Scratch Speed Research Articles

Experimental study of key factors on super smooth surface fabrication upon single crystal silicon based on mechanochemical synergy

Due to rapid advancements in fields of modern optics and opto-electronics, the need for the production of super-smooth surfaces on single crystal silicon has become increasingly pressing. Although previous research has elucidated the mechanism of material removal and defect evolution in chemical mechanical polishing, brittle characteristic of the vulnerable silicon material makes it rather challenging to catch up with the extreme requirements of high performance and highly efficient manufacture. Nevertheless the critical polishing pressure for scratch free super-smooth surface in pragmatic machining remains undiscovered, which greatly hinders improvement in related fields. Consequently, this paper presents a series of analyses and experiments focused on the material removal process at the micro scale. A micron-sized SiO2 ball tip is utilized to simulate the scratching on surface of a single crystal silicon substrate. Experimental results reveal that appropriate pH conditions and a maximal contact pressure of 0.97 GPa (at a scratching speed of 2 µm/s) between the particle and substrate are crucial for achieving a super-smooth surface. Based on these findings, a defect-free chemical mechanical polishing method is proposed, which involves controlling contact pressure for practical fabrication. Further verification using the KDOSP 650γ machining system and ion beam figuring has demonstrated that a defect-free surface with a roughness of 0.209 nm RMS (Root Mean Square) can be achieved at an average removal rate of 316 nm/min. These insights provide new understandings in the fabrication of super-smooth surfaces on single crystal silicon, offering significant benefits for enhancing the performance of brittle single crystal silicon-based devices and the corresponding machining capabilities.

Resolving high-strain-rate scratch behavior of Ti6Al4V in experiment and meshless simulation

The outstanding strength-to-weight ratio and corrosion resistance of titanium have made it the material of choice in the aerospace industry and medicine. The alpha–beta alloy Ti6Al4V is particularly preferred for its excellent mechanical and bio-compatible properties. Despite its advantages, the low thermal conductivity and poor tribological performance of titanium pose significant challenges during manufacturing and in operation. This research offers deep insights into the high strain rate behavior of Ti6Al4V under abrasive load, such as e.g. experienced in machining, by modifying the standard scratch test setup and using optimized Johnson–Cook material parameters to perform Material Point Method (MPM) simulations. The MPM simulations provide accurate predictions of the data gathered through high strain rate scratch experiments. We found an increase in the von Mises stress distribution as well as the normal and tangential forces required to perform a scratch of the same depth as the strain rate increases. The morphology of the scratch profiles also showed an increase in the height of the ridges that form as the scratching speed increases. These findings are in line with the increase in yield strength and work hardening with growing strain rate. This study bridges the gap between simulation models and experimental observations by providing insights for improved machining strategies and surface treatments that can enhance the performance of Ti6Al4V in demanding applications.

Study on the forming mechanism and evolutionary pattern of stagnant region in mechanical scratching

In this paper, a combination of theoretical modeling, finite element simulation, and experimental methods is employed to investigate the forming mechanism and evolutionary pattern of the stagnant region during mechanical scratching with a diamond wedge tool. The study is structured as follows: Firstly, a theoretical calculation model for the geometric parameters of the stagnant region on the formed groove surface is established based on the contact friction partition mechanism and slip-line field theory. The model indicates that the geometric parameters lB-sg, lV-sg, and ∆lsg of the stagnant region are determined by the length of the stagnant region lp-sg in the plastic flow plane and the transformation parameters. Secondly, the formation process of the stagnant region in mechanical scratching is investigated using an orthogonal cutting simulation model with a negative rake angle tool. The results reveal that the stagnant region is a plastic deformation region formed due to the geometrical characteristics of the negative front surface of the scratching tool and its excessive extrusion, which leads to the formation of adhesive friction within the material. Thirdly, the characteristics of the stagnant region are determined through scratching experiments. Compared to the material in the plastic flow region, the material within the stagnant region exhibits finer and denser microstructures, reduced surface hardening peaks and hardened layer depths, and significantly improved surface roughness. Finally, the evolutionary pattern of the stagnant region under the influence of scratching processing parameters is examined based on the theoretical calculation model of the geometric parameters and the scratching experiment. The findings indicate that as the wedge angle of the scratching tool decreases, the relief angle increases, the absolute value of the rotation angle around the Y-axis decreases, the scratching speed decreases, and the material’s plastic adherence improves, the PI/k value decreases, the lp-sg value increases, and consequently, the geometric parameters lB-sg, lV-sg, and ∆lsg of the stagnant region on the formed groove surface also increase. The deviation analysis of the geometric parameters of the stagnant region reveals a consistent trend between the theoretical and experimental values of lV-sg and ∆lsg, with maximum deviations of 15 μm and 4.13%, respectively. This study provides theoretical and experimental evidence for the establishment of the theoretical model of the stagnant region in mechanical scratching, the analysis of its forming mechanism, and the control of the stagnant region geometric parameters on the formed groove surface.

