Diamond Indenter Research Articles

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.

The Dislocation- and Cracking-Mediated Deformation of Single Asperity GaAs during Plowing Using Molecular Dynamics Simulation

This work simulates the plowing process of a single asperity GaAs by diamond indenter using molecular dynamics simulations. The deformation mechanism of asperity GaAs is revealed by examining the topography evolution and stress state during the plowing. This work also investigates the origin of the influence of asperity size, indenter radius and plow depth on the deformation of the asperity GaAs. We observed the initiation and propagation of cracks up to the onset of fracture and the plastic activity near the indenter, obtaining more information usually not available from planar GaAs in normal velocity plowing compared to just plastic activity. The simulations demonstrated the direct evidence of cracking in GaAs induced by plowing at an atomic level and probed the origin and extension of cracking in asperity GaAs. This finding suggests that cracking appears to be a new deformation pattern of GaAs in plowing, together with dislocation-dominated plasticity modes dominating the plowing deformation process. This work offers new insights into understanding the deformation mechanism of an asperity GaAs. It aims to find scientific clues for understanding plastic removal performed in the presence of cracking.

Crack resistance, strength and dynamic fatigue of quartz fibers with copper coatings

Metallized coatings can significantly improve the operational properties of quartz fibers. The research was conducted to determine the crack resistance, strength and dynamic fatigue of optical fibers without any coating and with copper coatings. The microhardness of quartz fibers was measured by the diamond indentation of end surfaces. The stress intensity parameter K1cwas found from the A. Niihara semi-empirical dependence. The geometry of indentation and radial cracks was studied using a scanning electron microscope. The crack resistance of uncoated quartz turned out to be almost 3 times less as compared to the copper coating fiber, which is presumably due to the additive contribution of compressive stresses on fiber surfaces and quartz wetting with copper. Copper-coated optical fiber drawing increases the tensile strength, crack resistance and dynamic fatigue parameter, and it is the main resource for maintaining operation in the conditions of a statistical approach to structural strength. Comparative tests were conducted to check the optical fiber strength by two-point bending and axial tension methods. Experimental tests conducted to check the ultimate mechanical strength of quartz optical fibers showed a significant spread of data, which indicates the presence of cracks of various sizes in a brittle solid and is a characteristic feature of brittle fracture as suggested by the A. Griffiths theory. In addition, it was assumed that the chaotic distribution of defects and microcracks extends along the entire length of a brittle solid, a quartz optical fiber in this case. A statistical model based on the Weibull distribution was used to describe surface microcracks depending on the fiber length. As a result, Weibull graphs were plotted in coordinates connecting the probability of failure with the strength, fiber length and parameter describing the ultimate strength.

Study of some thermo-mechanical parameters in Se70Te30-xMx (x = 0, 2; M = Cd, Ag, and Zn) alloys

Vickers microhardness has been determined by performing micro-indentation experiments on Chalcogenide glasses (ChGs) of Se70Te30, and Se70Te28M2 (M = Cd, Ag, and Zn) alloys using micro-indentation and optical microscopic techniques. Vickers micro-hardness is directly observed by the diagonal lengths of the indentation marks of a pyramidal diamond indenter. Thermally-induced glass transition was noticed by the DSC technique. Mechanical property such as modulus of elasticity (E), is calculated by well-known empirical relations. The minimal energy of micro-void (Eh), micro void volume (Vh), and covalence character of the glassy system are discussed in terms of microhardness (Hv). Physical parameters i.e., overall mean bond energy, density, molar volume, and compactness have been also carried out.

Determination of in-plane anisotropy of rolled sheets, taking into account the effect of strain intensity

The results of experimental studies of the mechanical properties anisotropy of rolled sheets made of NKh260YD steel are presented. Tension was applied to flat specimens cut in directions of 0, 45, and 90 degrees with respect to the rolling direction. A dividing grid was applied to the samples with a diamond indenter in the area of the estimated length on an instrumental microscope. Based on the results of measurements of the samples linear dimensions before and after deformation in the places where the dividing grid was applied, the logarithmic deformations were calculated over the width and thickness of the sample in each of the considered sections. The results of measurements and calculations showed the uneven intensity of deformations in its various sections. For further processing, data in sections under conditions of uniform deformation were used. The anisotropy coefficients were determined as the ratio of logarithmic strains over the width and thickness of the sample. The tension was carried out in three stages, which made it possible to establish the dependences of the anisotropy coefficients on the strain intensity, which were used to assess the degree of in-plane anisotropy of the material under study. Graphic dependences are presented illustrating the nature of the change in the anisotropy coeffi cients and the degree of anisotropy of the material under study depending on the intensity of deformation. A significant dependence of the HX260YD steel planar anisotropy degree on the magnitude of the strain intensity is shown, which must be taken into account when developing technological processes for production of critical articles from anisotropic sheet material by plastic shaping operations.

