Diamond Grits Research Articles

Properties of nano-SiC/Ni composite coating on diamond surfaces

ABSTRACTA Ni coating and nano-SiC/Ni composite coating were prepared on diamond surfaces by an electro-co-deposition method. The surface morphology of plated diamond grit and the bonding state between diamond and Fe-matrix bond were characterised by the scanning electron microscopy and energy-dispersive spectroscopy (EDS). The flexural strength and wear resistance performance of the Fe-matrix bonded diamond tool bits were tested. The results showed that the nano-SiC/Ni composite coating possesses a smoother, finer, and denser microstructure when compared with a pure Ni coating. Furthermore, the nano-SiC/Ni composite coating on diamond surfaces improved the flexural strength and wear resistance of Fe-matrix bonded diamond tool bits. The EDS analysis indicated that the chemical combination between diamond grits and Fe-matrix bonding was formed, thereby the mechanical properties of Fe-matrix bonded diamond tool bits were enhanced.

Precision machining of ‘water-drop’ surface by single point diamond grinding

With good prospect for machining functional surfaces on hard and brittle materials, single point diamond grinding (SPDG) has been applied, but its wider application still need more effort and development. In the present work, an appropriate dressing method is firstly proposed to obtain a sharp edge on a fine grit diamond wheel. With the prepared wheel, a designed ‘water-drop’ surface is machined by single point diamond grinding (SPDG), with the integration of the rotary B axis. Based on the proposed compensation method, the form accuracy and surface finish of the machined functional surface reaches 0.64μm (PV), 6nm (Sa) for the Ф20mm ‘water-drop’ surface on binderless tungsten carbide.

Analytical and experimental investigation of the delamination during drilling of composite structures with core drill made of diamond grits: X-ray tomography analysis

Among the various forms of material damage, exit-ply delamination has been identified as one of the most deleterious damage processes associated with drilling fibre-reinforced plastics. The thrust force has been cited as the primary cause for drilling-induced exit-ply delamination. Only one analytical model for the prediction of the critical thrust force responsible for delamination using core drills can be found in the literature. In this study, a realistic model to predict critical thrust force responsible for drilling-induced exit-ply delamination in a multi-directional carbon fibre-reinforced plastic laminate with core drill has been proposed. A comparison between the proposed model, literature model as well as the experimental tests conducted during punching tests is presented. The proposed model is found to correlate well with experimental punching tests. In fact, the maximum relative errors recorded between the experimental values of the critical thrust force and the measured values are around 15%. Micro-tomography experiments have also been conducted that capture the drilling-induced damage in multi-directional carbon fibre-reinforced plastics in great detail. The X-ray images highlight the difficulty in controlling the thickness of the uncut plies located under the core drill during punching tests that can be attributed to some deviations in predictions of critical thrust force. Postmortem examination of the blind holes after punching tests also confirms the presence of a net delamination near the vicinity of the nominal diameter of the core drill, which correlates well to the hypothesis of the analytical model.

Challenges in brazing large synthetic diamond grit by Ni-based filler alloy

Large size D711 synthetic single crystal diamonds are vacuum brazed with medium carbon steel using a Ni-Cr-Fe-B-Si alloy and inherent difficulties are critically investigated. Although, the alloy shows appreciable wetting on diamond at the brazing temperature of 1050°C, micro-cracks develops and pronounces at the bond level in all as-brazed samples. The crack is not arrested even by using cooling rate, as slow as 5°C/min. The large difference in Young’s modulus and thermal expansion coefficient of the substrate, alloy and grit results in unfavorable tensile residual strain on diamond at bond level, causing detrimental stress. Formation of a partially coherent chromium iron carbide phase is identified which seems to facilitate the micro-crack formation under residual stress. The residual stress distribution at the interface region is mapped through finite element analyses. No noticeable difference in the strength of joint is recorded on reducing the cooling rate, up to 5°C/min. Failure pattern of grits suggests a predominant bond-level breakage of diamond grits, indicating prevalence of residual stresses at bond level. The (110) crystallographic plane of diamond suffers significant graphitization at higher temperatures, even under a very high vacuum environment.

