Diamond Segments Research Articles

Interface characteristics and performance of pre-brazed diamond grains with Ni–Cr composite alloy

This study aims to improve the bonding strength of diamond abrasive grains to the matrix in sintering diamond segments. To achieve this goal, a new method of surface metallization of diamonds was developed by brazing using Ni–Cr composite alloy. The diamonds metallized by brazing are called pre-brazed diamonds. Brazing equipment was a vacuum resistance furnace. Diamond segments consisting of the pre-brazed diamonds and the metal matrix were fabricated. The static compressive strength and impact toughness of the pre-brazed diamonds were measured. The bending strength of the segments was also measured. The interfacial microstructure of the pre-brazed diamonds and the segment fracture surface were characterized. The compressive strength and impact toughness of the pre-brazed diamonds peaked when 30wt.% Ni–Cr alloy was used in the Ni–Cr composite alloy. Elemental distribution showed that Cr mainly concentrated at the joining interface of the pre-brazed diamonds. An interfacial resultant composed of Cr3C2 and Cr7C3 was formed at the joining interface of the pre-brazed diamonds. A strong bond was formed at the joining interface between the pre-brazed diamonds and the metal matrix when sintering diamond segments.

Unique large diamonds in a ureilite from Almahata Sitta 2008 TC3 asteroid

The Almahata Sitta MS-170 ureilite (a piece of a breccia originating from the asteroid, 2008 TC3) consists mainly of olivine, with many diamond and graphite grains existing between the olivine grains. The occurrences of the diamonds are unique; i.e., (i) some diamonds exhibit sub-euhedral habits and (ii) some diamonds have large grain-size (up to about 40μm). Several diamonds are segmented into many fragments by fractures. Individual fragments have similar crystallographic orientation, which implies that the adjacent diamond segments were originally a single crystal. Large diamond assemblages occur besides such individual diamond grains. In one of the largest assemblages (almost about 100μm in size) has also the same crystallographic orientation. They can be regarded as the pieces of a previously unique single diamond, which provides evidence for large single-crystals diamond in meteorites. Almahata Sitta MS-170 is a meteorite fragment from the 2008 TC3 asteroid that underwent less shock than other ureilitic meteorites. It is unlikely that such large diamonds were formed from graphite through a shock-induced phase transformation during planetesimal collision, despite this idea being now widely accepted as the diamond formation mechanism of ureilites. Fine-scale heterogeneous distribution of impurities (hydrogen, nitrogen, and oxygen) exists in single crystal diamonds, indicative of sluggish growth. This distribution is reminiscent of sector zoning growth. Its grain size, the shock features of MS-170, and the C- and N-isotopic composition signatures allow us to revive classical and but not widely accepted models for diamond formation in ureilites; i.e., a diamond formed from partially melted magma or a C–O–H fluid in the deep interior of the ureilite parent-body or, alternatively, through a chemical vapor deposition (CVD) process in the solar nebula. Considering present mineralogical and isotopic features, the former scenario is more favorable.

Dependence of mechanical properties of diamond segments on their composition

The work is devoted to studying the mechanical characteristics of diamond-drilling-tool matrix. The infiltration method at temperature of 1100–1150 °C for 15 min in hydrogen medium was used for production of model diamond-containing and diamond-free samples of 24×7×8 mm matrices of two types, which differ in the contents of nickel and cast tungsten carbide, namely WС–Co–Cu ( 1 ) and WС–Со–Cu–Ni + cast tungsten carbide ( 2 ). Dia- monds A8K160 (500/400 μm), AC50 (500/400 μm) and SDB1125 (30/40 mesh, i. e. 600/425 μm) were used as filling materials - their density in matrix was 9 vol.%. Bending strength, hardness, density, porosity, and abrasive resistance of drilling tool matrix samples have been measured. It is found that WС–Со–Cu–Ni matrix samples have higher hardness and abrasive resistance as compared with WС–Со–Cu, these characteristics are explained by existence of nickel and cast tungsten carbide solids in them. Introduction of diamonds in the matrices results in sugnificant increase in their hardness (by 8–10 HRC units), distorting the hardness measured data of matrices in diamond layer of crown bits.