Effect of Aging on the Microhardness of Different Resin-based Fluoride-releasing Fissure Sealants: An In Vitro Study

The aim of the present study was to evaluate the effect of aging on the microhardness score [Vickers hardness number (VHN)] of different resin-based fluoride-releasing sealants compared to non-fluoride resin-based sealants. A total of 48 extracted sound molars that were sectioned mesiodistally were used. In the current study, four types of sealants were compared: Group A, a resin-based non-fluoride-releasing pit and fissure sealant (Eco-S sealant) served as a control. Groups B, C, and D received resin-based fluoride-releasing pit and fissure sealants Helioseal F, Fissurit F, and Embrace™ WetBond, respectively. Subsequently, each group was further divided into immediate and aged subgroups. The samples had been evaluated regarding their microhardness using a pyramidal diamond indenter of a Vickers hardness test at two-time intervals: Immediately and after the aging process through thermocycling. There were no statistically significant differences between mean VHN and material types (p = 0.72). Aging appeared to significantly increase the mean VHN (p = 0.001). The interaction model between material type and time factor showed that the effect of aging differs by the material type, where the VHN of the Embrace™ group increased significantly after aging from 24.33 ± 5.60 to 31.70 ± 3.59 (p = 0.001). While there were no significant differences in the microhardness of commonly used fluoride-releasing fissure sealants, time appears to significantly increase the mean microhardness score (VHN), especially in the Embrace™ group. Embrace™ WetBond fissure sealant showed a significant improvement in the mean microhardness score (VHN) with time. However, clinical studies with long-term follow-up are needed to confirm our results.

АДГЕЗИОННЫЕ ХАРАКТЕРИСТИКИ ТОНКОПЛЕНОЧНОГО ПОКРЫТИЯ, ОСАЖДАЕМОГО ПРИ ФИНИШНОМ ПЛАЗМЕННОМ УПРОЧНЕНИИ

The methodology for determining adhesion characteristics of thin-film coatings applied from the vapor phase and used to protect parts against wear and corrosion has been considered. The study of adhesion properties, along with deter-mination of thickness, composition of elements, structure, physical-mechanical, and tribological characteristics, as well as wear coefficient, al-lows evaluating and selecting the optimal coat-ing and best technology for its application for a specific industrial application. On the example of studying DLCPateks diamond-like coating of aC:H/a-SiOCN system deposited during final plasma hardening, adhesion characteristics were assessed according to ISO 20502:2005 by scratch testing and according to ISO 26443:2008 by indentation of Rockwell diamond indenter. The first tests were performed to determine the load at which the depth of penetration of the indenter into the coating - substrate composition stops growing smoothly, which characterizes the moment of destruction of the coating. The ratio of the load on the indenter, determined at the end of the passage of the coating thickness, to the load of occurrence of the first cracks or delamination, in these tests is conventionally called the adhesion coefficient. The influence of the coating thickness on the adhesion coefficient has been studied. The tests associated with the use of a Rockwell diamond indenter punch qualitatively evaluate the adhesion properties of the coating by comparing the obtained and normalized impressions. The results of the tests proved improved adhesion characteristics of DLCPateks coating.

Determination of the critical tensile stress of sapphire by spherical indentation with additional lateral forces

Abstract The comprehensive mechanical characterisation of thin films and surfaces is very important for a suitable optimisation of protection layers and layer systems. The Young’s modulus and the yield strength are widely accepted material parameters which can be determined by spherical nanoindentation in normal direction. This article reports on the determination of a further parameter, the critical tensile stress, by spherical nanoindentation with additional lateral forces. The critical tensile stress was determined for sapphire. It will be shown that the results obtained with two different nanoindentation devices equipped with spherical diamond indenters of different radii agree with less than 10% deviation.

Nanoindentation Response of Ion-Irradiated Fe, Fe-Cr Alloys and Ferritic-Martensitic Steel Eurofer 97: The Effect of Ion Energy

Nanoindentation of ion-irradiated nuclear structural materials and model alloys has received considerable interest in the published literature. In the reported studies, the materials were typically exposed to irradiations using a single ion energy varying from study to study from below 1 MeV to above 10 MeV. However, systematic investigations into the effect of self-ion energy are still insufficient, meaning that the possibilities to gain insight from systematic energy variations are not yet exhausted. We have exposed pure Fe, ferritic Fe-9Cr, martensitic Fe-9Cr and the ferritic-martensitic reduced-activation steel Eurofer 97 to ion irradiations at 300°C using 1, 2 and 5 MeV Fe2+ ions as well as 8 MeV Fe3+ ions and applied nanoindentation, using a Berkovich diamond indenter, to characterize as-irradiated samples and unirradiated references. The effect of the ion energy on the measured nanoindentation response is discussed for each material. Two versions of a primary-damage-informed model are applied to fit the measured irradiation-induced hardening. The models are critically compared with the experimental results also taking into account reported microstructural evidence. Related ion-neutron transferability issues are addressed.