Vacuum Brazing Diamond Grits with Cu-based or Ni-based Filler Metal

Diamond grits were brazed using Cu-Sn-Cr and Ni-Cr-B-Si filler metals, and the brazed grits were examined for microstructure (SEM, EDS, XRD), microhardness, and compression strength. Results showed that the microstructure of the Cu-based filler metal was uniform and consisted of α-Cu + (α-Cu + δ). Its wettability to the diamond was better than Ni-based filler due to the formation of a thin carbide reaction layer that improved the bond strength between the diamond and steel. The Cu-based filler led to reduced thermal damage to the diamond. The Cr in the filler metal diffused to the steel substrate to form a reaction layer at the filler/steel substrate interface. The microhardness of the Ni filler metal (810-830 HV0.3) was significantly higher than that of Cu filler metal (170-230 HV0.3). The compressive load values of the diamond grits brazed with Cu-based or Ni-based filler metal were 93.7 and 49.2% of the original diamond, and the TI values were 83.7 and 59.8% of the original diamond. Grinding experiments for failure mode in monolayer tools revealed that the tools brazed with Cu-based filler metal had a lower macro-fracture ratio than those brazed using the Ni-based filler.

Study of Ti-coated diamond grits prepared by spark plasma coating

A new method for coating diamond grits with metallic layers, referred to as spark plasma coating (SPC), was introduced in this paper. By controlling the Ti powders content in the mixture of diamond grits and Ti powders, the Ti-coated diamond grits were prepared in a spark plasma sintering system. The coatings were chemically bonded with diamond grits, which were constituted with the TiC and elemental Ti phases. When the mixture containing 10wt% Ti powders was treated at 800°C for 60min, the compressive fracture strength and toughness index of the prepared Ti-coated diamond grits were higher than in the cases of the raw diamond grits by 15.7% and 6.4%, respectively.

Analysis of grit interference mechanisms for the double scratching of monocrystalline silicon carbide by coupling the FEM and SPH

Three-dimensional twice scratching and double scratching of monocrystalline silicon carbide with two cone-shaped grains were simulated by coupling the finite element (FEM) and smoothed particle hydrodynamics (SPH) to resolve the mesh distortion problem caused by using the FEM. Twice-scratching experiments were performed under three different conditions to validate the coupled finite element (FE) and SPH model in the scratching simulation with two diamond grits. The experimental results were compared to the simulation results. For twice scratching, the simulation results conform with the experimental results, indicating the validity of the coupled FE and SPH model. Thus, the coupled FE and SPH model was used to simulate the double-scratching process under different conditions. The results of the double-scratching simulation showed that the interference damages in the scratching process occurred under three circumstances: the interference of lateral cracks, the interference of lateral cracks and plastic damage, and the interference of plastic damage. The influence of distance on the interference damage of the two diamond grits in the Y-direction was analysed. The changes in the maximum depth and width in the interference region and the scratching force with the distance of the two grains in the Y-direction are illustrated.

Formation of TiC via interface reaction between diamond grits and Sn-Ti alloys at relatively low temperatures

In this paper, interfacial reaction between diamond grit and Sn-6Ti alloy was systematically studied at brazing temperatures from 600 to 1030°C. A thin and uniform layer of scallop-like nano-sized TiC grains was formed after brazing for 30min at 600°C, and interfacial TiC grains subsequently coarsened as brazing temperature increased to 740 and 880°C. Strip-like columnar TiC grains in a bilayer structure was further grown as brazing temperature increased to 930°C. After brazing at 1030°C, a dense layer of columnar TiC grains were formed. Based on the TEM micrographs of interfacial TiC, the formation and evolution of the growth morphologies of interfacial TiC was believed to be controlled by the diffusion of C flux from diamond grits, which is dependent on the brazing temperatures.

