Scratch Velocity Research Articles

Molecular dynamics study of the scratching property of the tetrahedral amorphous carbon coating on the piston ring

In order to reduce friction and wear of the piston ring-cylinder liner system of the internal combustion engine, the tetrahedral amorphous carbon (ta-C) coating on the piston ring is considered. The scratching properties of the ta-C coating and diamond ball are studied by molecular dynamics simulation. The atomic configuration, surface morphology, RMS roughness, friction force, coefficient of friction, wear rate, and normal stress of the ta-C coating are analysed under different scratching depths, substrate temperatures, and scratching velocities. The interatomic interactions are described using the second nearest-neighbour modified embedded-atom method potential, as well as Tersoff potential and Lennard-Jones potential. The simulation results show that the ta-C coating exhibits excellent scratching properties. The scratching depth has a significant effect on the scratching property of the ta-C coating, while the substrate temperature and scratching velocity have a relatively small effect.

Nano-tribological behavior and structural evolution of 304 stainless-steel by molecular dynamics simulation and experiment

304 stainless-steel has excellent mechanical properties and is commonly used in ultra-precision instrumentation. Nevertheless, the research on the intricate nano tribological behavior of 304 stainless-steel during ultra-precision machining remains limited. In this work, the tribological behavior of 304 stainless-steel is investigated at different indentation depths and scratching velocities by molecular dynamics (MD) simulations and nano-scratch tests. The results show that higher indentation depths lead to more serious damage on the surface and subsurface of 304 stainless-steel. The friction force and friction coefficient also increase significantly with higher indentation depths. It is worth noting that the dislocation density is much smaller at the low-indentation depth, which is due to the large-scale dislocation annihilation at this depth. As the scratch velocity increases, the subsurface shear stress decreases, the dislocation length rises, and it is accompanied by the generation of V-shaped dislocations, which are caused by dislocation entanglement within the substrate. In addition, nano-scratch tests were performed and similar trends were obtained by comparing the results with simulations. This work provides theoretical guidance for a deeper understanding of the deformation behavior of 304 stainless-steel during nano-scratching and its engineering applications at the micron and nano-meter scales.

Atomic insight into tribological behavior of AlCoCrFeNi high entropy alloy at various nanoscratching conditions

High-entropy alloys (HEAs) have garnered significant interest in recent years due to their exceptional properties. Among the HEAs, the AlCoCrFeNi HEA has been extensively studied due to its outstanding thermal stability and mechanical properties. However, limited attention has been given to its tribological behavior under high temperature and high velocity conditions. In this study, we first investigate the effect of temperature, scratching velocity, and scratching depth on the tribological behavior of AlCoCrFeNi HEA at the atomic level employing molecular dynamics method. The AlCoCrFeNi HEA exhibits good wear resistance at high temperature due to fewer dislocations to nucleation and slip. Regardless of a significant increase in scratching velocity, there is little difference in the wear volume, indicating that the AlCoCrFeNi HEA still maintains excellent wear resistance even under extremely high scratching velocity. The stacking fault tetrahedron is generated in the AlCoCrFeNi HEA under the large scratching depths of 1.5 nm and 2.0 nm, implying that the wear resistance of AlCoCrFeNi HEA would be improved after the nanoscratching with a relatively large scratching depth. These findings are highly significant for expanding the application potential of AlCoCrFeNi HEA under extreme conditions and provide profound insights into the tribological behavior of the HEA.

Nanoscale friction behavior and deformation during copper chemical mechanical polishing process.