The electrochemical corrosion behaviour of Ti-48Al-2Nb-0.7Cr-0.3Si alloy in 3.5%NaCl

Titanium aluminides (TiAl) have attracted industrial interest, particularly for high temperature applications owing to their promising mechanical properties. Due to the application of these materials to the marine environment it is therefore important to understand their performance under such conditions. In this study, the corrosion behaviour of Ti-48Al-2Nb-0.7Cr-0.3Si alloy produced by vacuum arc melting was investigated using the potentiodynamic polarization method. The corroded surface and Ti-Al phases were investigated by scanning electron microscopy (SEM), optical microscopy, and X-ray diffraction (XRD). Hardness was examined by a Vickers micro hardness tester with a diamond indenter. Pitting was observed to occur within the surface defects and caused severe corrosion.

Experimental study of strength and fracture toughness of laser-blasted glass

The use of glass in structural applications has been increasing during last years. Nevertheless, the generalized use of surface-modified bearing glass is precluded by the lack of knowledge about their mechanical performance. This experimental investigation carries out the assessment of the fracture toughness and strength of glass subjected to laser blasting. Annealed glass and heat strengthened glass plates were subjected to mid-infrared laser surface treatment to increase the surface roughness and improve the slip resistance in wet conditions. The fracture toughness and fracture surface energy were experimentally determined from the observed radial cracks after micro-indentation with a pyramidal diamond indenter, and the results were analyzed in correlation to the laser processing conditions and the obtained surface roughness. The Weibull graph and the cumulative failure probability of the as-received and laser-modified glass were obtained by the four-point bending test.

The pre-stress scratching test investigation on silicon carbide ceramics

Based on the theory of pre-stress machining, In this paper the pre-stress scratching test was carried out on SiC ceramics, and the single-point diamond indenter moved with uniform speed under constant normal load. Combining with acoustic emission testing, the acoustic emission signal, the depth of scratch and the damage of surface / subsurface were analyzed under different pre-stress. The results showed that the existence of pre-stress can shorten the depth of median cracks and reduce the surface / sub-surface damage when adopting pre-stress machining method to study the machining of ceramic materials, moreover, with the increasing of pre-stress to a certain extent, the depth of median cracks were decreased and the propagation length of lateral cracks were shortened.

In-situ SEM cyclic nanoindentation of pre-sintered and sintered zirconia materials

Efficient diamond machining of zirconia requires a comprehensive understanding of repetitive diamond indentation mechanics. This paper reports on in-situ cyclic nanoindentations of pre-sintered and sintered zirconia materials performed inside a scanning electron microscope (SEM). In-situ SEM imaging of cyclic indentation processes and high-magnification SEM mapping of indentation imprints were conducted. The elastic and plastic behaviors of pre-sintered and sintered zirconia materials were investigated as a function of the cyclic nanoindentation number using the Sakai and Sakai-Nowak models. For pre-sintered zirconia, cyclic nanoindentation induced quasi-plastic deformation, causing localized agglomeration of zirconia crystals with microcracks and large cracking along the indentation edge. Severely compressed, fragmented, and pulverized zirconia crystals and smeared surfaces were also observed. For sintered zirconia, shear bands dominated quasi-plastic deformation with the formation of edge pile-ups and localized microfractures occurred at indentation apex and diagonals. All elastic and plastic behaviors for pre-sintered and sintered zirconia materials revealed significantly microstructure-dependent. Pre-sintered zirconia yielded significantly lower contact hardness, Young's moduli, resistance to plasticity, elastic deformation components, and resistance to machining-induced cracking, and higher elastic and plastic displacements than sintered state. Meanwhile, all the behaviors for the two materials were independent from the cyclic nanoindentation number. A model was proposed for cyclic nanoindentation mechanics, revealing their cyclic indentation-induced microstructural changes in the two zirconia materials. This study advances the fundamental understanding of nanoindentation mechanics of zirconia materials.

