Scratch Depth Research Articles

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.

Investigation of Cutting Force and the Material Removal Mechanism in the Ultrasonic Vibration-Assisted Scratching of 2D-SiCf/SiC Composites.

Ultrasonic-assisted grinding (UAG) is widely used in the manufacture of hard and brittle materials. However, the process removal mechanism was never elucidated and its potential is yet to be fully exploited. In this paper, the mechanism of material removal is analyzed by ultrasonic-assisted scratching. Three distinct surfaces (S1, S2, and S3) were selected on the basis of the braided and laminated structure of fiber bundles. The ultrasonic-assisted scratching experiment is carried out under different conditions, and the scratching force (SF) of the tested surface will fluctuate periodically. Under the conditions of different feed speeds, depths, and ultrasonic amplitudes, the normal scratching force (SFn) is greater than the tangential scratching force (SFt), and the average scratching force on the three surfaces is generally S3 > S2 >S1. Among the three processing parameters, the speed has the most significant influence on the scratching force, while the scratching depth has little influence on the scratching force. Under the same conditions and surface cutting mode, the ultrasonic vibration-assisted scratching force is slightly lower than the conventional scratching force. The scratching force decreases first and then increases with the amplitude of ultrasonic vibration. Because the fiber undergoes a brittle fracture in the ultrasonic-assisted scratching process, the matrix is torn, and the surface residues are discharged in time; therefore, the surface roughness is improved.

Molecular Dynamics Simulation of Single-Crystal 4H-SiC Nano Scratching with Different Scratching Directions of the Tool

4H-SiC (silicon carbide) is widely used in semiconductor devices due to its superior characteristics. However, processing techniques such as cutting, grinding, and polishing generally have problems such as low processing efficiency, high cost, difficulties guaranteeing processing quality, and serious material waste. The in-depth research on the mechanical behavior, material removal, and damage mechanism of SiC single crystals at the micro/nano scale is the foundation for solving these problems. This paper establishes a molecular dynamics simulation model for 4H-SiC single-crystal nano scratches, using three different directions of a Berkovich indenter to scratch the surface of the workpiece, studying the surface morphology, scratching force, and material removal during the scratching process. The results indicate that scratching directions of the tool varies, and the surface morphology also varies. After the scratching depth exceeds 1.6 nm, complete dislocations with a Burges vector of 1/3<12¯10> appear on the crystal subsurface, leading to the plastic removal of the material. During the process of material removal, a smaller tool rake angle removes a larger amount of material chips. By analyzing the damage layer of the workpiece, the difference in the damage layer is smaller when the scratching direction is different, but the damage layer generated by the smaller rake angle of the scratching tool is thinner. It shows that the scratching force and workpiece temperature are relatively small when the rake angle of the scratching tool is small. Therefore, when scratching 4H-SiC single crystals, choosing a tool with a smaller rake angle is more beneficial for the process.

Effect of SiC nanowires on adhesion and wear resistance of hydroxyapatite coating on AZ31 magnesium alloy

Hydroxyapatite (HA) coatings doped with different contents of SiC nanowire (SiCnws) were prepared on the surface of AZ31 magnesium alloy by electrophoretic deposition to solve the problems of low adhesion and poor wear resistance of pure HA coatings. Performance tests were conducted on the coating, including corrosion resistance, adhesion and wear performance. The results showed that the prepared coating was intact. The adhesion and wear resistance of the coating were significantly improved when the doping amount of SiCnws was 3%. Among them, the adhesion increased by 37.06% and the scratch depth decreased by 86.67%. At the same time, the corrosion resistance of the coating still maintained a high level. It showed that the performance of doping 3% SiCnws modified coating was balanced and excellent in all aspects.