The effects of the angle between the indenter edge and the scratch direction on the scratch characteristics of Ti–6Al–4V alloy

Ti–6Al–4V alloy has become a crucial raw material in aerospace and other industries owing to its exceptional mechanical properties. However, it is also a typical difficult-to-machine material, and its removal process and mechanism have been widely investigated by scratch testing. Nevertheless, the inherent non-rotational symmetry of the Vickers indenter introduces a crucial parameter, i.e., the angle λ between the indenter edge and the scratch direction, which affects not only the mechanical response of materials but also its surface formation mechanism during scratch. This study systematically characterized the micro/nano scratch characteristics of Ti–6Al–4V alloy under three typical angles λ (0°, 22.5°, 45°) as well as various normal forces and scratch speeds. The coefficient of friction (COF), scratch depth, scratch width, residual scratch morphology, and specific scratch energy were comparatively analyzed. Finite element simulations confirmed that the direction of material flow changed with the change in angle λ. The corresponding deformation mechanisms during scratch were discussed accordingly. The results revealed a significant influence of the angle λ on the scratch behaviors and surface quality of Ti–6Al–4V alloy.

Effects of ferrite and graphite phases on scratch characteristics of nodular cast iron

In this work, we conduct micro-scratch tests of nodular cast iron with Vickers indenter under constant normal load and investigate the effects of individual phases (i.e., ferrite and graphite phases) on the scratch characteristics of nodular cast iron. Using a bimodal Gaussian model to fit the experimental data of penetration depth, residual depth, elastic recovery rate, and scratch hardness, we calculate the contribution percentages of individual phases to scratch variables. The scratch variables are independent of the scratch speed used in this work, while the penetration depth increases linearly with increasing the normal load. There exists a large difference between the contribution percentages and the volume fractions calculated from SEM images and XRD pattern. Such a large difference suggests that the bimodal Gaussian distribution analysis does not include the effect of the interaction between two phases on the scratch characteristics of dual-phase materials with significantly distinct mechanical properties and geometrical dimensions. A more refined method taking into account the interaction between two phases needs to be developed for the analysis of the scratch characteristics of dual-phase materials.

Study of the inhibition mechanism of sapphire subsurface damage by tangential ultrasonic vibration

Ultrasonic vibration has a certain effect on the crack propagation tendency during sapphire grinding, but the mechanism of the effect on the crack propagation tendency has not yet been elucidated. In this study, tangential ultrasonic vibratory scratching and normal scratching sapphire processes were simulated using the discrete element method, and the expansion tendency of sub-surface cracks in the scratching sapphire process was analyzed in terms of cutting forces and stresses. The results of the study show that the crack depth decreases with increasing scratch speed and increases with increasing scratch depth; The greater the variation in cutting force, the greater the number of cracks formed and the crack propagation is mainly distributed near the maximum residual tensile stress; The introduction of tangential ultrasonic vibration induces a decrease in residual tensile stresses and an increase in residual compressive stresses, thus inhibiting subsurface crack propagation; The suppression of subsurface cracks becomes more pronounced as the amplitude increases. Finally, tangential ultrasonic vibratory scratching and normal scratching sapphire experiments were comparatively studied and the experimental results were in agreement with the simulation results. This study provides some theoretical guidance for the suppression of subsurface cracks in sapphire materials during the grinding process.