Composition dependence of mechanical properties of diamond segments

This research is devoted to studying the mechanical characteristics of diamond-drilling-tool matrix. The infiltration method at a temperature of 1100–1150°C for 15 min in hydrogen medium was used for making model diamond-containing and diamond-free samples of 24 × 7 × 8 mm matrices of two types differing in content of nickel and fused tungsten carbide, namely WC-Co-Cu (1) and WC-Co-Cu-Ni + cast tungsten carbide (2). A8K160 (500/400 μm), AC50 (500/400 μm), and SDB1125 (30/40 mesh, i.e., 600/425 μm) diamonds were used as diamond-filling materials with a concentration of 9 vol % in the matrix. The bending strength, hardness, density, porosity, and abrasive resistance of drilling tool matrix samples are measured. It is found that WC-Co-Cu-Ni matrix samples have higher hardness and abrasive resistance when compared with WC-Co-Cu, which is explained by the occurrence of nickel and solid particles of tungsten carbide solids in them. The introduction of diamonds in the matrices results in a substantial increase in their hardness (by 8–10 HRC units), which distorts the hardness measured data of matrices in the diamond layer of drill crowns.

Microstructure and mechanical properties of pre-brazed diamond abrasive grains using Cu–Sn–Ti alloy

A new method of surface metallization of diamond abrasive grains was developed using Cu–Sn–Ti brazing alloy. The diamond grains metalized by brazing are called pre-brazed diamond grains. Brazing equipment was vacuum resistance furnace and high-frequency induction furnace separately. Diamond segments consisting of the pre-brazed diamonds and metal matrix were sintered. The static compressive strength of the diamonds and the bending strength of the segments were measured. The interfacial microstructures of the diamonds and the segment fracture surface were characterized. The surface micrograph of the diamonds brazing in vacuum resistance furnace was better. When the mean weight gain rate of the diamonds was 6.4%, the mean strength value of the diamonds was 2533.4MPa. Elemental distribution showed that Ti mainly concentrated at the joining interface of diamond/Cu–Sn–Ti alloy. The interfacial resultant containing TiC was formed at diamond/Cu–Sn–Ti alloy interface. Good interfacial bonding strength was formed at the joining interface of pre-brazed diamonds/metal matrix.

Structure and Mechanical Properties of Impregnated Diamond Cutting Tools Using Cu-Based Metal Matrix

Cu-based metal matrix, Ti coated and uncoated diamond composite were prepared by hot-press sintering in vacuum. The effects of the mixing time and the sintering temperature on the relative density, hardness and transverse rupture strength (TRS) of the matrix were studied. Structures of specimens sintered at different temperatures were studied by XRD. The TRS and wear resistant of coated and uncoated diamond segment were compared. The results show that the optimum mixing time is 20 hours; with the increase of sintering temperature, the relative density, hardness and TRS of the matrix firstly increase and then decrease; the TRS of diamond segment is lower than the matrix sintered at the same temperature and TRS of Ti coated diamond segment increased by 6.18% as compared with uncoated diamond segment; moreover the wear resistance of Ti coated diamond segment is better than that of uncoated diamond segment.

Study on Flaw Detection in Welding Zone of Diamond Saw Blade

In this paper X-ray and penetrant inspection were applied to detect flaws in welding zone between diamond segment and matrix in order to detect position and form of the flaw. The result can be used to assess weld quality and performance of diamond saw blade. The result shows that main flaws on welding zone are crack, incomplete fusion, lack of fusion, pore. These flaws can affect the life and machining precision of the diamond saw blade. We can improve the welding process to ensure welding quality and reliability of saw blade by detected flaws.

Particle Size Distribution and Shape Characterization of the Chips Produced During Granite Machining in Relation to Process Forces and Specific Energy

The objective of the present work was to characterize the particle size/size distribution and shape of the chips produced during granite machining in relation to process forces and specific energy. To achieve this goal, two different series of circular sawing experiments were performed on an instrumented full-scale rig. The first series of sawing tests was carried out with a newly dressed blade, while the second series of tests were carried out at a relatively worn state. For each case, cutting forces and specific energy values were determined. By using a computer image-processing system, size and shape descriptors of the collected chips from the cutting debris of both series of tests were quantitatively evaluated. The results of the analyses showed that the size/size distributions of the produced chips were greatly influenced by the wear state of the diamond segments. Size/size distribution characteristics of the chips were also found to correlate with the force ratio and specific energy, indicating that particle size analysis of the cutting debris could be used as an efficient guide to sawing efficiency in industrial applications. Despite to diversity in their size/size distribution characteristics, the chips produced in both series of sawing tests showed quite similar shape characteristics.

