retention capability of the matrix is affected in a complex manner by chemical or mechanical interactions between the diamond crystal and the matrix during the segment manufacture. Due to the difference between the thermal expansion coefficients of the diamond and metallic matrix, a complex stress/strain field is generated in the matrix surrounding each diamond crystal. It is assumed that the matrix potential for diamond retention can be associated with the amount of the elastic and plastic deformation energy and the size of the deformation zone occurring in the matrix around diamonds. The stress and strain fields generated in the matrix were calculated using the Abaqus software. It was found that the stress and strain fields generated during segment fabrication change to a large extent as the diamond crystal emerges from the cobalt matrix to reach its working height of protrusion.