Scratching Process Research Articles

Mechanical response of ZrxCu100-x layer on Cu(001) substrate using molecular dynamics

The molecular dynamics simulations method is applied to survey the deposition and annealing processes of ZrxCu100-x film on a Cu(001) surface. The influences of ZrxCu100-x compositions and depths on the force, deformation behavior, pile-up, and hardness are investigated using nano scratching and nanoindentation processes. We find out that the structure of ZrxCu100-x alloy has stability increases when decreasing the Zr content. The surface roughness of Zr-Cu film increases when improving the Zr content. After annealing, the morphology surface of the Zr-Cu amorphous alloy becomes smoother. The scratching forces and average friction coefficient of the Zr20Cu80 film surge as the scratching depth rises. While the pile-up height, normal force, and friction force decrease as increasing the Zr ratio. Under the plastic and elastic deformations, shear transformation zones are formed in the Zr-Cu amorphous film. While in the nanoindentation process, the hardness of ZrxCu100-x film amorphous film tends to decrease when increasing the Zr content.

Investigation on diamond damaged process during a single-scratch of single crystal silicon carbide

Through a series of single-scratch experiments, the damaged process of diamond grit and the material removal mechanism of single crystal silicon carbide (SiC) were investigated. The <111> and <110> planes of single diamond grits were used to scratch the carbon (C) face and silicon (Si) face of single crystal SiC, respectively. The damaged process and corresponding typical damaged morphology of diamond grits on different planes were analyzed. The material removal mechanism of single crystal SiC (C face and Si face) is analyzed. The results show that the contact width and the breaking angle were determined as the key damaged parameters of diamond grit by the analysis of the damaged process. However, the key factor to reduce surface damage is the state of the micro-edges that appear on the crystal plane of the diamond grit in contact with the workpiece during the scratching process.

Nucleation and detachment of polystyrene nanoparticles from plowing-induced surface wrinkling

We report the formation of spherical particles (up to 250 nm in diameter) from polystyrene surfaces repeatedly scratched by atomic force microscopy nanotips (nominal radius < 10 nm) along a series of parallel lines. The particles nucleate from the crests of the ripple profiles formed in the beginning of the scratch process. They are subsequently detached and progressively displaced by the tip across the ripples till the edge of the scanned area, where they pile up without coalescing. The detachment occurs smoothly without static friction peaks, suggesting that the particles are torn off as a result of a crazing mechanism induced by the tip when it is pushed against the ripple crests. Considering the negative impact of nanoplastics on the environment and human health, and the absence of established methodologies for a quantitative analysis of these processes at the level of single particles, our results will help to promote systematic characterization of plowing wear on different polymeric materials and different environmental conditions.

Modeling and experimental study of machining outcomes when conducting nanoscratching using dual-tip probe on single-crystal copper

Atomic force microscopy (AFM) tip-based nanomachining technique has been proved as a powerful method to fabricate nanostructures. The nanomachining approach proposed in this study offers a new concept to improve the width resolution and processing efficiency of AFM tip-based nanofabrication techniques. The method uses a dual-tip probe and single-crystal copper is used as the sample material. A depth prediction model is developed for the nanoscratching process using the dual-tip probe. The results obtained by nanoscratching tests show that symmetrical three-dimensional (3D) nanostructures composed of two large pile-ups and one small hump can be machined. The model predicts the machined nanostructure depth accurately when the machined depth reaches approximately 40 nm; the blunt tip and the inclined inner wall of the dual-tip gap may be the main reasons for the inaccurate predictions at smaller machined depths. Moreover, molecular dynamics (MD) simulation is also used to investigate the scratching process with the dual-tip probe. The simulation results obtained agree well with the experimental results.

Experiment and Smooth Particle Hydrodynamics Simulation for the Wear Characteristics of Single Diamond Grit Scratching on Sapphire

Abrasive single crystal diamond (SCD) grit is widely used in the machining process of sapphire. The wear of SCD grit has a significant influence on the surface quality of sapphire. In this paper, smooth particle hydrodynamics (SPH) method is employed to reveal the wear mechanism of SCD grit with Steinberg constitutive equation and Grüneisen state equation. The wear morphology, wear volume and scratching forces are measured and analyzed by combination of SPH simulations and experiments. The results show that the scratching forces fluctuate in a certain range and decrease with the increasing of workpiece material removal volume. Different degrees of cleavage and fracture appear in the front and rear of SCD grit. The shear stress and extrusion stress are the main stresses of SCD grit during the scratching process. The wear progress and wear form are mainly determined by the stress state. Different stress state leads to different wear progress of the SCD grit. The SPH method is able to reflect and illustrate the wear characteristics of SCD grit scratching on sapphire.

