Conical Diamond Research Articles

Brittle-Ductile Threshold in Lithium Disilicate under Sharp Sliding Contact.

Computer-aided design (CAD)/computer-aided manufacturing (CAM) milling and handpiece grinding are critical procedures in the fabrication and adjustment of ceramic dental restorations. However, due to the formation of microfractures, these procedures are detrimental to the strength of ceramics. This study analyzes the damage associated with current brittle-regime grinding and presents a potential remedy in the application of a safer yet still efficient grinding regime known as "ductile-regime grinding." Disc-shaped specimens of a lithium disilicate glass-ceramic material (IPS e.max CAD) were obtained by cutting and crystallizing the lithium metasilicate CAD/CAM blanks (the so-called blue blocks) following the manufacturer's instructions. The discs were then polished to a 1 µm diamond suspension finish. Single-particle micro-scratch tests (n = 10) with a conical diamond indenter were conducted to reproduce basic modes of deformation and fracture. Key parameters such as coefficient of friction and penetration depth were recorded as a function of scratch load. Further, biaxial flexure strength tests (n = 6) were performed after applying various scratch loads to analyze their effects on ceramic strength. Scanning electron microscopy (SEM) and focused ion beam (FIB) were used to characterize surface and subsurface damage. Statistical analysis was performed using one-way analysis of variance and Tukey tests. While the SEM surface analysis of scratch tracks revealed the occurrence of both ductile and brittle removal modes, it failed to accurately determine the threshold load for the brittle-ductile transition. The threshold load for brittle-ductile transition was determined to be 70 mN based on FIB subsurface damage analyses in conjunction with strength degradation studies. Below 70 mN, the specimens exhibited neither strength degradation nor the formation of subsurface cracks. Determination of the brittle-ductile thresholds is significant because it sets a foundation for future research on the feasibility of implementing ductile-regime milling/grinding protocols for fabricating damage-free ceramic dental restorations.

Substrate dependent cracking behavior of CrAlN coatings

SummaryThe present study investigated the effect of substrate deformation behavior on crack resistance of CrAlN coatings under quasi‐static and cyclic loads using nanoindentation. (Cr47Al53)N coatings were deposited on cemented carbide WC‐Co and high‐speed steel HS652C substrates through physical vapor deposition (PVD) und characterized. In order to study the coating cracking behavior, the coated substrates were subjected to quasi‐static nanoindentations with indentation force Fmax = 1 N, Fmax = 1.5 N and Fmax = 2 N. Moreover, the crack resistance under cyclic loading with frequency f = 0.16 Hz was analyzed at F = 1 N and F = 1.5 N after n = 900 cycles. A conical diamond indenter was used for the tests. At the end, the indentation imprints were analyzed by scanning electron microscopy (SEM). The substrate dependency was apparent in cracking behavior of the coating. Albeit the lower indentation depth compared to the variant with HS6‐5‐2C substrate, the CrAlN coating on WC‐Co substrate showed surface cracks under quasi‐static and cyclic loading. These cracks on the coated surface were absent in the variant with HS6‐5‐2C substrate. This could be related to higher resistance of cemented carbide substrates against plastic deformation, prompting earlier crack initiation in CrAlN coating for effective energy dissipation during indentation.

Fundamental abrasive contact at high speeds: Scratch testing in experiment and simulation

The understanding and experimentation of abrasive wear mechanisms at high speeds is still poorly investigated in literature. This is mainly due to a lack of suitable, well-instrumented test rigs for fundamental, single abrasive wear events. Standard scratch tests, which are often utilized for studies of abrasion phenomena, operate in the low-speed range up to some mm/s, while applications suffering from abrasive wear often operate at speeds exceeding 1 m/s (e.g., rolling, grinding, machining).Numerical approaches, especially particle-based methods, allow the simulation of such fast deformation processes, but rely on hardening models that require a precise knowledge of material parameters. Thus, the Johnson-Cook material model was parametrized using data from high-speed compression tests of pure aluminum. A series of scratch tests with increasing depths were then simulated using the particle-based Material Point Method (MPM). Experimentation was done on a pendulum scratch test rig equipped with a Rockwell C diamond cone. By adjusting the balance point of the swing arm of ∼1 m length, a velocity of 6.8 m/s was achieved at its tip as measured with a high-speed camera. Scratches of several depths were performed, and their force signals acquired. Post-test analyses comprised topography measurements and EBSD on cross-sections of the scratches to investigate the microstructural changes due to the high-speed wear event.Scratch topographies and abrasive mechanisms compared favorably between experiment and simulation for the aluminum. The extent of strain hardening was significantly reduced compared to low-speed experiments. The calibration of the high-speed force sensor was successful and now allows the investigation of new alloys and determination of material parameters under high-speed abrasive conditions.