The mechanical characteristics and deformation behavior of Cu material under the nanoscratching through a diamond tooltip on the workpiece are studied using molecular dynamics (MD) simulation. Effects of scratching velocity, scratching depth, workpiece temperature, and grain size on the total force, shear strain, pile-up, shear stress, workpiece temperature, and phase transformation are investigated. The results reveal that increasing the scratching velocity leads to higher oscillation in total force, greater shear strain and shear stress, higher pile-up on the workpiece surface, and higher workpiece temperatures. The effect of the scratching velocity on phase transformation shows that most of the dislocation is a transformation structure from the FCC structure to the HCP, BCC, and other structures in all workpieces during the nanoscratching process. In addition, with increasing the scratching depth, material pile-up becomes more prominent, consequently elevating the contact area between the diamond tooltip and the workpiece, which simultaneously leads to an increase in total force, shear strain, pile-up, shear stress, and workpiece temperature. The MD simulation results revealed that the subsurface region of nanoscratched Cu single-crystal experiences the formation of stacking faults, vacancy defects, and cluster vacancies. In studying the effect of workpiece temperature, the results show that higher temperatures lead to the decline of scratching force, high plastic deformation, increased shear strain and stress, lower pile-up height, and high transition from the FCC structure to both other and BCC structures. For polycrystalline structures, the force curves occur in the oscillation state in all cases of different grain sizes because of the dislocation deformation during the cutting process. The maximum force decreases with diminishing grain size, attributed to the inverse Hall-Petch relation. As the grain size increases, leading to a decrease in the shear strain, stress, and an uneven pile up; also, the HCP structure rises with decreasing grain boundary and the partial dislocation and stacking fault mobilize inside grains. By using molecular dynamics (MD) simulation based on the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) software, all molecular interactions were described by the Lennard-Jones (LJ) and embedded atom method (EAM) potentials. In order to mitigate the effects of temperature fluctuations, the system employs an isothermal and isobaric (NPT) ensemble for precise temperature control. The temperature was set as 300 K and the time step was 1 fs (femtosecond).

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.

Study on scratch hardness in ultrasonic vibration-assisted scratching based on instantaneous contact analysis

The limited knowledge of scratch hardness in ultrasonic vibration-assisted scratch (UVAS) impedes a comprehensive understanding of the abrasive wear process with ultrasonic vibration. The main challenge is the complex kinematic-geometric characteristic of instantaneous contact induced by ultrasonic vibration and the abrasive particle. This paper proposed a novel method to describe the contact behavior exerted by ultrasonic vibration in multiple directions. The wear behavior of the indenter in the UVAS test was analyzed, and the indenter surface was measured to calculate the instantaneous contact area. Based on the developed model and the UVAS test, the effects of ultrasonic vibration on scratch hardness with varying scratch velocity and cutting depth are evaluated. It could be found that the scratch hardness for UVAS was reduced compared to that of common scratch owing to the changed contact states. This study provides an effective tool to capture the instantaneous contact state with a complex moving path and predicts the scratch hardness under ultrasonic vibration through common scratch tests.

Mechanical properties and deformation mechanisms of (Ti0.2Zr0.2Nb0.2Hf0.2Ta0.2)C high‐entropy ceramics characterized by nanoindentation and scratch tests

High-entropy carbides ceramics (HECCs) have attracted extensive attention for their broad application prospects in harsh environments, due to the excellent properties. In this work, the (Ti0.2Zr0.2Nb0.2Hf0.2Ta0.2)C HECCs were prepared using spark plasma sintering at 1800 °C. Then, mechanical properties of HECCs were tested by nanoindentation and scratch tests under different loading conditions. Finally, the mechanical properties and deformation mechanisms were discussed in detail. The density of sintered HECCs reached 8.98 g/cm3, with a relative density of 95.63%. The HECCs demonstrated a single-phase with rocksalt microstructures. The elastic modulus of HECCs was almost a constant under different strain rates, while the hardness obviously increased as the indentation strain rate increasing. In addition, a simple fitted formula was developed to establish the function of hardness and strain rate. Under a relative low scratch load, the HECCs exhibited complete elastic–plastic deformation, and the material removal mechanism was plastic deformation. With increasing scratch load, the material removal mechanism of HECCs transformed into the combined action of plastic deformation and brittle fracture. Furthermore, the deformation mechanisms of HECCs were also influenced by the scratch velocity. At a higher scratch velocity, more local fractures at the micro-scale occurred, and the numbers and sizes of chips and debris also increased.

Scratch and multi-pass scratch behavior of poly (methyl methacrylate) (PMMA)

Polymer materials with high specific strength properties are widely used in engineering applications. Poly (methyl methacrylate) (PMMA) is a rigid and brittle thermoplastic with a high glass transition temperature. It is used in many engineering applications due to its low density, lightweight, high transparency, chemical resistance, and high toughness properties. Intense research efforts have been carried out in recent years regarding the scratching behavior of polymers. The scratch test is performed by moving a hard abrasive indenter across the surface of relatively soft material and is used to determine the mechanical resistance of the surfaces of materials. Scratches on the surfaces of amorphous polymeric materials such as PMMA cause optical and mechanical performance loss. For this reason, it is important to determine the scratching behavior of materials under different operating conditions. Within the scope of the study, the scratching behavior and multi-pass scratch behavior of PMMA were investigated. Experimental studies were carried out with Rockwell and Vickers abrasive indenters at different scratch force and velocity values. Scratch and wear marks were examined by means of an optical microscope, optical profilometer and Scanning Electron Microscope (SEM), and scratch hardness, volumes removed, surface topographies and surface morphologies are presented. It has been observed that these results vary remarkably depending on the type of abrasive indenter, scratch force and velocity.