Molecular dynamics simulation of monocrystalline copper nano-scratch process under the excitation of ultrasonic vibration

In order to explore the mechanism of unidirectional ultrasonic vibration-assisted machining from a microscopic point of view, the molecular dynamic (MD) simulation method is used to simulate the scratch process of monocrystalline copper under ultrasonic excitation. By comparing the simulation results of traditional scratching and ultrasonic vibration-assisted scratching, the influences of ultrasonic vibration on the surface morphology, the tangential force, and the evolution of the crystal’s internal defects are discussed. The results show that the ultrasonic vibration can improve the surface quality of the workpiece, reduce the tangential force, and reduce the energy consumption. Simultaneously, ultrasonic vibration promotes the interaction between dislocations, accelerates the annihilation of dislocations, effectively reduces work hardening caused by dislocation accumulation, and forms a large number of vacancies and interstitial atoms.

Surface deformation of single crystalline copper on different nano-scratching paths

Anisotropic deformation behavior of single crystalline material under scratching has a significant effect on machining precision in nano-mechanical machining. In the present work, a crystal plasticity finite element model simulating the scratching process is developed, and the established model is validated by comparison with experimental results. (001)-, (101)- and (111)-oriented coppers are selected to investigate the deformation behavior including scratching depth, surface topography and subsurface deformation affected by scratching path. Further, the deformation mechanisms of (001)-, (101)- and (111)-oriented coppers are analyzed to be caused by deformation of slip systems.

Effect of Sample Tilt on Indentation and Scratch Behavior of Single Crystal Copper

Inclined factors bring a lot of errors to indentation and scratch experiments. The aim of this paper is to investigate the effect of sample tilt on indentation and scratch behavior of single crystal copper. Angled indentation and scratching experiments were conducted on the flat of 5°,10°,15° and 30°, and spherical-conical indenter was used to study the effect. In scratching simulation with SPH method, normal and lateral forces during scratching process increased when tilt. Contrary to simulation result, when contact depth was held as a constant, the forces declined as tilt angle increased. In geometry model, the actual indentation depth was less than the theoretical contact depth and the projected area of the tilt indenter was an enclosed area like an elapse with two circular arcs. Residual impression images of indentation and scratching indicated that not only the sphere section of the tip of indenter, but also the conical surface penetrated into sample and squeezed a slope. The results showed that the size of spherical-conical indenter has significant effects on the size and shape of wear debris and could not be neglected during indentation and scratching tests with sample tilt.

Theoretical modeling and experimental analysis of single-grain scratching mechanism of fused quartz glass

Abstract Surface and subsurface damage, including cracks, scratches, microcracks, and residual stress, is inevitable when fabricating fused quartz glass because of their high brittleness and low fracture toughness. Single-grain scratching mechanism of fused quartz glass is examined using smoothed particle hydrodynamics (SPH) to clarify the mechanisms of material removal and produce crack-free optical surfaces. Single diamond grain experiments were conducted to validate the proposed SPH model, which predicts the critical depth of approximately 0.20 μm for ductile–brittle transition in fused quartz glass. Both simulation and experimental results indicate that three removal regimes, namely, complete ductile, ductile–brittle transform, and complete brittle modes, are involved in the material removal process. SPH simulation helps identify the location of crack formation and morphology of crack propagation during scratching. Thus, the SPH model is used to simulate the single grain scratching process under different conditions. Simulation results reflect that changing the scratching speed will lead to a remarkably different mechanism of crack initiation and propagation compared with changing the scratching depth. Effects of scratching depth and speed on scratching force and residual stress are also discussed thoroughly in the simulation analysis.