Comparison of extensions of plastic zones under conical Indentation to a semi-infinite block with the aid of finite Element analysis (fea) and slip-line field (slf) theories

Every metal cutting process is associated with the combination of indentation processes. Thus, studying indentation has a great importance in mechanics of metal cutting process. The present work deals with the indentation of a conical diamond point indenter to a semiinfinite block of mild steel. In indentation process, some portion of the block is plastically deformed. The present work investigates zone of extensions of plastic zone for different types of indenters having varying cone angles through finite element analysis and compare the results with Slip-line field approaches. The present work considers semi-apex angle of the cone to be greater than 45°.

Deformation and removal mechanism of single crystal gallium nitride in nanoscratching

Understanding the deformation mechanism of a brittle material under mechanical loading is of value for unveiling the material removal in an abrasive machining process. In this work, instrumented nanoscratching was performed on the (0001) plane of single crystal gallium nitride (GaN) using a conical diamond indenter and the scratch-induced surface/subsurface deformation patterns were characterized by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A finite element model of scratching was established to relate stress distribution and deformation patterns. The stress threshold for the elastic-plastic deformation transition of the crystal was found being relatively high in comparison to single crystal silicon and gallium oxide. The plastic deformation in the GaN sublayer was dominated by slip, dislocation and lattice distortion under relatively low normal loads, but those defects were accompanied with grain rotation when the load was sufficiently high. The thickness of the damage layer was directly related to the ratio of lateral force to normal force during scratching. Such a force ratio can be used as an indicator for controlling the damage layer thickness during abrasive machining, thus providing a valuable guidance for developing the optimal parameters of an ultraprecision abrasive machining process.

Diamond Cone for $${{\mathfrak {sl}}}(m,n)$$

In this paper, we study the shape and the reduced shape algebra for the Lie superalgebra \({\mathfrak {sl}}(m,n)\). We define quasistandard Young tableaux, and they give a combinatorial basis for the reduced shape algebra, called the diamond cone. There is a natural bijective map from the set of semistandard tableaux with shape \(\lambda \) to the set of quasistandard tableaux with smaller shape: the diamond cone is compatible with the stratification of the reduced shape algebra.

Lapping performance of diamond cone array tool prepared by double bias assisted HFCVD

In this paper, the free-standing diamond (FSD) and microcrystalline diamond (MCD) film were etched by double-bias assisted hot filament chemical vapor deposition (HFCVD) to prepare two kinds of diamond cone array tools (DCATs) for precision processing. It is the first time to use free-standing diamond cone array tool (FSD-CAT) and microcrystalline diamond cone array tool (MCD-CAT) to perform the lapping processing experiment for monocrystalline silicon and to carry out the performance evaluation of DCAT. The surface roughness of the silicon lapped by FSD-CAT is 28.9 nm, and the surface roughness of the silicon lapped by MCD-CAT is 18 nm. By using the combination of both DCATs to lapped silicon, a smooth surface with a surface roughness of 5 nm is obtained. By comparing the surface roughness of monocrystalline silicon which lapped by diamond tools with and without etching, because of the smaller cross-section of the cones cut into the surface of monocrystalline silicon, DCAT can effectively reduce the Surface roughness of the silicon.

