Papers by Keyword: Diamond Retention

Abstract: The prospects of using the method of explosive pressing for solving urgent problems of creating high-performance diamond composites for instrumental purposes on binders of powders of fairly cheap materials are substantiated. Purpose of this work is to develop the technology of diamond-abrasive composites synthesis from powders mixtures of natural diamond and widespread low-cost iron-carbon alloys which combines explosive pressing and subsequent short-term high-temperature heating. The processes of varying the compositions of diamond-metal powder mixtures, the parameters of their explosive pressing and the modes of subsequent heat treatment of the resulting compacts are studied. It is shown that the use of explosion energy at the stage of powder briquetting opens up new opportunities for the production of high-performance diamond-containing materials with a matrix of iron-carbon alloy powders. This is due to the specifics of the explosive action which results in the activation of the bonding material which becomes obvious with further high-temperature heating in its intensive hardening and acceleration of diffusion processes. It is revealed that the shock waves create thermobaric conditions that allow for better preservation of the diamond component than with traditional methods of sintering. Samples of abrasive diamond composites with wear resistance corresponding to the level of wear resistance of industrial diamond dressers but with half the consumption of diamond raw materials were obtained.

Abstract: For the enhancement of chemical and mechanical adhesion of natural diamond particles with a hard-alloy matrix during the synthesis of diamond-abrasive composites the hybrid technology which combined in one technological process the thermal diffusion metallization of diamond particles and sintering by the developed scheme of the self-dosed impregnation is proposed. This technology does not include a reheating of the metallized coating that causes its destruction and enhances graphitization of diamond thus limiting the application of metallization method for improvement of diamond retention and creation of high-functional composites for diamond tools. Formation and preservation of adhesion-durable metallized coating is confirmed by experiments simulating the conditions of high temperature interaction of diamond with a carbide-forming metal and a hard-alloy matrix during the sintering of special samples using the regimes of developed technological process. The structural and phase state of the transition zone is studied by scanning electron microscopy, X-ray structure analysis and X-ray phase analysis of the partition surfaces of the contact zone between the diamond and the matrix obtained by tensile testing of special samples. Comparative service properties tests of prototype and control samples of diamond dressers confirmed efficiency of the developed hybrid technology for the creation of diamond tools.

Abstract: 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.

Abstract: The conducted study belongs to a field of fundamental and application-oriented issues of interphase interaction and formation of interfacial layers between a filler and matrix during the synthesis of composite systems. The factors determining the strength of the diamonds retention in a hard-alloy matrix of abrasive composites obtained by the hybrid synthesis technology with thermal diffusion metallization of diamond particles and sintering by a scheme of the self-metering impregnation were studied. Chemical composition, morphology and distribution of the reaction products, the nature of the resulting carbon phases in the contact zone between the diamond and matrix were investigated using scanning electron microscopy, X-ray phase analysis, Raman spectroscopy and atomic force microscopy. It was found that the increase of physical and chemical adhesion of diamond with the matrix during the synthesis of composites by the developed technology occurs due to the formation of high nano- and submicronic roughness of the diamond surface, formation of island-type metallized coating, dense filling of gaps by nanoscale layers of metal-infiltrate. Free carbon (graphite) was found in small quantities in the form of micron dimension separate inclusions. The revealed multilevel hierarchy of the high-structured morphological forms of the elements of the transitional layers has provided the solidity and strength of the joint between diamond and matrix.

Abstract: The paper is concerned with the modelling of diamond retention efficiency of three different matrix materials: cobalt (EF), cobalt (SMS) and carbonyl iron powders. After the consolidation stage, the specimens were tested for tensile properties. The mechanical fields around a diamond particle were determined using computer simulations. The simulations were performed for a protruding diamond particle after hot pressing and after loading with an external force. The diamond retention efficiency of the matrix is affected by the interactions between the diamond crystal and the matrix during hot pressing. It is assumed that the matrix potential for diamond retention is associated with the amount of elastic and plastic deformation energies. The mechanical state generated in the matrix was calculated using Abaqus software.

Abstract: An investigation was undertaken to elucidate the mechanisms for the fracture failure of brazed diamonds in wire sawing. Diamonds were brazed by high-frequency induction in vacuum. The changes of compressive strength and the appearances of the diamonds at different brazing temperatures were obtained. The morphologies of the diamonds after sawing were also observed. Together with the stress analysis of a brazed grit, it is found that the fracture failure of brazed grit is the result of the brittle fracture happening on the root section of the grit, the interface between the grit and the brazing alloy. The degradation of mechanical properties of grits in brazing is a key factor to the reduction of their resistance to fracture. Lower machining forces as well as grit exposure are in favor of preventing grits from fracture.