Understanding the effect of solid lubricants on scratch behavior in epoxy resins: An experimental and statistical approach

AbstractEpoxy resins inherently have low resistance to scratching. To increase the scratch resistance of epoxy resins, reinforcing solid lubricants into the resin is an option. For this purpose, in this study, polytetrafluoroethylene (PTFE) and graphite were reinforced in two different epoxy resins (rigid and toughened) at different reinforcement ratios (5, 10, and 15 wt%). The effects of solid lubricant reinforcement on the scratch behavior of rigid and toughened epoxy resins were examined both experimentally and statistically. Scratch tests were performed throughout a distance of 10 mm using a test apparatus under a load of 15 N and a scratch speed of 30 mm/min. Following the scratch tests, the COF (Coefficient of Friction) values, scratch hardness, scratch width, and depth of all samples were determined and compared to neat epoxy for each resin. In general, it has been determined that solid lubricant reinforcement at higher reinforcement ratios has a positive effect on the COF value (15 wt%). In the case of 15 wt% graphite reinforced rigid and toughened epoxy, a decrease of 15.90% and 17.77%, respectively, was obtained in the COF value compared to the neat epoxy. After the scratch tests, statistical analysis was performed according to RSM to support the experimental results, and ANOVA tables were obtained.Highlights Epoxy adhesives exhibit low scratch resistance. Examining the impact of PTFE and graphite reinforcement on scratch behavior. Two types of epoxy and varied reinforcement ratios (5, 10, and 15 wt%) were studied. Solid lubricant reinforcement to epoxy positively affected scratch behavior.

Polytypic transformation behavior from 4H-SiC to 3C-SiC during high-speed scratching of single crystalline silicon carbide

The phase transformation behavior and associated mechanism of 4H-SiC induced by dynamic processing at room temperature conditions can be investigated with high-speed scratching tests. A dedicated high-speed scratching setup is developed to achieve the speed range over 10 m/s to 30 m/s while microscopic detection is performed to study the microstructural alteration of 4H–SiC. Raman spectra analyses indicate that the polytypic transformation from 4H to 3C occurs during high-speed scratching of single crystalline silicon carbide. Transmission electron microscopy demonstrates a shift in the stacking order of the atomic layers to face-centered cubic at the subsurface of the scratched groove, which reveals the formation mechanism of 3C-SiC. Furthermore, the 4H to 3C polytypic transformation exhibits a sensitive scratching speed correlation. The research can enhance the fundamental understanding of the mechanisms of damage formation during manufacturing of 4H-SiC components and provide g guidance for high-quality processing of 4H-SiC crystals.

Advancements in Polymer Friction and Wear: A Scratch-Modeling Approach

Due to its many applications, including assessing strength, fracture toughness, and so on, the scratch method has attracted much attention in the research community. Finding the tribological characteristics of polymers, such as friction and wear, proved difficult for scratch approaches. This study tested a constant loading scratch method with a Rockwell indenter on the polymeric surface to develop an accessible wear and friction calculation model. Scratch load, speed, and passes, three primary factors, are considered to observe the polymers' response, particularly in terms of width, penetration depth, residual depth, and percentage of recovery. Considering all these scratch parameters, the experiments were conducted on five polymers: polytetrafluoroethylene (PTFE), polyether ether ketone (PEEK), polypropylene (PP), high-density polyethylene (HDPE), and polymethylmethacrylate (PMMA). The scratch characteristics are considered to calculate the friction coefficient and wear throughout the scratching process. Increased groove width, penetration depth, and residual depth and a decrease in recovery percentage are the effects of the number of scratch passes. The strain hardening caused by the multiple movements of the indenter on the same grooves causes a behavior change. With an increase in the scratch pass, the coefficient of friction decreases and stabilizes, and the volumetric wear increases, suggesting that more scratch passes will cause more material loss. This study derived two distinct models by applying the least-square curve fitting technique to evaluate friction and material wear characteristics. This model demonstrates a high degree of compatibility with the specific characteristics of polymeric materials and exhibits a significantly low margin of error.