A theoretical model to predict the anisotropic characteristics in grinding of diamond conical indenter

Mechanical grinding of a high-precision diamond conical indenter is difficult due to the strong grinding removal rate anisotropy. In the existing literature, theoretical models have been established to predict the strength anisotropy of diamond on the (100), (110) and (111) planes, which provide a theoretical basis for the fabrication of pyramid diamond indenters, such as Berkovich, Vickers or Knoop indenters. However, investigations on the anisotropic characteristics in processing of diamond curved surface are rarely carried out. To solve the anisotropy problem in grinding of diamond conical indenter, this work contributes a theoretical model to predict the anisotropic characteristics in grinding of diamond cone face, and provides an effective method to optimize the grinding direction for enhancing the fabrication precision. Based on a proposed grinding-ability factor model, a general method is developed to analyze the grinding ability along different directions according to the formation process of the cone face. The results suggest that the optimized mechanical grinding direction can be determined by minimizing the standard deviation of the grinding-ability factors of the crystal planes. The proposed method is validated by grinding experiments on indenters, with the <100> or <111> orientation along the indenter axis. The experimental observations confirm that the optimized grinding direction can weaken the pyramid phenomenon, yielding a roundness error of 0.12 μm. In addition, the grinding removal rate-dependent roughness petal phenomenon is suppressed, which considerably enhances the conical surface quality.

Adhesion strength of Tii_xCx – DLC multilayer nanocomposite thin films coated by ion-plasma deposition on martensitic stainless steel produced by selective laser melting followed by plasma-nitriding and burnishing

[Ti0.2C0.8/a-C]40 multilayer thin films composed of forty pairs of TiC and pure carbon layers were formed on a selective laser melted (SLM) martensitic stainless steel by means of ion-plasma deposition process. SLM steel was pre-treated by one of the two following schemes: (1) oil quenching from 1040°C followed by heating to 480°C for 4 hours and air cooling (HT), finish milling (FM); (2) HT, FM, ion-plasma nitriding followed by burnishing. Mechanical failure mode and critical load Lc for damaging the coatings were determined using linear scratch tests performed at linearly-increased normal force. Indentation by conical diamond tip were carried out in order to asses an elastic recovery and energy dissipation coefficient defined as the ratio of plastic to total deformation energy. The scratch test results showed that the post-processing of the substrate strongly influenced the failure mode of the coating and increased the critical load from 320 mN to 920 mN. Indentation revealed that nitriding and burnishing before coating deposition increase the elastic recovery of the [Ti0.2C0.8/a-C]40 coating-substrate system from 24% to 68%. The energy dissipation coefficient drops from 79% to 45%.

Evaluation of the Microstructure, Tribological Characteristics, and Crack Behavior of a Chromium Carbide Coating Fabricated on Gray Cast Iron by Pulsed-Plasma Deposition.

The structural and tribological properties of a protective high-chromium coating synthesized on gray cast iron by air pulse-plasma treatments were investigated. The coating was fabricated in an electrothermal axial plasma accelerator equipped with an expandable cathode made of white cast iron (2.3 wt.% C–27.4 wt.% Cr–3.1 wt.% Mn). Optical microscopy, scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction analysis, microhardness measurements, and tribological tests were conducted for coating characterizations. It was found that after ten plasma pulses (under a discharge voltage of 4 kV) and post-plasma heat treatment (two hours of holding at 950 °C and oil-quenching), a coating (thickness = 210–250 µm) consisting of 48 vol.% Cr-rich carbides (M7C3, M3C), 48 vol.% martensite, and 4 vol.% retained austenite was formed. The microhardness of the coating ranged between 980 and 1180 HV. The above processes caused a gradient in alloying elements in the coating and the substrate due to the counter diffusion of C, Cr, and Mn atoms during post-plasma heat treatments and led to the formation of a transitional layer and different structural zones in near-surface layers of cast iron. As compared to gray cast iron (non-heat-treated and heat-treated), the coating had 3.0–3.2 times higher abrasive wear resistance and 1.2–1208.8 times higher dry-sliding wear resistance (depending on the counter-body material). The coating manifested a tendency of solidification cracking caused by tensile stress due to the formation of a mostly austenitic structure with a lower specific volume. Cracks facilitated abrasive wear and promoted surface spalling under dry-sliding against the diamond cone.

Cone Beam Computed Tomography Assessment of the Volume of Dental Tissue Removed During Endodontic Access.