Wear of bulk-fill resin composites

ObjectiveBulk-fill resin composites are a special group of restorative materials designed to reduce chair time needed to insert a direct composite restoration. However, other factors determine the clinical success of a restorative material. Clinically the major reasons for failure of direct restorations are secondary caries and fracture of the restoration or the tooth itself. In the long-term composite resin restorations in posterior teeth may be prone to wear. As bulk-fill materials have their own composition that will determine their mechanical properties, the wear resistance may be affected as well. The aim of this in vitro study was to evaluate the wear of bulk-fill composites in comparison with a conventional hybrid composite. The null hypothesis was that there are no differences between the four bulk-fill materials and one traditional highly filled nanohybrid composite for posterior use when subjected to a two-body wear rate test and hardness measurement. MethodsFour bulk-fill composites SDR Smart Dentin Replacement (SDR), X-tra base (XBA), FiltekBulk Fill (FUP), Dual-Curing Bulk Composite (FBFL) and conventional nanohybrid resin composite Grandio (GDO) subjected to a two-body wear test against a stainless steel (SS) antagonist wheel. Scanning Electron Microscopy analysis was performed to detect the surface alterations. Microhardness of all samples was tested (n = 5) with a Vickers diamond indenter (5 indentations in each specimen). One-way ANOVA and Tukey’s post hoc test (P < 0.01) were used to analyze differences in wear values. The hardness data were submitted to one-way ANOVA test, followed by the Tukey post hoc test (α = 0.05). T-test was applied to compare wear rate in time interval between one day and one month. ResultsThe highest wear rate values were recorded for SDR and the lowest wear rate values were for GDO. Hardness was the highest for GDO and the lowest for FBFL. SignificanceThe bulk-fill composites have a higher wear rate and lower hardness than the conventional nanohybrid composite, making them less suitable for stress-bearing restorations.

A TRANSITION METHOD FROM DISCRETE SIMULATION TO ELASTIC FEA OF CONTINUOUS MEDIA

A transition method from discrete molecular dynamics (MD) simulation to continuum elastic finite element analysis (FEA) is proposed. Firstly, the moving position and displacement of crystal material atoms is obtained by MD calculation, and then the finite element deformation model under the assumption of continuous medium is constructed according to the characteristics of crystal structure. Further, the strain and stress fields are obtained combined with the constitutive relationship of material mechanical behavior. In order to test the effectiveness of the MD-FEA method, this method is applied to analyze the tensile deformation of Al-Ni soft-hard composite nano cylinder and the nano indentation of substrate Al with spherical diamond indenter. The stress and the strain fields of the above two problems are obtained by MD-FEA method, and the calculated results are compared with the atomic strain calculated by discrete deformation gradient and the atomic potential stress in traditional MD method. The difference between the stress and strain field calculated by MD-FEA method and the traditional MD atomic strain and potential stress is discussed in detail, and the effectiveness of MD-FEA method and its advantages over traditional MD method are discussed. The result shows that the MD-FEA method and the traditional MD method are consistent when the stress and strain change softly in the volume, and in the area where stress and strain change rapidly and in the surface/interface area, the MD-FEA method can calculate the result more precise. Meanwhile, the MD-FEA method avoid the selection of the cutoff radius and weighting functions, which is necessary in traditional MD method and can lead to human error in some circumstances. When the strain is large, there are obvious difference between the small strain calculated by MD-FEA method and the Green strain calculated by traditional MD method. Thus the MD-FEA method is more suitable for the situation that the stress and strain is small.

Plasma nitriding in complex post-processing of stainless steel parts obtained by additive laser technology

Considered are the prospects of applying complex post-processing for an additive manufactured product with the deposition of a multilayer composite coating [Ti0.2C0.8/a-C]40 at the final stage. It is shown that heat treatment, finish milling, ion-plasma nitriding and burnishing with a sliding diamond indenter of a PH1 steel part obtained by selective laser melting (SLM) before deposition of a thin-film coating provides the coating with a minimum surface roughness Ra = 82-86 nm and a maximum hardness of 25.2 ± 1.4 GPa with an increase in the microhardness of the entire “coating-substrate” system.

Influence of mechanical deflector assisted electroless nickel deposits for wear resistance

This investigation reports the effect of mechanical deflector during coating on the mechanical properties of the Electroless Ni-P deposits. Micro hardness of the electroless Ni-P deposits was measured using shimadzu micro hardness measuring unit employing a diamond indenter and pin-on-disc wear tester was used to measure the wear resistance of the deposits. The characteristics of deposits produced in presence of mechanical deflector are found to be superior from those produced using conventional deposition techniques. Enhancement in properties are correlated with modified crystallinity and the conversion of Ni-P in to possible phosphides in the presence of mechanical deflector. It has been noticed that the coating efficiency has 30% hike with mechanical deflector. Annealing at 350ºC has reached the maximum hardness of 950 Hv and subsequent increase in wear resistance.