Effect of cooling liquids on cutting process using diamond segmented disc of natural stones

In this study, various cooling liquids considered as alternatives to water were investigated for cutting performance of diamond sawing disc utilized in cutting process of natural stones. In experiments, four various cooling liquids such as water, Ace-Cool, boron oil and liquid soap and two different natural stones (Blue Pearl and Nero Zimbabwe) were used. Down-cutting mode was selected for cutting experiments. In experiments, power consumption, cutting forces, specific energy, diamond segment wear and diamond crystal failures were determined. Power consumption of diamond sawing disc was measured through an energy analyzer and cutting forces through a three-directional dynamometer (ESIT). Specific energy values were calculated through an analytical method on the basis of the resulting power consumption and cutting forces. Besides, diamond segment wear was measured through a laser device (KEYENCE) and diamond crystal failure in cutting process was analyzed through scanning electron microscopy on the basis of cooling liquids. Results of the study show that various cooling liquids proposed as alternatives to water increase significantly cutting performance of the diamond sawing disc. While maximum cutting performance was achieved with a mixture of water and boron oil, minimum performance was achieved through use of water.

Electrical Discharge Truing of a Vitrified Bonded Superabrasive Wheel with Electrical Conductivity

With its high grit retention and easiness to true and dress, the vitrified bond is widely used as a bond material for cBN and diamond grinding wheels. By giving electrical conductivity to the vitrified bond, application of electrical discharge trueing/dressing and detection of a workpiece position by electrical contact sensing will become possible. And moreover, application of the vitrified bonded wheels to various types of electro-assisted grinding processes (electrochemical or electro discharge assisted methods) is expected. In this study, vitrified bonded diamond segments with electrical conductivity were manufactured experimentally by mixing the fine copper powders in the vitrified bond matrix. As a result of investigation into the electro discharge trueing performance in the die sinking and wire electro discharge machining, it was found that a vitrified bonded wheel could be formed by electro discharge machining only because the bond was electrically conductive. In addition, the electro discharge complex grinding utilizing electric discharge machining was applied to the PCD cutting tool materials using the electrically conductive vitrified bonded wheel, and confirmed that the grinding could be continued for a long time maintaining a stable grinding force.

Prediction of sawing performance based on index properties of rocks

Performance analysis of all systems used in industrial production is very important subject in terms of capturing the low production cost. This subject is also important for choosing production methods in natural stone processing. Circular sawing is a commonly used method in natural stone processing. The preliminary prediction of circular sawing performance is very useful for stone producers. In this study, the prediction of sawing performance from some index properties of stones was conducted. The unit wear on diamond segments was evaluated as performance criteria. The statistical analysis was carried out, and this performance parameter was predicted from some index properties including cone indenter hardness, Shore hardness, Bohme surface abrasion, and brittleness. The most suitable prediction equation derived from regression analysis was selected. It was determined that this equation was statistically reliable for prediction of unit wear for natural stone processing.

Optimization of limestone sawing using circular saws with reference to unit wear and energy

Natural stone processing operations use different methods and machines; however, the circular sawing machines are widely used in natural stone processing since they can be used flexibly. The wear on the diamond segments on the sawblade and energy consumption are the important parameters for these machines. Unit wear and unit energy should be minimized and the sawing rate should be maximized for optimum sawing condition. In this study sawing tests were performed on limestone samples using a fully automatic circular sawing machine. The tests were conducted at different peripheral speeds and advance rates. For each sawing test, the segment wear and consumed energy were measured. The statistical software, Design Expert 7.0 was used to analyze the test data. The new sawability charts for wear and energy were developed. The unique aspect of this study is to determine the optimum circular sawing performance with the special software and this technique also provides the prediction of unit wear and unit energy for selected sawing condition.