The purpose of this study was to determine the volume of dental tissue removed during endodontic access preparation with cone-beam computed tomography (CBCT) comparing two different software. CBCT images of 20 teeth were obtained before and after endodontic access performed with spherical and conical diamond burs. The images were taken with i-CAT Precise system with 0.25 mm voxel size. Digital Imaging and Communications in Medicine (DICOM) images were loaded on two different software programs (Materialise® and InVersalius®), and a 3D reconstruction of the CBCT images was performed on both programs. The baseline volume (BV), and the final volume (FV) were obtained, and the lost tissue volume (LV) was calculated using the formula: LV=BV-FV. The t-test was used to compare initial and final volumes and also to compare the two programs, using a significance level of 5%. The volumetric data calculated for the Materialise and the InVesalius programs were, respectively: BV-mean of 441.79±85.08 mm3 and 442.01±84.83 mm3; FV-mean of 426.75±83.88 mm3 and 426.94±83.75 mm3; LV-mean of 15.04±4.32 mm3 and 15.07±4.16 mm3. No statistically significant difference was found in the volumes calculated by either program for initial, final, or removed tissue (P>0.05). However, there was a significant difference between the BV and LV calculated on the same program (P<0.05). Our in vitro study showed that CBCT was able to determine the volume of dental tissue removed in the endodontic access preparation of extracted human teeth, regardless of the software program used.

The Ultimate Load Estimation of Welded Joints of High-Strength Steels subject to Mechanical and Geometric Heterogeneity

In this paper we consider the problems arising in the numerical estimation of the ultimate load of welded joints of high-strength steels with slight hardening. The stress concentrator in the transition node from the deposited to the base metal is modeled based on the example of welding a roller wire on a plate made of high-strength steel. The use of welding wire with a yield point lower than that of the base metal allowed to simulate areas of the welded joint with heterogeneous mechanical properties. The geometry of three areas of the welded joint is studied, i.e. weld metal, heat-affected zone (HAZ) and the base metal. Mechanical properties of all three areas are determined by calculation and experimentally. For this purpose, it is proposed to consider the material in all sections as ideally elastic-plastic, and the yield strength is uniquely associated with the hardness in the indentation zone (a Rockwell diamond cone is used). Calculations of the inelastic indentation process by the finite element method (FEM) in axis-symmetric formulation allowed obtaining a linear relationship between the hardness and the yield strength with a coefficient of 0.418. Tests at a quasi-static three-point bend (with stretching in the surfacing area) were carried out on sample beams cut perpendicular to the direction of welding. The “force-deflection” diagrams are obtained and compared with the calculated curves (FEM in a three-dimensional formulation with an explicit consideration of the complex configuration of all sections and different yield stress in the areas determined by local hardness values). There is a good agreement between the calculated and experimental ultimate loads. The proposed method of the three-stage study (determination of local hardness, yield strength in the areas and the ultimate load) can be effectively used to assess the ultimate loads of the welded joints due to the low parametricity of the proposed models of materials inelastic deformation in areas for which it is impossible to manufacture standard samples for the study of mechanical properties. The experimental study of the strengthening effect of the seam with a stress concentrator in the form of an angle of 90 degrees on the value of the ultimate bending load showed that the removal of the deposited metal does not lead to an increase in the ultimate load of the welded joint when using the welding wire of low-carbon high-plastic steel.

Mechanical scribing test analysis of lateral ridges law on aluminum

In order to study the rule of lateral uplift of pure aluminum (purity is 99.999%) during mechanical scribing, based on the mechanical scribing test device, the tool tip angles are 80 °, 85 °, 90 °, 95 °, 100 ° The diamond cone cutter is used to perform mechanical scoring test on pure aluminum with a depth range of 5μm-25μm. Through the bump height detection analysis, lateral ridge height and groove depth - mathematical statistical relationship knife sharp corners, through the known parameters such as groove depth, groove on the bump height is pre-sentence, thereby pre-Groove play an important role in the control.