Drawing fracture behavior and mechanism analysis of ER50-6G welding wire steel

In this paper, we investigated the drawing fracture behavior of ER50-6G welding wire steel and analyzed the factors affecting the fracture, such as continuous casting slag and inclusion, billet structure segregation, Ti inclusion, surface defect inheritance, metallographic structure type, fracture morphology, and so on. OLYMPUS GX53 optical microscope was used to observe and analyze the macrostructure of the cross-section and longitudinal section of the continuous casting billet and the original quality state of the wire rod surface. The continuous cooling transformation curve (CCT curve) of the steel was measured using a DIL805A thermal dilatometer and a Gleeble-3500 thermal simulation test machine. The microstructures of the non-fracture area and drawing fracture of wire rod samples were observed through a ZEISS-ULTRA scanning electron microscope. The results show that the austenite starting transformation temperature (Ac1) and the austenite finishing transformation temperature (Ac3) of ER50-6G welding wire steel are 732 °C and 865 °C, respectively. Under the actual cooling conditions of online production, the strip structure is composed of ferrite (F), pearlite (P), and a small amount of bainite (B). There is a small amount of slag and inclusion in the continuous casting billet; in addition, Al2O3 inclusions and TiC (or Ti(C,N)) inclusions can be observed in the wire rod. The scratch depth of the wire rod surface is 24∼62 μm and the width is 31∼50 μm. With the increase in drawing cumulative deformation, the Al2O3 and TiC (or Ti(C,N)) inclusions that are not easy to deform lead to drawing fracture and brittle fracture. In addition, a small amount of bainite in the wire rod microstructure causes the fracture of the wire with a fine diameter, whereas, the limited-depth scratches on the steel surface do not have an obvious effect on the drawing fracture.

On the formation of pileups during nano-scratching of Inconel 718 produced using additive manufacturing

The objective of this work is to understand the role of microstructure on pileup formation during nano-scratching of additively manufactured nickel superalloy, Inconel 718 (IN718). Scratches with median depths of ∼50 nm were made on as-received and solution annealed IN718 under the action of small normal forces using a spheroconical diamond indenter. The surface profiles of these scratches were then quantified using atomic force microscopy. The as-received IN718 showed a positive correlation between pileup height, and scratch depth. In contrast, the solution annealed IN718 specimen exhibited a negative correlation between pileup height, and scratch depth. Analysis of this observation involved experimental quantification of microstructure using electron back scatter diffraction, quantitative atomic force microscopy, in addition to complementary finite element simulations. Following analysis, we propose that this switchover originates due to differences in strength, hardening, and deformation localization characteristics of as-received and solution annealed IN718.

Influence of Heat Treatment Parameters of Austempered Ductile Iron on the Microstructure, Corrosion and Tribological Properties.

The influence of heat treatment parameters such as the annealing time and austempering temperature on the microstructure, tribological properties and corrosion resistance of ductile iron have been investigated. It has been revealed that the scratch depth of cast iron samples increases with the extension of the isothermal annealing time (from 30 to 120 min) and the austempering temperature (from 280 °C to 430 °C), while the hardness value decreases. A low value of the scratch depth and a high hardness at low values of the austempering temperature and short isothermal annealing time is related to the presence of martensite. Moreover, the presence of a martensite phase has a beneficial influence on the corrosion resistance of austempered ductile iron.

Coating Condition Detection and Assessment on the Steel Girder of a Bridge through Hyperspectral Imaging

The organic coating of bridge steel girders is subjected to physical scratches, corrosion, and aging in natural weathering. The breakdown of the coating may cause serviceability and safety problems if left unnoticed. Conventional coating inspection is time-consuming and lacks information about the coating’s chemical integrity. A hyperspectral imaging method is proposed to detect the condition of steel coatings based on coating-responsive features in reflectance spectra. A field test was conducted on the real-world bridge, which shows obvious signs of degradation. The hyperspectral signature enables an assessment of the coating’s health and defect severity. The results indicated that the coating scratch can be effectively located in the domain of a hyperspectral image and the scratch depth can be determined by mapping a scratch depth indicator (SDI = R532 nm/R641 nm). Rust sources and products in steel girders can be identified by the unique spectral signatures in the VNIR range, and the rust stains (and thus stain areas) scattered on the coating can be pinpointed at pixel level by the chloride rust (CR) indicators >1.11 (CR = R733 nm/R841 nm). The chemical integrity of a topcoat is demonstrated by the short-wave infrared spectroscopy and the topcoat degradation can be evaluated by the decreased absorption at 8000 cm−1 and 5850 cm−1. Hyperspectral imaging enables faster and more reliable coating condition detection by the spectral features and provides an alternative for multi-object coating detection.