Room-temperature plasticity and size-dependent mechanical responses in small-scale B1-NbC(001) single-crystals

We report on the mechanical responses of NbC(001) single-crystals subjected to nanoindentation and in situ scanning electron microscopy based uniaxial microcompression tests at room-temperature. Using X-ray diffraction and X-ray photoelectron spectroscopy, we determine that the as-purchased bulk NbC is a 001-oriented, B1-structured, single-crystal with lattice parameter of 0.4446 ± 0.0002 nm and C/Nb ratio of ∼0.99. From nanoindentation experiments performed on the bulk crystal using a Berkovich diamond indenter, we measure an elastic modulus of 495 ± 14 GPa and an indentation-depth (h) dependent hardness decreasing from 31.0 ± 1.2 GPa at h = 0.2 µm to 26.4 ± 0.4 GPa at h = 0.9 µm. During uniaxial compression of cylindrical pillars with top diameters D between ∼0.25 µm and ∼0.75 µm, we observe strain hardening, increasing yield strengths with decreasing D, and surprisingly extensive plastic deformation with strains exceeding 2% and up to 30% in larger-size pillars. Electron microscopy characterization of the compressed pillars reveal slip traces characteristic of {110}〈11¯0〉 and {111}〈11¯0〉 slip systems. We suggest that the unexpected activation of {111}〈11¯0〉 facilitates plasticity in NbC(001).

Effect of different non-invasive and micro-invasive treatment modalities of white spot lesions on microhardness of human enamel

Aim: to investigate effect of different treatment modalities of white spot lesions on microhardness of human enamel. Materials and methods: twenty-four recently extracted sound human maxillary incisor teeth were collected. Teeth were divided at random into six groups (10 each) that were summarized as follows: Group 1: sound unprepared teeth (base line control); Groups 2: demineralized enamel (negative control), Group 3: Demineralized enamel treated by resin infiltration (ICON), Group 4: demineralized enamel treated by bioactive glass (Sylc powder) as remineralizing agent, Group 5: demineralized enamel treated by fluoride varnish ( positive control), Group 6: Demineralized enamel treated by microabrasion. Teeth were embedded in the acrylic blocks with their labial surface flushed with the flat surface of the mold. All specimens except the base line control specimens were demineralized. Each group was treated with the assigned treatment according to manufacturer’s recommendations. The microhardness measurements were performed using a Vickers Microhardness Tester with a Vickers diamond indenter and a 20X objective lens. Results: showed that there was a statistically significant difference in MH values between different study groups (P<0.001). The significantly highest MH mean values were recorded in (microabrasion), (sound enamel), (resin infiltration), and (Sylc powder) groups, which did not differ significantly. This was followed by the mean value of (fluoride varnish) group. While (demineralized enamel) group yielded significantly lowest MH values. Conclusions: among the tested treatment modalities, microabrasion, resin infiltrant as well as bioactive glass air abrasion improved enamel surface microhardness in comparison to fluoride varnish.

A Constitutive Modeling and Experimental Effect of Shock Wave on the Microstructural Sub-strengthening of Granular Copper

Micro-sized copper powder (99.95%; O≤0.3) has been shock-processed with explosives of high detonation velocities of the order of 7.5km/s to observe the structural and microstructural sub-strengthening. Axisymmetric shock-consolidation technique has been used to obtain conglomerates of granular Cu. The technique involves the cylindrical compaction system wherein the explosive-charge is in direct proximity with the powder whereas the other uses indirect shock pressure with die-plunger geometry. Numeric simulations have been performed on with Eulerian code dynamics. The simulated results show a good agreement with the experimental observation of detonation parameters like detonation velocity, pressure, particle velocity and shock pressure in the reactive media. A pin contactor method has been utilized to calculate the detonation pressure experimentally. Wide angled x-ray diffraction studies reveal that the crystalline structure (FCC) of the shocked specimen matches with the un-shocked specimen. Field emissive scanning electron microscopic examination of the compacted specimens show a good sub-structural strengthening and complement the theoretical considerations. Laser diffraction based particle size analyzer also points towards the reduced particle size of the shock-processed specimen under high detonation velocities. Micro-hardness tests conducted under variable loads of 0.1kg, 0.05kg and 0.025kg force with diamond indenter optical micrographs indicate a high order of micro-hardness of the order of 159Hv. Nitrogen pycnometry used for the density measurement of the compacts shows that a compacted density of the order of 99.3% theoretical mean density has been achieved.