Improvement of Nb/Cu adhesion and increase of Nb crystal size by laser radiation

Adhesion of Nb thin film to Cu substrate and size of Nb crystal grains for RF cavities were studied depending on laser intensity and dose. Structures of Nb/Cu, obtained by magnetron sputtering with 500 ˚C (Nr.1) and 700 ˚C (Nr.2) deposition temperature, were irradiated by pulsed Nd:YAG laser. Four areas, irradiated with doses D1 = 5.6x1020, D2 = 8.8x1020, D3 = 1.76x1021 and D4 = 1.76x1022 phot/cm2, were studied. Delamination was investigated by scratching method using conical diamond indenter with force increased from 10 mN to 3.0 N. Characterization of the structure before and after the irradiation was performed using an optical microscope, AFM, SEM and XRD. Comparing with the non-irradiated area, the critical delamination force increased by 10% for sample Nr.2 and by 36% for sample Nr.1 at laser doses D2 and D4, respectively. It means that Nb coating layer of sample Nr. 1 is better than that of sample Nr.2. The decrease of average roughness of Nb layer by an order of magnitude was observed after the laser irradiation. The improvement of the structure adhesion was also observed and explained by the diffusion of Nb atoms into Cu through dislocations. The increase of Nb crystallites size from 20 to 35 nm was calculated using XRD data.

Local Fracture of Nanolaminates: Edge Chipping Test

The fracture resistance of domestic and foreign nanolaminate ceramics was studied by the EF (edge fracture) method. This method provides for indentor chipping of rectangular specimen edges, which permits evaluating such fracture resistance characteristics, as chipping resistance and edge toughness. There is no way of experimental determining the stress intensity factor effected as the penetration of a Vickers indentor into the polished specimen surface and measurement of crack sizes that are formed near the angles of its imprint. The influence of stress concentrations in the indentor–specimen surface contact zone on the fracture resistance of ceramics was assessed. Different test stress concentrations were produced with conical diamond indentors of different tip radii. Studies on domestic titanoaluminous carbide Ti3AlC2 specimens demonstrated that with a reduction in stress concentration levels (indentors with increasingly larger tip radii), its edge toughness grew to a smaller extent than that of Y2O3 and TS Mg-PSZ ceramics. It is indicative of the limited sensitivity of an examined material to stress concentrations on local fracture. The ratio of edge toughness determined with the indentors of maximum and minimum tip radii (in this case, 400 and 11 μm) can serve as a measure of its sensitivity (in comparison to this characteristic for examined materials). Note that the edge toughness of Ti3AlC2 ceramics is almost one-third as large than, e.g., that of Y2O3 ceramics and 1.6 times smaller than that of TS nonlinearly elastic zirconia Mg-PSZ.

Hardness and Wear Resistance of Dental Biomedical Nanomaterials in a Humid Environment with Non-Stationary Temperatures.

This study discusses a quantitative fatigue evaluation of polymer–ceramic composites for dental restorations, i.e., commercial material (Filtek Z550) and experimental materials Ex-nano (G), Ex-flow (G). Their evaluation is based on the following descriptors: microhardness, scratch resistance, and sliding wear. In order to reflect factors of environmental degradation conditions, thermal fatigue was simulated with a special computer-controlled device performing algorithms of thermocycling. Specimens intended for the surface strength and wear tests underwent 104 hydrothermal fatigue cycles. Thermocycling was preceded by aging, which meant immersing the specimens in artificial saliva at 37 °C for 30 days. Microhardness tests were performed with the Vickers hardness test method. The scratch test was done with a Rockwell diamond cone indenter. Sliding ball-on-disc friction tests were performed against an alumina ball in the presence of artificial saliva. A direct positive correlation was found between thermocycling fatigue and microhardness. The dominant mechanism of the wear of the experimental composites after thermocycling is the removal of fragments of the materials in the form of flakes from the friction surface (spalling). Hydrothermal fatigue is synergistic with mechanical fatigue.