Mechanisms of material removal and subsurface damage in fixed-abrasive diamond wire slicing of single-crystalline silicon

Single-crystal silicon was sliced using a newly developed high-speed fixed-abrasive dicing wire saw. The effects of diamond grit size, wire speed, and number of slicing cycle on the surface roughness and subsurface damage of the workpiece were investigated by surface profiling, Raman spectroscopy and cross-sectional transmission electron microscopy. It was found that by using finer diamond grits and increasing the sawing cycles, the depth of micro dents and saw marks was reduced significantly, and in turn, the surface roughness was improved. A transition from brittle mode to ductile mode machining was confirmed from chip morphology observation when reducing the grit size. The subsurface damaged layers were composed of amorphous layers, dislocated layers with grain boundaries, as well as micro cracks. The smooth surface regions were dominated by amorphous silicon; while within the saw marks, a mixture of amorphous and metastable silicon phases was detected. Inside the micro dents, however, single-crystal silicon was predominant. Furthermore, the significance of silicon amorphization and poly-crystallization was strongly dependent on the wire speed. The higher the wire speed, the less the amorphous and polycrystalline layer. The present study provides comprehensive insights into the surface formation mechanism which is important for process optimization of high-speed and low-damage slicing of single-crystal silicon.

Spectroscopic analysis of microdiamonds in ophiolitic chromitite and peridotite

Microdiamonds ∼200 μm in size, occurring in ophiolitic chromitites and peridotites, have been reported in recent years. Owing to their unusual geological formation, there are several debates about their origin. We studied 30 microdiamonds from 3 sources: (1) chromitite ore in Luobusa, Tibet; (2) peridotite in Luobusa, Tibet; and (3) chromitite ore in Ray-Iz, polar Ural Mountains, Russia. They are translucent, yellow to greenish-yellow diamonds with a cubo-octahedral polycrystalline or single crystal with partial cubo-octahedral form. Infrared (IR) spectra revealed that these diamonds are type Ib (i.e., diamonds containing neutrally charged single substitutional nitrogen atoms, N s 0 , known as the C center) with unknown broad bands observed in the one-phonon region. They contain fluid inclusions, such as water, carbonates, silicates, hydrocarbons, and solid CO 2 . We also identified additional microinclusions, such as chromite, magnetite, feldspar (albite), moissanite, hematite, and magnesiochromite, using a Raman microscope. Photoluminescence (PL) spectra measured at liquid nitrogen temperature suggest that these diamonds contain nitrogen-vacancy, nickel, and H2 center defects. We compare them with high-pressure–high-temperature (HPHT) synthetic industrial diamond grits. Although there are similarities between microdiamonds and HPHT synthetic diamonds, major differences in the IR, Raman, and PL spectra confirm that these microdiamonds are of natural origin. Spectral characteristics suggest that their geological formation is different but unique compared to that of natural gem-quality diamonds. Although these microdiamonds are not commercially important, they are geologically important in that they provide an understanding of a new diamond genesis.

Diamond wheel wear mechanism and its impact on the surface generation in parallel diamond grinding of RB-SiC/Si

The diamond wheel wear mechanism and its impact on the surface generation of RB-SiC/Si carbide under parallel grinding were investigated. The machined surface was mainly characterized by surface fracture and diamond grits scratched plastic grooves, and the surface finish of the machined RB-SiC/Si improved with decreasing feed rate. But the non-uniform surface appeared due to the varied material removal rate at different radial position for a certain workpiece. Both macro- and micro-wheel wear occurred during grinding, and the macro-wheel wear appeared in the form of profile deviation and rapid loss of sharp edge, which contributed to the appearance of cone shape at the center of workpiece. Power spectrum analysis by Fast Fourier Transformation (FFT) confirmed the significant influence of micro-wheel wear on surface generation, which involved random diamond grit splintering, abrasive flattening, grain dislodgement and graphitization.

Study on diamond dressing for non-uniformity of pad surface topography in CMP process

Diamond dressing process is critical in conditioning pad surface topography before and after chemical mechanical planarization/polishing (CMP) process for integrated circuit (IC) fabrication. This paper addresses a kinematic model of diamond dressing effect on the profile of pad cutting rate (PCR) with a ring-type diamond dresser through both simulation and experiments. In this kinematic model, the cutting locus distribution, relative velocity of diamond grits on a pad surface, and sliding time have been described as significant factors for non-uniformity of pad surface topography. Moreover, the speed ratio between the diamond dresser and the polishing pad has been investigated with respect to the center distance of the pad and the diamond dresser by the developed method. The model has been verified by experiments of diamond dressing of pad. Experimental results show that the dressing marks and pad cutting rate on the pad surface follow the same trend as simulation results and the final pad surface is obtained as a concave shape. Results of this study can be applied on diamond dressing of pads used in CMP and furthermore can be extended to investigate an optimal diamond dressing process for semiconductor fabrication.