Damage Mechanisms of Material in Single-Cone Scratching

Abstract The scratching test has been a key method to characterize the basic mechanics of material in vast scenarios. Although attentions have been paid to this field for decades, a comprehensive analytical framework, which includes material flow, fracture initiation, and crack propagation, is still missing. The wide application of scratching test and the accurate description of material behaviors in friction is thus limited. To address the problem, an analytical frame model was established in this study. The strain distribution and pileup ratio in the symmetry section of the front ridge was calculated. Furthermore, the ductile fracture law was also included to predict the mechanism and the initiation location of fracture in the scratching process. The predictive results were further validated by scanning electron microscope (SEM) observations of the scratched grooves. The effects of cone angle and material properties on the damage mechanisms of material in the scratching process were studied. It was revealed that the damage mechanism changes from shear failure to tensile failure, and further to plastic deformation with the increase of cone angle and the ratio of yielding stress to Young’s modulus. Finally, a map of the damage mechanism of material in the scratching process was obtained by utilizing the developed model. The presented works are meaningful to the understanding of material behavior in ploughing and helpful in predicting and controlling the surface quality of those parts subject to different machining and forming processes.

The material removal and the nanometric surface characteristics formation mechanism of TiC/Ni cermet in ultra-precision grinding

In this paper, the material removal mechanism of TiC/Ni cermet is firstly investigated based on the analysis of the nano-indentation and the diamond scratching test, and the grinding induced surface damage mechanics is then explored according to the surface topography, the surface morphology and the material microstructure analysis. The results show that the material removal experienced plastic deformation, plowing and fracture under the dynamic scratching process, where the material microstructure plays a determinant role on the obtained surface characteristics of the TiC/Ni cermet. To achieve a smooth surface and ductile material removal by the ultra-precision grinding process, a group of the machining parameters is selected to reveal the formed nanometric surface characteristics, where the dislodgement of the hard TiC particles and the surface relief formation were induced by the varied material removal rate between the binding phases and the TiC hard particle under the scratching of the diamond grits. In addition, the preferred TiC (200) crystalline plane in the ground surface layer appears for the interface fracture between the TiC grains and the rim structure, while the Ni (111) crystalline plane shows a preferred growth for the extrusion in the subsurface deformed layer.

Towards understanding the machining mechanism of the atomic force microscopy tip-based nanomilling process

Atomic force microscopy (AFM) tip-based nanofabrication is as a powerful method to machine nanostructures. However, the traditional AFM scratching process suffers from low processing efficiency and a low rate of material removal. Thus, an AFM tip-based nanomilling method was previously proposed to improve the machining efficiency and material removal rate; however, the machining mechanism of the nanomilling process, especially on hard-brittle silicon crystals, is not well understood. In this study, we used an AFM tip-based nanomilling approach to machine nanochannels on single-crystal silicon to investigate the machining mechanism (i.e., the material removal state, undeformed chip thickness, the brittle-to-ductile transition, and subsurface damage). For the first time, we established a theoretical model for tip-based nanomilling with a constant normal load to predict the machined depth. Nanochannels fabricated with a wide range of feed directions, crystal orientations, and tip trajectories were obtained, which provided a reference for machining high-quality nanochannels and an in-depth understanding of the nanomilling of single-crystal silicon. The experimental results demonstrated that we could machine a nanochannel without pile-ups by selecting a specific trajectory with a feed smaller than 4 nm in the 0° direction, a normal load no greater than 120 μN, and a crystal orientation at rotation angles of 135°, 157.5°, or 180°. Moreover, transmission electron microscope analysis of the subsurface of the nanochannel revealed a large number of dislocations, stacking faults, and a layer of amorphous silicon. Our findings are of great significance for obtaining high-quality nanochannels with a predicable machined depth and understanding the nanomilling mechanism of hard-brittle materials.

Investigations on thermal effects on scratch behavior of monocrystalline silicon via molecular dynamics simulation

Scratching along monocrystalline silicon [110] crystal orientation at the temperature from 1 K to 1000 K were carried out by molecular dynamics (MD) simulations to study thermal effects on machining performance and subsurface damage mechanisms. Scratch force and phase transformation at different temperatures were studied. The results reveal that high temperatures can induce small scratch force and high material removal rate. Amorphous silicon can always appear beneath the scratched surface, irrespective of temperature. The generation and stability of bct5-Si show high dependence on temperature. At the temperature from 1 K to 500 K, there is bct5-Si generated beneath amorphous silicon during the scratch process, which is not found above 600 K. Bct5-Si beneath amorphous silicon layer keeps stable after scratching at 1 K and 100 K, while is transformed into amorphous silicon at the temperature from 200 K to 500 K.

