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Tribology behaviors of energetic crystals play critical roles in the friction-induced hotspot in high-energy explosive, however, the binder and energetic crystals are not distinguished properly in previous investigations. In this study, for the first time, the nanoscale friction of β-octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (β-HMX) crystal is studied with nanoscratch tests under the ramping load mode. The results show that the nanoscale friction and wear of β-HMX crystal, as a typical energetic material, is highly depended on the applied load. The friction coefficient of β-HMX crystal is initially high when no discernible wear is observed, and then it decreases to a stable value which varies from ∼0.2 to ∼0.7, depending on the applied load, scratch direction, and crystal planes. The β-HMX (011) surfaces show weakly friction and wear anisotropy behavior; in contrast, the β-HMX (110) surfaces show strongly friction and wear anisotropy behavior where the friction coefficient, critical load for the elastic—plastic deformation transition and plastic—cracking deformation transition, and deformation index at higher normal load are highly depended on the scratch directions. Further analyses indicate the slip system and direction of β-HMX surfaces play key roles in determining the nanoscale friction and wear of β-HMX surfaces. The obtained results can provide deeper insight into the friction and wear of energetic crystal materials. [ABSTRACT FROM AUTHOR]

The nanotribological properties of aluminum gallium nitride (AlxGa1−xN) epitaxial films grown on low-temperature-grown GaN/AlN/Si substrates were investigated using a nanoscratch system. It was confirmed that the Al compositions played an important role, which was directly influencing the strength of the bonding forces and the shear resistance. It was verified that the measured friction coefficient (μ) values of the AlxGa1−xN films from the Al compositions (where x = 0.065, 0.085, and 0.137) were in the range of 0.8, 0.5, and 0.3, respectively, for Fn = 2000 μN and 0.12, 0.9, and 0.7, respectively, for Fn = 4000 μN. The values of μ were found to decrease with the increases in the Al compositions. We concluded that the Al composition played an important role in the reconstruction of the crystallites, which induced the transition phenomenon of brittleness to ductility in the AlxGa1−xN system. [ABSTRACT FROM AUTHOR]

Abstract Tribology behaviors of energetic crystals play critical roles in the friction-induced hotspot in high-energy explosive, however, the binder and energetic crystals are not distinguished properly in previous investigations. In this study, for the first time, the nanoscale friction of β-octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (β-HMX) crystal is studied with nanoscratch tests under the ramping load mode. The results show that the nanoscale friction and wear of β-HMX crystal, as a typical energetic material, is highly depended on the applied load. The friction coefficient of β-HMX crystal is initially high when no discernible wear is observed, and then it decreases to a stable value which varies from ∼0.2 to ∼0.7, depending on the applied load, scratch direction, and crystal planes. The β-HMX (011) surfaces show weakly friction and wear anisotropy behavior; in contrast, the β-HMX (110) surfaces show strongly friction and wear anisotropy behavior where the friction coefficient, critical load for the elastic—plastic deformation transition and plastic—cracking deformation transition, and deformation index at higher normal load are highly depended on the scratch directions. Further analyses indicate the slip system and direction of β-HMX surfaces play key roles in determining the nanoscale friction and wear of β-HMX surfaces. The obtained results can provide deeper insight into the friction and wear of energetic crystal materials.

The nanotribological properties of aluminum gallium nitride (AlxGa1−xN) epitaxial films grown on low-temperature-grown GaN/AlN/Si substrates were investigated using a nanoscratch system. It was confirmed that the Al compositions played an important role, which was directly influencing the strength of the bonding forces and the shear resistance. It was verified that the measured friction coefficient (μ) values of the AlxGa1−xN films from the Al compositions (where x = 0.065, 0.085, and 0.137) were in the range of 0.8, 0.5, and 0.3, respectively, for Fn = 2000 μN and 0.12, 0.9, and 0.7, respectively, for Fn = 4000 μN. The values of μ were found to decrease with the increases in the Al compositions. We concluded that the Al composition played an important role in the reconstruction of the crystallites, which induced the transition phenomenon of brittleness to ductility in the AlxGa1−xN system.

• The single crystal PdSe 2 maintained 83% of its original volume after undergoing abrasion, demonstrating the exceptional elasticity of its surface. • Thanks to its strain hardening and sensitivity to strain rate, PdSe2 exhibits ductility like aluminum, enabling it to withstand considerable deformation without compromising its structural integrity. • The examination of its creep behavior revealed size-dependent mechanical endurance under constant load. • Strain hardening measurements yielded n = 0.21 ± 0.07, highlighting the material's high ductility and elasticity, making it ideal for vibration-proof applications in flexible electronics. Palladium diselenide (PdSe 2), a transition-metal dichalcogenide (TMDC), has received interest for its intriguing optical and electrical characteristics. Despite its relevance for flexible electronics, its mechanical properties have been only scarcely investigated. In this work, we examined time-dependent mechanical response, wear, and nanoductility of PdSe 2 grown using chemical vapor transport. Specifically, we measured hardness, elastic modulus, creep characteristics, activation volume, strain rate sensitivity, and wear resistance using nanoindentation and nanoscratch experiments. The obtained values of Young's modulus and hardness are promising for flexible electronic applications. Due to its strain hardening and strain-rate sensitivity, PdSe 2 is ductile like aluminum and could endure significant deformation without losing structural integrity. The investigation of the creep behavior showed its size-dependent mechanical endurance under steady load, which is important for device dependability. Additionally, activation volume calculations indicate dislocation dynamics and processes during deformation, revealing the material's reaction to different mechanical loading conditions. Our nanoscratch experiments showed resilience to surface wear, confirming its suitability for durable flexible electronic devices. The significant elasticity of PdSe 2 , facilitating substantial recovery after deformation, renders it well-suited for flexible and wearable electronic devices requiring the maintenance of electrical continuity even under mechanical stress. The results of our mechanical characterization will open the door to the design and manufacturing of next generation PdSe 2 -based flexible electronic devices. [ABSTRACT FROM AUTHOR]