EFFECT OF CRYSTALLOGRAPHIC ORIENTATION ON MATERIAL REMOVAL BEHAVIOR DURING HIGH SPEED SCRATCHING OF MONOCRYSTALLINE SILICON

Monocrystalline silicon has anisotropic attributes due to asymmetric and non-uniform interatomic lattice structures, which affects its deformation and fracture properties. This paper aims to investigate the effect of crystallographic orientation on the material deformation and removal behavior during high speed scratching of monocrystalline silicon. A high-speed scratching setup is developed which can achieve the highest scratching speed of 40 m/s. Inclined scratching experiments are conducted on (001), (110) and (111) crystallographic planes over the speed range of 1 m/s to 30 m/s. As the scratching depth increases, the ductile-to-brittle transition of silicon at different crystallographic orientations are analyzed. The experimental results suggest that scratching in the direction of "[" ¯("1" ) "10]" on (111) plane presents the largest critical residual depth of ductile-to-brittle transition. Phase transformation from Si-I to the phases of Si-IV and a-Si dominates ductile deformation of silicon during scratching process, while scratching tests in "[" ¯("1" ) "10]" direction on (111) plane demonstrates the largest degree of material amorphization. This study can provide guidance for optimizing processing parameters of monocrystalline silicon components with different crystallographic orientations.

Cutting speed dependence of material removal mechanism for monocrystal silicon

In advanced semiconductor packaging, silicon wafers are typically thinned to tens of microns in thickness using ultra-precision grinding techniques, and the cutting speed greatly determines their surface integrity. However, an in-depth understanding of fundamental material removal mechanism considering the strain rate effect has not been revealed yet. This paper systematically explores the impact of cutting speed on the penetration depth, subsurface damage characteristics and scratch-induced stress field for monocrystal silicon material. First, nanoscratch tests in varied-load and constant-load modes are performed under different scratch speeds on the silicon specimen surface. The surface morphology of generated groove is observed to identify its brittle and plastic features. Next, the geometric relationship and contact pressure between the indenter and workpiece during the scratching process are analyzed. A theoretical penetration depth model is developed considering scratch speed, indenter tip radius and elastic recovery. The corresponding parameters are solved via the particle swarm optimization algorithm and agree very well with the experimental data. Then, the subsurface damage under different scratch speeds is measured by a transmission electron microscope. The atomic scale lattice defects are presented, involving the amorphous layer, stacking faults and phase transformation. Finally, a scratch-induced stress field model is established to interpret the distortion degree variation in damaged regions with scratch speed. The distribution of stress components in the scratch region is presented.

The effects of scratching speed in ultrasonic vibration-assisted single diamond scratching process

Ultrasonic vibration-assisted machining has been widely used in manufacturing hard and brittle materials. Previous studies have shown that the vertical ultrasonic vibration in ultrasound-assisted single diamond scratching can affect the scratching forces, surface quality, and material removal mechanism by two mechanisms: changing the contact mode between the single diamond and the workpiece and increasing the speed of the single diamond relative to the workpiece. However, some studies point out that increasing the speed has little effect on the scratching force and material removal mechanism. Therefore, it is necessary to conduct an investigation that takes into account the effects of both scratching velocity and ultrasonic vibration on scratching force, surface quality, and material removal mechanisms. In this study, the single diamond conventional scratching (CS) and ultrasonic vibration-assisted scratching (UAS) experiments have been conducted at different scratching speeds to investigate the material removal mechanism of ultrasonic vibration-assisted machining. The effects of increasing the scratching speed on cutting forces, material removal mechanism, and machined surface quality are investigated. The results show that in both CS and UAS processes with low to medium scratching speeds (less than1000 mm/s), increasing the scratching speed leads to more brittle material removal and lower surface quality. At the same time, the scratching speed has almost no effect on the scratching speed force.

Strain rate effect on material deformation and removal behavior during high speed scratching of 4H‐SiC

The effects of strain rate on material deformation and tribology behavior of 4H‐SiC are studied with high speed scratching tests, which represent typical processing modes of SiC wafers such as abrasive grinding/polishing. The results show that higher scratching speeds tend to induce more surface defects at the same scratching depth, which leads to the occurrence of ductile-to-brittle transition at smaller scratching depths. The relationship between the strain rate and scratching stress is analyzed, based on which a novel material model of 4H‐SiC is proposed considering the strain rate effect. The research reflects a close correlation between scratching speed-dependent stain rate and material deformation behavior of 4H‐SiC, and it can provide guidance for process optimization during manufacturing of 4H‐SiC components.