Tribological property and subsurface damage of nanotwinned Cu/FeCoCrNi high entropy alloy nanolaminates at various scratching velocities and normal loads

The nanotwinned Cu/FeCoCrNi high entropy alloy crystalline/crystalline nanolaminates (NT Cu/HEA C/CNLs) are studied extensively due to their high strength and great plasticity, but their tribological property is still a mystery. Here, the tribological property and subsurface damage of NT Cu/HEA C/CNLs at various scratching parameters are investigated via atomic simulation. The friction coefficient, wear loss, wear rate, subsurface damage, and dislocation behavior are analyzed. A strong dependence of tribological property and subsurface damage on scratching velocity and normal load is uncovered. The results provide a prediction for wear and damage during the service of NT Cu/HEA C/CNLs, and contribute to insight into the subsurface damage mechanism. The investigation is essential to ensure the service performance and engineering application.

Sliding indentation: failure modes with study of velocity and loading rate

Scratch tests were done at micro and nano scale to study the adhesive strength of the SiCN coatings deposited by magnetron sputtering. SiCN are nanocomposites having different hard phases making them useful as protective coatings. The nature of coating/substrate system got reflected in the failure modes in the scratch track. Nano scratch consisted of a three stage process viz. pre scan, scan and post scan for the elastic recover. Effect of scratch velocity and load were studied. The results give an insight into the behavior of the coating subject to different mechanical conditions and hence its suitability for a particular use.

Experimental study on laminated glass responses of high-speed trains subject to windblown sand particles loading

China has built high-speed railways in desert areas. When high-speed trains run in wind-sand flows, wind pressure and sand impact increase the fracture probability of side-window laminated glass. This paper aims to explore the dynamic response and impact resistance performance of laminated glass in high-speed trains subjected to windborne sand particles loading using full-scale experimental tests. Dynamic pressure tests were carried out using an air cannon on the laminated glass to evaluate the glass response under wind dynamic pressure loading. Sandstone impact tests were conducted to study the laminated glass dynamic behavior during particle impact loading. The study results demonstrate that sand impact loading was the primary factor causing the laminated glass damage. The mixed-mode crack initiation and propagation were driven by the reflected tensile waves and Rayleigh surface waves under sandstone impacts. In addition, a statistical analysis of the scratch velocity of the laminated glass suggested that the size of sandstone and impact angle were sensitive to the scratch velocity in the sand particles impacts. This research provides practical help for designing crack-resistant laminated glass structures for high-speed trains.

Origins of ductile plasticity in a polycrystalline gallium arsenide during scratching: MD simulation study

This paper used molecular dynamics simulation to reveal the origins of the ductile plasticity in polycrystalline gallium arsenide (GaAs) during its nanoscratching. Velocity-controlled nanoscratching tests were performed with a diamond tool to study the friction-induced deformation behaviour of polycrystalline GaAs. Cutting temperature, sub-surface damage depth, cutting stresses, the evolution of dislocations and the subsequent microstructural changes were extracted from the simulation. The simulated MD data indicated that the deformation of polycrystalline GaAs is accompanied by dislocation nucleation in the grain boundaries (GBs) leading to the initiation of plastic deformation. Furthermore, the 1/2〈110〉 is the main type of dislocation responsible for ductile plasticity in polycrystalline GaAs. The magnitude of cutting forces and the extent of sub-surface damage were both observed to reduce with an increase in the scratch velocity whereas the cutting temperature scaled with the cutting velocity. As for the depth of the scratch, an increase in its magnitude increased the cutting forces, temperature and damage-depth. A phenomenon of fluctuation from wave crests to wave troughs in the cutting forces was observed only during the cutting of polycrystalline GaAs and not during the cutting of single-crystal GaAs.