Surface Damage Mechanism of Monocrystalline Si Under Mechanical Loading

Single-point diamond scratching and nanoindentation on monocrystalline silicon wafer were performed to investigate the surface damage mechanism of Si under the contact loading. The results showed that three typical stages of material removal appeared during dynamic scratching, and a chemical reaction of Si with the diamond indenter and oxygen occurred under the high temperature. In addition, the Raman spectra of the various points in the scratching groove indicated that the Si-I to β-Sn structure (Si-II) and the following β-Sn structure (Si-II) to amorphous Si transformation appeared under the rapid loading/unloading condition of the diamond grit, and the volume change induced by the phase transformation resulted in a critical depth (ductile–brittle transition) of cut (∼60 nm ± 15 nm) much lower than the theoretical calculated results (∼387 nm). Moreover, it also led to abnormal load–displacement curves in the nanoindentation tests, resulting in the appearance of elbow and pop-out effects (∼270 nm at 20 s, 50 mN), which were highly dependent on the loading/unloading conditions. In summary, phase transformation of Si promoted surface deformation and fracture under both static and dynamic mechanical loading.

An Assessment of Burs Designed to Cut Zirconia

Objective: Zirconia is increasingly being used in restorative dentistry but its removal is often a difficult procedure due to its resistance to cutting with conventional diamond burs. Zirconia cutting burs have been developed and this study aims to compare 4 such burs. Methods: 35 experienced restorative dentists selected from our Practice Based Network (PBN) were asked to evaluate the cutting of a 1 mm groove into zirconia using 4 burs A (Meisinger), B (ZR2-1 experimental bur from DIATECH), C (Komet) & D (DIATECH Z-Rex, a bur designed with enhanced bonding of diamond grit to bur shank). Responses regarding cutting time, performance and wear were recorded. Results: For best cutting times and also overall performance D performed best and C the worst, with little difference between burs A and B. Bur C also performed least well for wear on the bur. Conclusion: The newly designed zirconia cutting bur DIATECH Z-Rex with enhanced bonding of diamond grit performed best in the analysis by the 35 dentists.

The effects of temperature curves on the diamond/Ni-Cr interfacial properties in high-frequency induction brazing

The present study alters the temperature characteristics during high-frequency induction brazing of diamond grits and investigates their effects on the properties of the diamond/brazing alloy interface. The high-frequency induction brazing was conducted in a vacuum using Ni-Cr as active filler alloy. An active temperature range was identified for the brazing of high-quality diamond tools. This temperature range, coupled with long heating time, favours the wetting of filler alloy to diamonds, and the chemical reactions and element diffusion at the diamond/alloy interface, but reduces the static compressive strength of the diamonds. If the temperature is slowly raised, the protrusion height and location of brazed diamonds can be more precisely controlled. Brazed diamonds with 30%-50% protrusion are optimal for cutting.

The effects of temperature curves on the diamond/Ni-Cr interfacial properties in high-frequency induction brazing

The present study alters the temperature characteristics during high-frequency induction brazing of diamond grits and investigates their effects on the properties of the diamond/brazing alloy interface. The high-frequency induction brazing was conducted in a vacuum using Ni-Cr as active filler alloy. An active temperature range was identified for the brazing of high-quality diamond tools. This temperature range, coupled with long heating time, favours the wetting of filler alloy to diamonds, and the chemical reactions and element diffusion at the diamond/alloy interface, but reduces the static compressive strength of the diamonds. If the temperature is slowly raised, the protrusion height and location of brazed diamonds can be more precisely controlled. Brazed diamonds with 30%-50% protrusion are optimal for cutting.

The Material Removal Mechanism of Monocrystal SiC Scratching by Single Diamond Grit with Different Tip Radius

The Material Removal Mechanism of Monocrystal SiC Scratching by Single Diamond Grit with Different Tip Radius

Precision Surface Grinding of Silicon Carbide

Silicon carbide (SiC) is well known for its excellent material properties, high durability, high wear resistance, light weight and extreme hardness. Among the engineering applications of this material, it is an excellent candidate for optic mirrors used in an Airbone Laser (ABL) device. However, the low fracture toughness and extreme brittleness characteristics of SiC are predominant factors for its poor machinability. This paper presents surface grinding of SiC using diamond cup wheels to assess the performance of diamond grits with respect to the roughness produced on the machined surfaces and also the morphology of the ground work-piece. Resin bonded diamond cup wheels of grit sizes 46 µm, 76 µm and 107 µm; depth of cut of 10 µm, 20 µm and 30 µm; and feed rate of 2 mm/min, 12 mm/min and 22 mm/min were used during this machining investigation. It has been observed that the 76 grit performs better in terms of low surface roughness value and morphology.