Sealing characteristics of aramid fiber reinforced rubber gasket with scratch depth and width defects

AbstractNon‐asbestos gaskets have high tensile properties, good permeability resistance, and resilience. Compared with traditional asbestos gaskets, non‐asbestos gaskets have the advantages of less pollution and no harm to human body. This manuscript presented an experimental and theoretical study of aramid fiber reinforced non‐asbestos gaskets. The tensile strength of gaskets with different fiber orientations and tensile rate were conducted in order to meet the industrial standard. The leakage rates of nondestructive non‐asbestos gaskets with different sizes under different medium pressures and pretightening load were investigated. The results showed that the leakage rate can reach the industrial standard when the pretightening load reached 30 MPa and medium pressures was less than 2 MPa. The artificial scratch defects were made on non‐asbestos gaskets, and the effect of the width and depth of the scratch defect on leakage rate was further investigated. The sealing failure would occur when the scratch depth reached 0.1 mm. The modified model containing defect factors was established. The results showed that the modified model can well characterize leakage rate of gasket.

Erosion-inhibiting potential of the stannous fluoride-enriched CPP-ACP complex in vitro

Currently available anti-erosive agents only provide partial protection, emphasizing the need to enhance their performance. By characterizing erosive enamel wear at the nanoscale, the aim of this in vitro study was to assess the anti-erosive effects of SnF2 and CPP-ACP both individually and synergistically. Erosion depths were assessed longitudinally on 40 polished human enamel specimens after 1, 5, and 10 erosion cycles. Each cycle comprised one-min erosion in citric acid (pH 3.0) and one-min treatment in whole saliva (control group) or a slurry of one of the three anti-erosive pastes (10% CPP-ACP; 0.45% SnF2 (1100 ppm F); or SnF2/CPP-ACP (10% CPP-ACP + 0.45% SnF2)) (n = 10 per group). Scratch depths were assessed longitudinally in separate experiments using a similar protocol after 1, 5, and 10 cycles. Compared with the control groups, all slurries reduced erosion depths after 1 cycle (p ≤ 0.004) and scratch depths after 5 cycles (p ≤ 0.012). The order of anti-erosive potential was SnF2/CPP-ACP > SnF2 > CPP-ACP > control for erosion depth analysis, and SnF2/CPP-ACP > (SnF2 = CPP-ACP) > control for scratch depth analysis. These data provide ‘proof of concept’ evidence that SnF2/CPP-ACP has superior anti-erosive potential compared to SnF2 or CPP-ACP alone.

Investigation of the tribological behavior of the additively manufactured TiC-based cermets by scratch testing

This study deals with the tribological behavior of the TiC-430 L SS cermets fabricated via an additive manufacturing process such as laser powder bed fusion/selective laser melting. A gradient microstructure (finer and coarser morphology) can be observed in the fabricated parts due to SLM's complex thermal history. Using Rockwell indenter, single and multiple passes scratch tests have been performed as a function of applied load to study the wear mechanism of the binder and matrix phase. A surface 3D profilometer was used to analyze the scratch track variation in terms of scratch width and depth. Scanning Electron microscopy (SEM) analysis was performed on the scratched cermet parts to study the wear mechanism and microstructural analysis. It has been observed that the scratch hardness increases with increasing load and the same decreases with increasing the number of passes. Similarly, the coefficient of friction increases with increasing load. Cermets with complex microstructural features exhibit high wear resistance under low loads and for higher loads, multiple passes can lead to tribolayer formation.

Low cycle fretting and fretting corrosion properties of low carbon CoCrMo and additively manufactured CoCrMoW alloys for dental and orthopedic applications.

Additive manufacturing (AM) of CoCrMo metallic implants is growing in the orthopedic and dental fields. This is due to the traditional alloy's excellent corrosion resistance and mechanical properties. AM processes like selective laser melting (SLM) require less time, materials, and waste than casting or subtractive manufacturing complex-geometry structures (bridges, partial dentures, etc.). The objective of this work was to investigate the low cycle tribological and tribocorrosion characteristics of AM CoCrMoW alloys compared to wrought LC CoCrMo (ASTM F-1537) to assess this AM alloy's performance. Fretting and tribocorrosion testing was performed in air (wear only), PBS (wear + corrosion), and PBS with 10 mM H2 O2 (wear + corrosion + inflammation) by a single diamond asperity. No variation between alloys in volume of material removed (p = .12), volume of plastic deformation (p = .13), and scratch depth (p = .84) showed that AM was substantially similar in wear resistance to LC in air and PBS. AM exhibited significantly higher fretting currents (p < .01) at loads up to 100 mN ( = 57 nA and = 49 nA) than LC CoCrMo ( = 30 nA) and ( = 29 nA). In PBS, wear track depth linearly correlates to fretting current, averaged over 100 cycles. Additionally, fretting currents of both alloys were significantly lower in simulated inflammatory conditions compared to PBS alone. AM alloy has generally similar wear and tribocorrosion resistance to wrought LC CoCrMo and would be ideal for patient specific dentistry or orthopedics where precise, complex geometries are required.