Characterizations and mechanical properties of impregnated diamond segment using Cu-Fe-Co metal matrix

Diamond impregnated Cu-Fe-Co based saw-blade segments are directly processed by vacuum and pressure-assisted sintering at different temperature, with the purpose of reducing the cobalt content in diamond tools. Copper and iron are used as the bonding elements and cobalt-chrome pre-alloyed powder is used as the hardening phase. Effects of sintering temperature on microstructures and mechanical properties of the sintered matrix and diamond graphitization were investigated by X-ray diffraction analysis, electron probe micro-analyzer, universal testing machine, digital Rockwell hardness tester and Raman scattering analyzer. Results showed that microstructures of the sintered matrix were refined and porosities in the sintered matrix were closed to a more spherical-like shape with the increase of the sintering temperature. Densification, hardness and tensile strength of the matrix sintered at 820 °C were 12.75%, 2.72% and 156.38% higher than that of the matrix sintered at 740 °C, respectively. Diamond graphitization was not occurred at 820 °C. The hardness and the tensile strength rose 32.8% and 13.5%, respectively, after 7.5 h ageing treatment. The matrix densification ascent and the dispersed distribution of Co-Cr pre-alloyed powders contributed a hardness improvement and a tensile strength improvement to the Cu-Fe based matrix.

Stress evolution and cracking of crystalline diamond thin films on ductile titanium substrate: Analysis by micro-Raman spectroscopy and analytical modelling

In this study, the cracking of a brittle diamond coating on a titanium substrate under tensile straining was investigated by micro-Raman spectroscopy and analytical modelling. The in-situ micro-Raman investigations showed that the fracture strength of the coating is ∼1.5 GPa, and it contains an initial compressive residual stress of ∼−5.4 GPa which can be reduced by the application of uniaxial tensile strain. At higher strains, the compressive stress was transformed into the tensile regime and cracks appeared in the coating, followed by a reduction in crack spacing and finally delamination. The stress measurements across different cracked coating segments, using Raman spectroscopy, indicated tensile stresses at the middle and compression near the edges of the segment under tensile load. Coating fragmentation leads to a relaxation of the stress within the cracked coating segment. Further cracking of the smaller segments requires larger strains. Here, the classical shear lag model was extended to derive the stress distribution in the coating bonded to the substrate, considering both residual stress and cracking using a fracture criterion. The effect of substrate plasticity on the evolution of residual stress and on the cracking behaviour of the coating is also introduced. A good agreement is found between the modelling approach and the measured failure behaviour as well as the stress distributions in the fractured diamond segments.

Effects on the Bending Strength of Metal-Bonded Diamond Segments in DEM Simulation

An attempt was taken to simulate the bending strength of diamond impregnated segments in three point bending tests by using a discrete element method (DEM). The influences of main bond matrix components (Fe and Cu), the porosity in the matrix, the coefficient of friction among the matrix particles, and the connection strength between abrasive particles and matrix particles on the bending strength were investigated through simulation. It is found that the bending strength increases with the proportion of Fe but decreases with the increase of porosity. An increase in both the friction coefficient of the matrix particles and the bonding strength between the diamond grains and metal matrix particles can also lead to the increase of bending strength.

Efficient drilling of holes in Al 2O 3 armor ceramic using impregnated diamond bits

This study aims at achieving a high efficient mode of hole-drilling in Al 2O 3 armor ceramic by using impregnated diamond bits. First, the most suitable diamond segment for the armor ceramic is selected by using higher quality diamonds and varying the composition of the metal matrix, as well as combining to the drilling test and SEM examination. Bit structure parameters such as grain size, diamond concentration, number of slots and wall thickness are optimized then by an orthogonal test. Experiments for analyzing the influence of the axial force and spindle speed to the efficiency are also carried out. Then hole quality is discussed. Finally, the ground surface integrity of Al 2O 3 armor ceramic is analyzed under SEM examination. The results show: (1) the bit with diamond type of SMD40 and metal matrix of Cu50Co25Sn18Ti7 (wt%) presents the best self-dressing capability among the four kind of different matrix bits; (2) the bit with wall thickness of 2.5 mm, grain size of 35/40 US mesh, diamond concentration of 100% and number of slots of 2 achieves a higher efficient mode; (3) the increased axial force and spindle speed could increase the drilling efficiency but overlarge axial force and too high spindle speed also lower the efficiency; (4) hole quality can be improved by using an prepress exerted device; (5) the ground surface of Al 2O 3 armor ceramic is composed of fractured area and ductile streak area which indicate that the material removal mode is contributed by both brittle fracture and ductile cutting, and the brittle fracture removal is dominant.