Ductile-brittle transition detection in scratching of single crystal silicon using charged particle emissions

During machining of single-crystal silicon, material removal involves two modes ductile shear-based removal and brittle fracture-based removal. Ductile shear-based chip removal occurs when fracture is suppressed due to local stress conditions along with reduced chances of defect involvement and is desirable for achieving better surface integrity of the machined silicon wafer. In this work, we use charged particle emissions to identify mode of material removal (ductile or brittle) during scratching of a silicon wafer. Scratching tests were performed using a pin-on-disc tribometer setup with a conical diamond tip indenter, in which the wafer was held at an inclined position to achieve a varying-depth tapered scratch. The varying-depth scratch test was performed in such a manner that both ductile-to-brittle and brittle-to-ductile modes occur in a single scratch test. The charged particles emitted during the material deformation were collected using a Faraday plate mounted in the vicinity of the indenter and the intensity of the charged particles were measured using a sensitive femto/picoammeter. The scratch depth was measured using a 3D surface profiler and the mode of fracture was identified by examining crack density per unit length in a scanning electron microscope. These results were then correlated with the emission intensity signals. From the experimental results, a positive current intensity was observed for ductile mode of scratching and highly varying current intensity signal is observed during brittle mode of scratching. The results obtained were consistent over time and exhibited good repeatability. The present work indicates suitability of employing charge emission signals to detect mode of material removal during scratching of silicon. This work can be field-tested by conducting diamond turning experiments of silicon in real-time machining environment further testing the scope of use of charged particle emission to monitor real-time machining process.

Conical support for double-stage diamond anvil apparatus

ABSTRACTBoth micro-paired and conical support type double-stage diamond anvil cells (ds-DAC) were tested using a newly synthesized ultra-fine nano-polycrystalline diamond (NPD). Well-focused X-ray sub-micron beam and the conically supported 2nd stage anvils (micro-anvils) with 10 μm culet enable us to obtain good quality X-ray diffraction peaks from the sample at around 400 GPa. The relationship between confining pressure and sample pressure depends heavily on the initial height (thickness) of micro-anvils, the difference of a few micrometers leads to a quite different compression path. The conical support type is a solution to retain both enough thickness and strength of micro-anvils at higher confining pressure conditions. All conical support ds-DAC experiments terminated by the failure of the 1st stage anvil instead of 2nd one. The combination of ultra-fine NPD 2nd stage anvil and NPD 1st stage anvil opens a new frontier for measurement of the X-ray absorption spectrum above 300 GPa.

A Study of Scratch Speed Effects on Ductile–Brittle Transition in Silicon

A unique rotational double-taper scratching setup is used to study ductile brittle transitions in single crystal (100) p-type silicon using a conical diamond tool at room temperature and scratching speeds ranging between 0.1 m/s and 0.3 m/s. In such a setup, transition from brittle to ductile occurs twice in a single-tapered scratch, during tool entry and tool exit. A well-defined way to determine critical depth of cut via linear crack density per unit crack length is proposed. The scratches were studied using scanning electron microscopy (morphology) and white light interferometry (depth measurements). A comprehensive study of critical depth of cut, compiled from the literature together with data from this study, with scratching speeds from very low to high shows that critical depth of cut decreases from very low scratch speeds to medium scratch speeds and then increases again at very high scratch speeds. An inference from this study is that diamond turning should be conducted at higher cutting speeds than being undertaken today to make use of larger critical depths of cut.

Preliminarny studies on scratch resistance of the face shields surface of firefighting helmets

Nowadays, in rescue operations firefighters of the State Fire Service use firefighting helmets which protect their head. Type B helmets in accordance with PN EN 433 technical norm are most often used. The face shields of firefighting helmets are usually made of transparent polycarbonate. One layer of metalized coatings, usually made in PVD technology are often applied on the shield surface. Sometimes multi-layer and gradient coatings are also applied. The surface of a visor may get damaged. Surface damages limit the field of rescuer view, and also adversely influence on barrier properties of the shield. One of the utility criterion for face shields and glasses of firefighting helmets is scratch resistance. Comparative studies on scratch resistance of surface were performed. The test was conducted with the use of Rockwell diamond cone. Small differences in scratch resistance were shown. The mechanism of surface degradation due to scratch of studied shields were varied. The highest resistance against the indenter was obtained in case of the shield surface of the Kontekst helmet. The lowest surface degradation was observed for the helmet with the shield face covered by metalized coating - Gallet. The face shields of helmets without coating were characterized by higher dam-ages. The highest damage was obtained in case of the Kontekst helmet.