Effect of flexible machining on subsurface damage and recrystallization of single crystal superalloy

Single crystal superalloy has gradually become the primary manufacturing material of advanced aero-engine turbine blades. However, it is easy to introduce subsurface damage and recrystallization to worsen the high-temperature service performance during the precision machining process. To investigate the effect of abrasive belt grinding on the subsurface damage and recrystallization of single crystal superalloy, a flexible adaptive continuous feed analysis model was established, which was confirmed by a series of flexible and rigid scratching experiments. The experimental results showed that the plastic deformation area generated by flexible scratch was smaller, but the slip area was larger. The recrystallization depth of flexible scratch was about 35 % lower than that of rigid scratch. The effective material removal rate of the flexible scratch was larger. The flexible reciprocating scratch verified the feasibility of the adaptive continuous feed model. And the recrystallization depth of flexible reciprocating scratch was about 47 % lower than that of rigid scratch. It indicates that the flexible machining method can not only reduce the recrystallization depth but also ensure material processing efficiency. It is expected to provide a theoretical basis and technical support for the high efficiency and low-damage machining of single crystal superalloy.

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.

Multiple Scratching: An Atomistic Study

Using molecular dynamics simulation, we investigate multiple scratching processes in which a tip moves through a groove that has already been formed during a previous scratch. We use a conical indenter such that the friction coefficient is independent of the scratch depth. First, a single scratch to a depth of 4 nm is compared with a 2-cycle scratch in which a scratch at depth 2 nm is followed by a second scratch to the full depth of 4 nm. We observe that the second cycle shows a smaller friction coefficient as long as the tip moves through the pre-formed groove without touching the front end. In addition, we studied 5 cycles of scratching, in which the scratch depth was increased by 2 nm in each cycle. These results confirm and generalize the findings for the 2-cycle scratch. A constant-load 2-cycle scratch simulation emphasizes that the reduction in transverse load—and, consequently, in the friction coefficient—is caused by the fact that, despite a large normal area supporting the normal load, only a thin area is available to resist the transverse movement of the scratch tip. The work done during scratching is in good approximation proportional to the scratch volume showing that the transverse hardness is approximately constant in all scratch processes investigated here.

On the Uniqueness of Wear Coefficient for Abrasive Wear at Nanoscale

AbstractMaterials wear is often characterized by empirical relations as the physical and chemical interactions at sliding interfaces are not fully understood at any length scale. Recent studies showed that these wear relations do not always hold in particular at the nanoscale. Here we discuss the validity range and limitations of two well-known wear models, i.e., Archard’s and Reye’s ones (which were principally developed for adhesive wear) for an abrasive wear process. Using systematic long-timescale molecular dynamic nanoscratching simulations, we show that, at the nanoscale, the wear coefficient increases by the adhesion strength and scratching depth and eventually saturates to a constant value. The saturation is associated with the transition from atomic attrition wear mode to plasticity-induced wear. This new understanding rationalizes discrepant experimental observations on the validity of Archard’s wear relation at the nanoscale. Furthermore, it confirms that a depth- and adhesion-independent wear coefficient can be obtained when plastic deformation dictates the abrasive wear process.

Investigation of Nanoscale Scratching on Copper with Conical Tools Using Particle-Based Simulation

In this study, a modeling approach based on smooth particle hydrodynamics (SPH) was implemented to simulate the nanoscale scratching process using conical tools with different negative rake angles. The implemented model enables the study of the topography of groove profiles, scratching forces, and the residual plastic strain beneath the groove. An elastoplastic material model was employed for the workpiece, and the tool–workpiece interaction was defined by a contact model adopted from the Hertz theory. An in-house Lagrangian SPH code was implemented to perform nano-scratching simulations. The SPH simulation results were compared with nanoscale scratching experimental data available in the literature. The simulation results revealed that the normal force was more dominant compared to the cutting force, in agreement with experimental results reported for a conical tip tool with a 60° negative rake angle. In addition, the simulated groove profile was in good agreement with the groove profile produced in the aforementioned experiment. The numerical simulations also showed that the normal and cutting forces increased with the increase in the scratching depth and rake angle. Although the cutting and ploughing mechanisms were noticed in nano-scratching, the ploughing mechanism was more dominant for increased negative rake angles. It was also observed that residual plastic strain exists below the groove surface, and that the plastically deformed layer thickness beneath a scratched groove is larger for more negative values of the tool rake angle and higher scratching depths.