Study on the surface formation mechanism in scratching test with different ultrasonic vibration forms

Rotary ultrasonic machining (RUM) has been considered as an effective approach in the manufacturing of advanced materials such as ceramic matrix composite (CMC). However, the distinct removal mechanisms in RUM with different vibration forms has not been elucidated, which hinders the adoption of RUM technology in the field of material processing. In this research, the ultrasonic-assisted scratching tests of CMC were conducted to reveal the fundamentals of material removal and surface formation. Based on the kinematics of RUM processes, the vibration effects exerted in cutting areas were clarified as impact-separation and reciprocating-polishing, thus two types of diamond indenters have been specially designed for the intermittent and continuous scratching tests, respectively. The scratching force, friction factor and grooves morphology have been analyzed and compared with that of the conventional scratching without vibration. For the intermittent scratching with vertical vibration, it was found that the high frequency impact-separation between indenter and workpiece increased the critical penetration depth of ductile-brittle transition, which can help restrain the cracking defects of CMC. For the continuous scratching with tangential vibration, the overlapping rate was firstly proposed to evaluate the effect of reciprocating polishing. It was shown that higher overlapping rate and larger dynamic shear angle can be achieved by matching the scratching velocity with vibration frequency, which is conducive to obtaining even fiber fracture and better surface integrity. Due to the minimal volume of material removed in each vibration cycle, the scratching resistance was significantly lowered with smaller fluctuation under both vibration forms. Moreover, the diminishing of vibration effectiveness at certain scratching parameters was also discussed. This research work brings in a better understanding on the material removal mechanisms under different effects of ultrasonic vibration, which can provide a guidance for the design and optimization of the vibration assisted processing of advanced materials.

Nanoscale manipulation of materials patterning through thermomechanical nanolithography using atomic force microscopy

We conducted thermomechanical nanolithography to realize nanoscale manipulation of materials patterning on a polymethyl methacrylate thin film. We used atomic force microscopy with a heated tip make a single scratch on the film surface. The error in the machining force caused by the thermal expansion of the tip cantilever was corrected to guarantee the accuracy of machining force by calibrating the machining parameters, including the spring constant of the tip cantilever and the sensitivity coefficient of the optical lever for different tip temperatures. Three kinds of nanostructure including polymer nanowires, nanopit arrays, and nanogrooves were regulated via controlling scratching velocity and the heated temperature. Inspection of the nanopit arrays proved that fabrication of continuous bundles with desired dimensions can be realized by controlling the feed between adjacent scratching paths. The good agreement between the calculated stick–slip friction and observed machining outcomes demonstrated the feasibility of using stick–slip friction to predict the generation of nanopit structures.

Numerical and Experimental Analysis of Material Removal and Surface Defect Mechanism in Scratch Tests of High Volume Fraction SiCp/Al Composites.

This paper addresses a comprehensive and further insight into the sensitivity of material removal and the surface defect formation mechanism to scratch depth during single-grit scratch tests of 50 vol% SiCp/Al composites. The three-dimensional (3D) finite element model with more realistic 3D micro-structure, particle-matrix interfacial behaviors, particle-particle contact behaviors, particle-matrix contact behaviors and a Johnson-Holmquist-Beissel (JHB) model of SiC was developed. The scratch simulation conducted at scratch velocity 10 mm/min and loading rate 40 N/min revealed that the scratch depth plays a crucial role in material removal and the surface forming process. Brittle fracturing of SiC particles and surface defects become more deteriorative under a large scratch depth ranging from 0.0385 to 0.0764 μm. The above phenomenon can be attributed to the influence of scratch depth on SiC particles’ transport; the increase in the amount of SiC particle transport resulting from an increase of scratch depth raises the occurrence of particle-particle collision which provides hard support and shock for the scratched particles; therefore, brittle fracturing gradually becomes the major removal mode of SiC particles as the scratch depth increases. On the deteriorative surface, various defects are observed; i.e., lateral cracks, interfacial debonding, cavies filled with residually broken particles, etc. The von Mises stress distribution shows that SiC particles bear vast majority of load, and thus present greater stress than the surrounding Al matrix. For example: their ratio of 3 to 30 under the scratch depth of 0.011 mm. Namely, SiC particles impede stress diffusion within the Al matrix. Finally, the SEM images of the scratched surface obtained from the single-grit scratch experiments verify the numerical analysis’s results.