Characterization of metakaolinite micro-mechanical behaviors using MD simulation

The mechanical behavior of metakaolinite under nanoindentation and nanoscratching was investigated by means of molecular dynamic (MD) simulations in this study. A 6 nm radius spherical indenter was pressed on the (001) and 001¯ basal planes up to a 3.5 nm indentation depth to study the anisotropy of metakaolinite in hardness and Young’s modulus. The higher hardness was found in silica facet as it possessed a hexagonal-close-packed plane that is the most densely packed plane. During scratching, a 3 nm radius spherical indenter was used to scratch the substrate surfaces up to 8 nm length, the scratching behavior in different scratching depth and speed was studied. Both normal and scratch forces increased as the scratching processed, while scratch force showed a high dependence on scratching depth. At high scratching depth of 2.5 nm and 3.5 nm, pile-up of atoms towards the free surface and formation of chip via the shear zone were observed, the chip volume was found to increase with the increase of scratching depth. The metakaolinite appeared to soften slightly, as demonstrated by normal hardness decreased with depth. The depth dependence was more conspicuous on the scratch force than for the normal force, while the scratching speed had little effect on the scratching process.

Microstructures generated in AISI 316L stainless steel by Vickers and Berkovich indentations

Abstract The work aimes for studying the specifics of deformation of AISI 316L stainless austenitic steel under the conditions of micro severe plastic deformation (mSPD) created locally at the submicro and micro levels using Berkovich and Vickers indenters. The deformation was carried out by instrumented (depth-sensing), quasi-static indentation and microscratching methods in the load interval P = 10–2000 mN. Studies have shown that various mSPD methods (submicro-, microindentation and microscratching) create similar patterns of plastic deformation in thin surface layers of the material. The stick-slip nature of the scratching process has been demonstrated. It has been established that in the region of loads below 50 mN, the intragranular deformation mechanism has the main contribution to the formation of indentations, while at loads above 50 mN, intragranular and intergranular mechanisms participate in the process, and the role of the latter becomes greater with P increase. Load growth leads to a decrease in hardness under submicro-, microindentation and microscratching for all applied mSPD methods. The type of mSPD method, as well as the type of indenter and the magnitude of the applied load are the factors affecting the mechanical characteristics that should be taken into account depending on the practical purpose of the AISI 316L austenitic steel products.

A molecular dynamics study on the tribological behavior of molybdenum disulfide with grain boundary defects during scratching processes

The effect of grain boundary (GB) defects on the tribological properties of MoS2 has been investigated by molecular dynamics (MD) simulations. The GB defects-containing MoS2 during scratching process shows a lower critical breaking load than that of indentation process, owing to the combined effect of pushing and interlocking actions between the tip and MoS2 atoms. The wear resistance of MoS2 with GB defects is relevant to the misorientation angle due to the accumulation of long Mo-S bonds around the GBs. Weakening the adhesion strength between the MoS2 and substrate is an efficient way to improve the wear resistance of MoS2 with low-angle GBs.

Study on the subsurface damage mechanism of optical quartz glass during single grain scratching

The single grain scratching SPH simulation model was established to study the subsurface damage of optical quartz glass. Based on the analysis of the stress, strain and scratching force during scratching, the generation and propagation of subsurface cracks were studied by combining with the scratch elastic stress field model. The simulation results show that the cracks generate firstly at the elastic-plastic deformation boundary in front of the grain (φ = 28°) due to the influence of the maximum principal tensile stress. During the scratching process, the median crack closes to form the subsurface damage by extending downward, the lateral crack promotes the brittle removal of the material by extending upward to the free surface, and microcracks remain in the elastic-plastic boundary at the bottom of the scratch after scratching. The depth of subsurface crack and plastic deformation increases with rising scratching depth. The increase of scratching speed leads to the greater dynamic fracture toughness, accompanied by a significant decrease of the maximum depth of subsurface crack and the number of subsurface cracks. The subsurface residual stress is concentrated at the bottom of the scratch, and the residual stress on both sides of the scratch surface would generate and propogate the Hertz crack. When the scratching depth is less than 1.5 μm or the scratching speed is greater than 75 m/s, the residual stress value and the depth of residual stress are relatively small. Finally, the scratching experiment was carried out. The simulation analysis is verified to be correct, as the generation and propagation of the cracks in the scratching experiment are consistent with the simulation analysis and the experimental scratching force indicates the same variation tendency with the simulation scratching force. The research results in this paper could help to restrain the subsurface damage in grinding process.