Influence of tool vibration and cutting speeds on removal mechanism of SiCp/Al composites during ultrasonic elliptical vibration-assisted turning

Revealing the mechanical removal mechanism and improving the machinability of SiCp/Al composites is always demanding because of the diversity of mechanical properties between the plastic matrix and brittle reinforcement. As an effective processing method, ultrasonic elliptical vibration-assisted turning (UEVT) has been proven to enhance the machinability of difficult-to-machining material, but the impact of vibration effects on deformation behavior of SiCp/Al composites has not been accurately studied. This paper investigates the mechanical removal mechanism of SiCp/Al composites in UEVT compared with traditional cutting (TC), evaluates the influence of tool vibration and removal speeds on particle deformation by scratching tests. Different from TC, high-density zone of broken particles dominates the surface morphology with low cutting speed in UEVT, which is conducive to reducing surface roughness. UEVT technology is beneficial to interrupt the continuous impact of particles on rake face, obtaining lower interface temperature and slighter tool wear. In addition, it is observed that the cluster stripping of Al matrix appears in removing of SiCp/Al composites by TC with high scratching speed, which has negatively influence on surface roughness and cutting edge integrity. Finally, a rational selection of cutting speed (200 mm/min) and UEVT technology are beneficial for the outstanding machinability of SiCp/Al composites. The interesting discoveries provide a significant theoretical basis and practical machining guidance for process optimization of cutting parameters to improving the machinability of SiCp/Al composites in UEVT.

Investigation of the influence of cooling lubricants on workpiece topography

AbstractModel‐based prediction is becoming increasingly important to meet the ever‐increasing demands on manufacturing. In grinding, the prediction of the process forces and the generated surface by physical models are particularly important.Since cooling lubricants are almost always used on an industrial scale, the grinding model, developed at our institut, must be extended to include this component. Therefore, in order to implement cooling lubricants into the FEM‐based model, it is first necessary to investigate the behaviors and effects of cooling lubricants in real experiments. Various influencing factors such as the scratching speed of individual abrasive grains in interaction with cooling lubricants need to be investigated. However, the existing physical grinding model is not limited exclusively to the prediction of the resulting forces. It is also supposed to be able to qualitatively predict the expected resulting surface of the workpiece. Hence, this paper will focus on the topographic characteristics that can occur in the scratch test due to different cooling lubricants and scratching speeds.Based on real experiments on a test rig for such scratch tests, it has been shown that different scratch speeds have a negligible influence on the topographical nature and expression of a scratch. In contrast, however, there is a direct influence of cooling lubricants on the topographic properties. This effect is additionally influenced by the viscosity of the cooling lubricant used.

Interfacial and Tribological Characteristics of MoS2 on Ni Under Nanoindentation and Nanoscratch

With the rapid development of science and technology, microscale machining has become an important topic, and lubricants play a vital role in machining. Solid lubricants are suitable for a variety of precision machining better than liquid lubricants. Molybdenum disulfide (MoS2) in 2D‐layered nanomaterials is a promising candidate for use as a solid lubricant. Herein, molecular dynamics (MD) simulations are performed to study the effects of scratch depth, speed, and temperature on the mechanical properties of Ni‐based MoS2 thin films. The results show that atom stacking and extrusion around the abrasive tip increase the friction coefficient in the indentation and scratch phases. The higher value of scratch depths, speeds, and temperatures can lead to higher friction coefficients and wider dislocation distributions. Moreover, Shockley dislocation appears in all cases at all effects, and the total dislocation length increases with the higher value of scratch depths, speeds, and temperatures.

Surface and subsurface formation mechanism of SiCp/Al composites under ultrasonic scratching

Rotary ultrasonic machining (RUM) is an effective method of high-quality and high-efficiency machining for advanced composites. However, the machining mechanism and kinematic characteristics of ultrasonic machining of SiC particles-reinforced aluminum matrix (SiC p /Al) composites are yet unclear, limiting the applications of RUM in composites machining. In this study, a rotary ultrasonic vibration-assisted scratch (RUVAS) test was designed for the high-volume fraction of SiC p /Al composites. The kinematic and scratch force model of RUVAS was developed to describe the scratch process of SiC p /Al. Both RUVAS and conventional scratch (CS) tests were performed under various scratch speeds on SiC p /Al. The scratch trajectory was divided into three modes: continuous, semi-continuous, and intermittent. We observed the formation of different surface morphology under different modes. The scratch force difference between RUVAS and CS was insignificant when the scratch speed is high, which indicated that the effect of ultrasonic vibration diminished at a high speed when the ultrasonic frequency was fixed. When assisted by ultrasonic vibration, the scratch morphology of SiC p /Al indicated that the matrix has undergone significant plastic deformation. While the hard SiC particles tended to be ruptured and pressed into the plastic matrix, this mechanism can effectively suppress the initiation and propagation of cracks, which is beneficial to reducing the stress influence zone, healing the surface defects, and improving the surface integrity. The subsurface morphology indicates that the subsurface damage under CS and RUVAS mainly includes particle cracking, matrix tearing, and interface failure. Our experimental result shows that ultrasonic vibration can effectively reduce the subsurface damage of SiC p /Al composites, bringing insight into fundamental mechanisms of ultrasonic machining and providing guidance for the vibration-assisted processing of SiC p /Al composites.