Effect of multiple reinforcements (CNT/Si3N4) on hardness, electrical conductivity and friction coefficient of aluminium hybrid composites

Present investigation reports on the development of aluminium hybrid composites using powder metallurgy technique. Two different reinforcements namely silicon nitride (Si3N4) and carbon nanotubes (CNT) were used to reinforce pure aluminium matrix. Ball milled powder morphology and microstructure of hybrid composites were studied using scanning electron microscope to study the dispersion of Si3N4 and CNT.Microstructure studies showed uniform dispersion of both the reinforcements in aluminium matrix. Microhardness was obtained by applying a load of 50 N for dwell period of 20 seconds. Electrical conductivity in terms of %IACS was obtained using Eddy current tester. Coefficient of friction was obtained by conducting scratch test by employing a load of 10 N for a stroke length of 10 mm and scratch velocity of 0.2 mm/sec. Microhardness was found to increase with increasing content CNT content while electrical conductivity was found to decrease. Finally coefficient of friction was found to decrease with increase in CNT content owing to its lubricating nature.

Strain rate and shear-transformation zone response of nanoindentation and nanoscratching on Ni50Zr50 metallic glasses using molecular dynamics

The mechanical properties and deformation behavior of Ni50Zr50 metallic glasses are investigated through nanoindentation and nanoscratching using molecular dynamics simulation. The effects of depth, temperature, and velocity on mechanical properties and deformation behavior of Ni50Zr50 are evaluated. The shear transformation zones become larger as increasing indentation depth or scratching length. The strain rate is sensitivity to the scratching velocity. The indentation force, Young's modulus and hardness increase as increasing velocity, however, decrease at a higher temperature. The scratching force rises with a deeper depth and reduces at a higher temperature. The pile-up increases as increasing indentation and scratching depth, indentation temperature. The hardness values vary from 5.0 to 10.5 GPa. The friction coefficient vibrates around 0.7.

Research on nano-scratching behavior of TiZrHfBeCu(Ni) high entropy bulk metallic glasses

Nanoscratch tests have been conducted to study the tribological behavior of TiZrHfBeCu(Ni) high entropy bulk metallic glasses (HE-BMGs). A classic Zr-based BMG, vit-1 alloy, has been selected as a reference. For all the four adopted alloys, the effect of scratch velocity on the nano-scratch behavior is not obvious. It is found that TiZrHfBeCu(Ni) HE-BMGs possess better nanoscratch resistance than that of vit-1 alloy. Moreover, with the Ni content increasing, the glass transition temperature and hardness increase while the free volume content decreases, resulting in a better nanoscratch resistance. The addition of Ni also changes accumulation mode of the removed chips during the scratching process. Based on the variation of coefficient of friction (COF) during the scratching process, all the four alloys exhibit similar scratching mechanisms, which have been explained in detail.

Study of the formation mechanism of bundle structures using AFM tip-based nanoscratching approach

Abstract To investigate the formation mechanism of bundle structures on polycarbonate (PC) surfaces, atomic force microscopy (AFM) was utilized to scratch a PC sheet. A theoretical model for the AFM tip, which accounted for the friction force exerted on the probe, was established to illustrate the torsion angle of the tip. The formation of bundle structures was determined by a critical friction force, and a stick-slip process was used to explain the formation mechanism. The influence of the scratching parameters, including the scratching angles, normal loads, velocities, and feed values, on the amplitude and wavelength of the bundle structures was studied. These results can provide guidance for the fabrication of higher quality bundle structures on a polymer sample surface.

Influence of Processing Parameters on the Local Scratch Resistance of Cold Sprayed Ti6Al4V Coatings

Ti6Al4V coatings were cold sprayed onto the same bulk alloy at standard conditions, using 800 °C as gas temperature, and a set of new conditions, using 1100°C as gas temperature, which improved coatings performance. Some of these coatings, processed with innovative parameters, were heat treated to promote adhesion and reduce porosity. Scratch tests were performed using a nanoindenter Agilent G200 and the effect of both normal load and scratch velocity were explored. The different mechanisms responsible of wear were evaluated, identifying ploughing and cutting as the main abrasion mechanisms. The wear rate measured in the standard coating was the highest, indicating that this material could not be used to repair the bulk component. However, the abrasion resistance measured in the coatings sprayed at 1100°C was similar to that found in the bulk substrate. Therefore, cold spray could be used for repairing using the new conditions evaluated in this work.