Surface Modification of Press Dies Used in a Powder Metallurgical Production Process

AbstractCold compaction in a press die and subsequent sintering of diamond particles, homogeneously distributed in a metallic powder as matrix, is one of the most economic ways for the production of diamond composites, used widely for cutting very hard materials like stone and glass. Owing to the very high hardness of diamonds, the wear of the press die is considerably high and because of a short life time, press tools must be substituted regularly. Recently, through plasma nitriding process and deposition of thin solid films, the wear resistance of the press dies has been significantly increased. This work aims at the investigation of the influence of roughness, friction coefficient, and hardness of the inner surface of various dies, which have been modified in different ways, on the physical properties of the compacted diamond segments. It was evidenced that improving the mechanical and tribological properties of the die surface leads to an increase of the hardness and density of the diamond composites produced.

Improvement of press dies used for the production of diamond composites by means of DUPLEX-PVD-coatings

In the machining of hard materials such as glass or stone, cemented carbides have been recently replaced by diamond tools, consisting of a metallic carrier, on to which diamond segments are brazed. One of the most economic ways for the production of diamond segments is the cold compaction of the mixture of a metallic powder and diamond particles. Due to a highly abrasive sliding contact between diamond particles and the die walls, the wear rate of the press dies is very high. As a result of a low lifetime of the press dies, they must be replaced in short time periods. To avoid the costly and time-consuming substitution of the press dies, in this work PVD-coatings were deposited on the inner surface of the pre-plasma nitrided press dies (DUPLEX treatment). Thereby, various high and low alloy tool steels were treated by means of plasma nitriding process. Subsequently, a nanocomposite TiAlN coating (nc-TiAlN) was deposited by means of a high ionization magnetron sputtering device on nitrided and non-nitrided steel substrates. The mechanical and tribological properties of these coating systems were studied by means of several standard tests such as nanoindentation, ball-on-disc and scratch test. The most wear resistant coating system was chosen to employ on the inner surface of the press dies. The wear resistance of the press dies developed in this study was tested under real loading condition during compaction of the mixture of diamond particles and cobalt powder. It was revealed that employing plasma nitrided tool, steels coated with nanocomposite TiAlN decreases the wear rate of the press dies up to 76%.

The effects of circular sawblade diamond segment characteristics on marble processing performance

Utilizing a fully instrumented block-cutter, an experimental study was carried out to investigate the effects of diamond/metal matrix properties on the sawing performance of segmented circular sawblades. Six commercially available sawblades differing in segment compositions were used in the sawing experiments of Afyon Tiger Skin Marble. Bond compositions of the tested sawblades were determined by carrying out energy dispersive X-ray spectrometer analysis. The sawing tests were performed in the down-cutting mode. The sawing performances of the sawblades were evaluated in terms of cutting specific energy (SE), cutting force, axial force, and force ratio (ratio of tangential to normal force). The worn surfaces of the diamond segments were examined by scanning electron microscope micrographs. Upon evaluation of the experimental data, it was concluded that the determined performance criteria from laboratory sawing tests can aid manufacturers in the design of appropriate sawblades for specific rock types. Valid for the employed machining parameters, tested sawblade types, and workpiece properties, the results of a multiple linear regression analysis have indicated that the Sn percentage of the segment matrix, the diamond concentration, and the matrix hardness are the common dominant variables that affect cutting SE, axial force, and cutting force.

Mechanisms for Sawing of Refractory Bricks with Diamond Blades

Experimental studies were undertaken to investigate the mechanisms for circular sawing of refractory bricks with diamond segmented saw blades. Three kinds of diamond segments of different hardness were fabricated for the saw blades. The vertical and horizontal force components and the spindle power were measured in sawing. Based on the measurements of force and power, the specific energy and the normal force per diamond grit were obtained. The normal force per grit in the sawing of refractory bricks was found to be only 5% of the static compressive strength of diamonds used in the present study, but fractures of diamonds were still popular on the segment working surfaces after sawing. The power, horizontal force, and the specific energy were found to increase with segment hardness. The specific energy obtained from the measured power was basically comparable to the values obtained from a theoretical equation to calculate the specific energy associated with slurry erosion to the bond matrix of segments.