Characterization of graphene reinforced 3C-SiC composite as a metal-free friction material using molecular dynamics simulation

In this work, the tribological, mechanical and thermal properties of graphene (Gr)-based 3C-SiC nanocomposite as a metal-free friction material were first studied by using molecular dynamics (MD) simulations. In tribological properties, the frictional force, normal force, effective coefficient of friction and wear rate were investigated. The effects of scratching depth, temperature, scratching velocity and the number of Gr layers in the composite to the friction process were considered. Young’s modulus, ultimate tensile stress (UTS) and failure strain in the mechanical properties, and thermal conductivity in the thermal property were also included to understand the tribological performances of the composite. The interfacial interaction energy was evaluated to characterize the effect of interface on material properties. The validations were performed on some representative results. In the simulation results with the selected configurations which are listed in the subsequent content, the nanocomposite showed the lowest wear rate with an appreciable coefficient of friction at the scratching depth of 10 Å. 10 m/s was the optimal scratching speed to maintain the best wear performance. A temperature of 300 K yielded the highest coefficient of friction and the lowest wear rate. The model with three Gr layers showed a relatively high coefficient of friction and a relatively low wear rate. The model with five Gr layers stacked in 3C-SiC exhibited the best mechanical performance. The nanowire model with two Gr layers showed a higher thermal conductivity. The research findings will provide guidance in design and manufacturing of Gr/3C-SiC friction materials. The study will also help understand the effect of Gr as a potential reinforcement for metal-free friction materials.

A Novel Grain-Based DEM Model for Evaluating Surface Integrity in Scratching of RB-SiC Ceramics

A novel grain-based DEM (Discrete Element Method) model is developed and calibrated to simulate RB-SiC (Reaction-Bonded Silicon Carbide) ceramic and associated scratching process by considering the bonded SiC and Si grains and cementitious materials. It is shown that the grain-based DEM model can accurately identify transgranular and intergranular cracks, and ductile and brittle material removal modes. It also shows that by increasing the scratching speed or decreasing the depth of cut, the maximum depth of subsurface damage decreases, because the scratching force is relatively large under the low scratching speed or large depth of cut that facilitates the occurrence of transgranular cracks, large grain spalling from the target surface and the propagation of median cracks into the target subsurface. It has further been found that increasing the cutting-edge radius can enhance the target ductile machinability and reduce the target subsurface damage.

Understanding the surface generation mechanism during micro-scratching of Ti-6Al-4V

A lot of grinding research in the past has been emulated using single grit scratching. This limits studying surface generation mechanism due to overlapping scratches inherent to the grinding process. It not only affects the surface generation mechanism, but also limits studying elastic recovery which has a significant effect on the final form and topography including the roughness generated after grinding. Taking Ti-6Al-4V as a testbed, this investigation was directed on comparing single scratches with adjacent scratches, which are often referred to as double scratches in literature. During the experiments, the effect of scratch speed and the scratch separation distance on the cutting forces, material pile-up area ratio (PA), groove depth, material removal area (MRA), and sub-surface deformation were investigated. It was found that the scratch speed significantly affects the pile-up and groove depth because of phenomena like stress build-up and elastic recovery. A complementary analytical model of ploughing and shearing forces developed here led to the observation that the minimum chip thickness can only be around 0.1 to 0.2 times the radius of the indenter. Elastic recovery was found to be larger at the middle of the scratch, which was confirmed by the stress-strain relations derived from the FEM simulations. It was also observed that the spacing between two subsequent scratches can significantly affect the scratched surface quality. These experiments show that the severe ploughing and mid-region ridge features can be avoided by having the scratch pitch to be at least one third of the grit tip radius.