Subsurface damage model in single and double scratching of fused silica with a blunt indenter

The subsurface damages (SSDs) generated during abrasive processes greatly impact the service performance and life of the devices or components made from brittle materials. The abrasive processes can be simplified as multi-scratching where the abrasive grits tend to be blunt. Consequently, the evaluation of SSDs in the scratching with a blunt indenter is worth of study. In this paper, by extending the blunt indenter-related indentation fracture mechanics and deriving the analytic equations for the contact areas between the indenter and the workpiece, a theoretical SSD depth model is first developed for the single and double scratching of brittle materials. The model correlates the depth of subsurface cone, median, and lateral cracks with the indenter nose radius, scratching depth, residual depth, normal load, tangential load, scratch spacing, and workpiece material properties. To validate the model, scratching experiments are carried out on polished fused silica under different scratch spacing, and the effects of scratch spacing on the surface/subsurface morphologies of scratch grooves, scratching load, and friction coefficient are investigated experimentally. The results show that the radial, cone, median, and lateral cracks are coexistent in fused silica. The second scratching leads to an increase in the fracture degree of the first one, while the SSD depth in double scratching approximates that in single scratching. A small scratch spacing leads to an increase in tangential load or friction coefficient while a decrease in normal load. It is proven that the theoretical model can accurately determine the upper/lower bounds of scratching normal load and subsurface crack depth considering the workpiece fracture degree. Moreover, it is revealed that the SSD depth increases slightly with an increased friction coefficient. This research contributes to the evaluation of SSDs in the abrasive-processed fused silica or similar brittle materials.

Imaging Analysis of Scratch Reduction in Poly (Methyl Methacrylate) (PMMA) Plastic with NOVUS Polishing Products

ABSTRACT Remediation of disfiguring scratches and abrasions on aging plastics challenges even the most experienced conservator. This study assesses the effect of three NOVUS polishing products on remediation of poly (methyl methacrylate) (PMMA). Samples were prepared to mimic the depth and type of scratches observed during conservation treatment performed on vacuum-formed reliefs from the 1960s. The study compares samples of new/unaged PMMA to naturally aged PMMA samples. Two different methods were successfully used to assess the polishing efficacy, which is notoriously challenging to document in transparent and reflective media: (1) image segmentation analysis of photographs to yield scratched area fractions, using three approaches (Li-thresholding, random forest, and convolution neural network); and (2) optical profilometry measurements, which provide surface root-mean-square roughness (RRMS) values. Both methods support the qualitative observations that polishing with the abrasive NOVUS products significantly reduced the surface damage; scratch area fractions decreased from 50–60% to 1–5% across the aged PMMA types after treatment, corresponding to an ∼85% decrease in surface roughness. Critically, the two methods are complementary: the image segmentation results demonstrated a greater visible difference between two degrees of polishing treatments on the new material, while profilometry results were able to parse differences in the degree of scratch reduction between the aged and new materials.

Study on scratch behavior and application of a novel cardanol-based additive in polypropylene

We demonstrated an innovative strategy to synthesize a biobased multifunctional anti-scratch agent (BCP) based on biomass cardanol, and its properties impact for polypropylene (PP) was investigated. The scratch behavior analyses show that incorporation of BCP tremendously ameliorates scratch visibility, greatly decreases scratch depth, color difference and kinetic friction coefficient for PP, which owing to the lubricating layer induced by BCP migration onto the polymer surface. Meanwhile, the addition of BCP greatly increases the initial thermal decomposition temperature of PP and improves the impact strength, mainly benefitting from BCP intramolecular synergism. Furthermore, the constituting concept of novel green BEP enriches the design of polymer additives, with potential expansion into other biomass functionalization with multifunctional variations.