Experimental study on the single grit interaction behaviour and brittle–ductile transition of grinding with a diamond micro-grinding tool

This study presents new information on single grit interaction behaviour and its brittle–ductile transition in micro-grinding single crystal silicon using a single grit diamond tool. A model to describe the energy interaction between the cutting behaviour of a single grit and the workpiece in micro-grinding is established based on the single grit geometry model, which was indicated in Fig. 1a, the critical condition of the volume of material removed and the conservation of energy. The tip angle of the single-point diamond tool has been considered. To reveal the material removal mechanism of micro-grinding, a series of scratching experiments, which conducted with a low cutting speed (0.036 to 0.6 m/s), have been performed in this study. The fractures of the micro-grooves machined using single-point diamond tools have been examined by a microscope and a surface profilometer, thus revealing different processing modes (brittle and ductile). The variation curves of the fracture length c have been presented on the condition of different tool tip angles θ (60° and 120°). It is found that the fracture size of grooves machined by a grit with a blunt angle is comparatively larger than that of a grit with a sharp angle for the same scratching parameters. The scratching speed v and penetration depth p0 have a direct effect on the fracture length c, which increases obviously with the rising of v and p0. The critical condition has been investigated based on the experimental results; the blunt grit (with a larger tip angle: θ = 120°) and the sharp grit (with a smaller tip angle: θ = 60°) have different brittle–ductile transitions and different critical cutting depths, which are 334 nm (θ = 60°) and 607 nm (θ = 120°), respectively. The effects of the scratching speed v are investigated. The brittle–ductile transitions of the different scratching speeds have been compared. The relationship between the fracture length c and the volume of material removed in unit time V has been discussed; V is an important measuring constant for the fracture formation and critical ductile cutting condition. This study reveals the mechanism of the single grit interaction in micro-grinding with an ultra-small grinding tool and provides theoretical and experimental validation for ductile micro-grinding of single crystal silicon.

In vitro assessment of cutting efficiency and durability of zirconia removal diamond rotary instruments

Statement of problemRecently, zirconia removal diamond rotary instruments have become commercially available for efficient cutting of zirconia. However, research of cutting efficiency and the cutting characteristics of zirconia removal diamond rotary instruments is limited. PurposeThe purpose of this in vitro study was to assess and compare the cutting efficiency, durability, and diamond rotary instrument wear pattern of zirconia diamond removal rotary instruments with those of conventional diamond rotary instruments. In addition, the surface characteristics of the cut zirconia were assessed. Material and methodsBlock specimens of 3 mol% yttrium cation-doped tetragonal zirconia polycrystal were machined 10 times for 1 minute each using a high-speed handpiece with 6 types of diamond rotary instrument from 2 manufacturers at a constant force of 2 N (n=5). An electronic scale was used to measure the lost weight after each cut in order to evaluate the cutting efficiency. Field emission scanning electron microscopy was used to evaluate diamond rotary instrument wear patterns and machined zirconia block surface characteristics. Data were statistically analyzed using the Kruskal-Wallis test, followed by the Mann-Whitney U test (α=.05). ResultsZirconia removal fine grit diamond rotary instruments showed cutting efficiency that was reduced compared with conventional fine grit diamond rotary instruments. Diamond grit fracture was the most dominant diamond rotary instrument wear pattern in all groups. All machined zirconia surfaces were primarily subjected to plastic deformation, which is evidence of ductile cutting. Zirconia blocks machined with zirconia removal fine grit diamond rotary instruments showed the least incidence of surface flaws. ConclusionsAlthough zirconia removal diamond rotary instruments did not show improved cutting efficiency compared with conventional diamond rotary instruments, the machined zirconia surface showed smoother furrows of plastic deformation and fewer surface flaws.