The Benefit of Superelastic NiTi Addition on Corrosion Performance of Electroless Ni–P Coating During an Accidental Scratch Event

Electroless Ni–P–NiTi composite coatings were prepared on API X100 steel substrates by incorporating Ti particles into Ni–P matrix followed by annealing Ni–P–Ti coatings. The scratch behavior of the as-deposited and annealed coatings under a high load was studied. It was found that the highest scratch resistance is achieved on the annealed 11.8 wt% Ti coating among all the coatings due to the formation of superelastic NiTi particles after annealing. Transformation toughening induced by superelastic NiTi particles significantly improves the toughness and scratch resistance of the annealed 11.8 wt% Ti coating. The effect of scratching on corrosion behavior was also investigated. Potentiodynamic polarization (PP) and electrochemical impedance spectroscopy (EIS) results revealed that the corrosion resistance of pre-scratched annealed Ni–P–Ti coating is higher than both the as-deposited Ni–P and Ni–P–Ti coatings. The highest corrosion resistance is achieved on the pre-scratched annealed 11.8 wt% Ti coating. The addition of NiTi particles into Ni–P matrix prevents crack nucleation and propagation during scratching process, which decreases the available surface area for localized corrosion and improves the corrosion resistance of the annealed 11.8 wt% Ti coating. This research reveals that the corrosion resistance of Ni–P coating is improved by the presence of superelastic NiTi particles within the Ni–P matrix during an accidental scratch event.

Micromechanical performance of high-density polyethylene: Experimental and modeling approaches for HDPE and its alumina-nanocomposites

The scratch resistance of polymers is important for numerous applications, as scratching can lead to degradation of surface properties and also represents an elementary process in abrasive wear. However, scratching of polymers is a complex process involving several modes of deformation, and theoretical understanding of it is incomplete. Numerical modeling is a potentially useful means towards a clearer picture of the scratching process, but the central role of tip-substrate contact and highly localized large deformations makes finite element analysis (FEA) challenging. Here, we take further the numerical approach by investigating a highly ductile semi-crystalline polymer by FEA and taking the inherent rate dependency of polymers into account by using an elasto-viscoplastic material model. Two γ-Al2O3 and f-Al2O3 HDPE nanocomposites, which have shown themselves to be suitable for tribological applications, are studied. We discussed the effect of nanofillers on the scratch behavior and highlight the significance of recovery properties, which still pose a challenge to numerical modeling.

Theoretical modelling of brittle-to-ductile transition load of KDP crystals on (001) plane during nanoindentation and nanoscratch tests

KDP single crystals are widely used in inertial confinement fusion and high power lasers due to the wide transmission band, high laser damage threshold, large nonlinear optical coefficient, etc. However, surface and subsurface damages are easily induced into the KDP crystal components during the machining process due to its high brittleness and distinct anisotropy. These damages will reduce the service accuracy and life of KDP crystal components. It is of great significance to study the brittle-to-ductile transition of KDP crystals to achieve high efficiency and precision machining of crystal components. In this work, a theoretical model of brittle-to-ductile transition load during the nanoindentation and nanoscratch processes of KDP crystals was established based on the energy conservation law and dislocation theory. This model took the anisotropy of KDP crystals into account. Nanoindentation and nanoscratch experiments by using different indenters were performed to verify the theoretical model of brittle-to-ductile transition load. The experimental results of the brittle-to-ductile transition load agreed well with the theoretical results, which indicated that the model was reliable. Both experimental and theoretical results showed that the critical load of brittle-to-ductile transition during the nanoindentation and nanoscratch processes increased as the half cone angle increased. In addition, the critical load of brittle-to-ductile transition load of the scratch was lower than that of the indentation under the same condition. The results also demonstrated that KDP crystals had distinct anisotropy during the nanoindentation and nanoscratch process. Brittle fracture was most likely to occur along [100] orientation during the scratch process. Under the same scratching condition, [110] orientation was prone to achieving ductile machining with high surface quality compared with other orientations.