TiAlN film was deposited on Cr2O3‐coated plasma‐nitrided DAC‐10 tool steel to obtained multilayer Cr2O3/TiAlN coating layer using cathodic arc deposition technique. The structural make‐up of the coating was characterized using Atomic Force Microscopy (AFM) and X‐ray diffraction methods, and the mechanical properties were evaluated using nanoindentation and nanoscratch test. The structural phases of the coating indicated the presence of crystalline CrO structure and cubic TiAlN phases. The coating showcased improved hardness (38 GPa), elastic modulus (387 GPa), and adhesion along with appreciable H/E (0.09) and H3/E2 (0.366 GPa) attributes. Further, friction‐induced wear behavior of the coating was investigated against steel and Al2O3 counterbodies under dry sliding conditions. The wear behavior of the coating was greatly influenced by its hardness and deformation properties and frictional behavior of the counterbodies. More spikes and fluctuation were observed in the frictional curve against Al2O3 counterbody attributed to the emanation of TiO2, Cr2O3, and Al2O3 compounds due to dry sliding leading to the formation of flakes and delamination induced debris. Against the steel counterbody, the coating mainly formed a typical smooth glossy surface ascribed to the formation of Fe2O3 compound on the worn surface. [ABSTRACT FROM AUTHOR]

In this study, nanoscratch experiments using side-forward multiple scans by friction force microscope with triangular pyramidal monocrystalline diamond tip were conducted on a (0001) plane sapphire wafer substrate to clarify the ductile-regime machining mechanism including its anisotropy. Various characteristics, such as scratch force, depth and specific energy for each scratch direction on C-plane of sapphire, were manifested by a friction force microscope, and the specific scratch energy showed a trend of three-fold symmetry. Subsequently, cutting chips which adhere to the diamond tip exhibited plastic deformations features were testified by a scanning election microscope. Based on slip/twinning systems of sapphire, Schmid factor was calculated for each scratch direction using the resultant force, and the calculated Schmid factors on the rhombohedral planes became the highest. Following the results, the resolved shear stresses along the twinning directions on the rhombohedral planes were calculated using a simple chip formation model, and they were several times larger than the critical resolved shear stress for rhombohedral twinning. As a result, it was found that when the scratch direction is set so that one of the three faces of the diamond tip is close to parallel to one of the rhombohedral planes, the rhombohedral plane acts as the chip shear plane and the specific scratch/cutting energy can be minimized. The cross-sectional transmission electron microscope images of scratched sub-surface also distinctly displayed the existence of subsurface damages consisting of twins and stacking faults relating rhombohedral planes. • Nanoscratch tests are conducted on a C-plane sapphire wafer using side-forward multiple scans by an FFM for various scratch directions and resulting in the specific scratch/cutting energy shows three-fold symmetry. • Schmid factor in each scratch direction is calculated using the resultant force obtained in the experiment, and it is confirmed that rhombohedral twinning is most likely to occur. • The resolved shear stress is several times larger than the minimum critical shear stress needed for rhombohedral twinning. • When the scratch direction is set so that one of the three faces of the diamond tip is close to parallel to one of the rhombohedral planes, the rhombohedral plane acts as the chip shear plane and the specific scratch/cutting energy is minimized. [ABSTRACT FROM AUTHOR]

Laser powder bed fusion (LPBF) is an additive manufacturing (AM) technique for the fabrication of components with a complex design, and it is particularly appropriate for structural applications in automotive and air‐space industries. Aluminum matrix composites (AMCs) are promising materials for these uses because they are ductile, light weight, and have an excellent strength‐to‐weight ratio. Herein, a study on microstructure, hardness, and the nanoscale tribological properties of the AlSi10Mg alloy with and without ceramic particles is presented. AMCs are realized with different compositions: 10 wt% of microsize TiB2, 1 wt% of nanosize TiB2, 0.5 wt% of nanosize SiO2, and 0.5 wt% of nanosize MgAl2O4. It is found that the nanocomposites show a lower coefficient of friction (COF), whereas in the case of microsize TiB2 reinforcement, the COF is higher than with either nanosize reinforcements or AlSi10Mg alloy without reinforcement. Results indicate that the interfacial bond between the matrix and the particles of the ceramic reinforcement has a crucial role in wear processes. [ABSTRACT FROM AUTHOR]

Cryogenic treatments are increasingly used to improve the wear resistance of various steel alloys by means of transformation of retained austenite, deformation of virgin martensite and carbide refinement. In this work the nanotribological behavior and mechanical properties at the nano-scale of cryogenically and conventionally treated AISI 420 martensitic stainless steel were evaluated. Conventionally treated specimens were subjected to quenching and annealing, while the deep cryogenically treated samples were quenched, soaked in liquid nitrogen for 2 h and annealed. The elastic–plastic parameters of the materials were assessed by nanoindentation tests under displacement control, while the friction behavior and wear rate were evaluated by a nanoscratch testing methodology that it is used for the first time in steels. It was found that cryogenic treatments increased both hardness and elastic limit of a low-carbon martensitic stainless steel, while its tribological performance was enhanced marginally.

In nanoscratch testing it is observed that the normal and tangential forces do not increase linearly. This behavior results in ploughing friction coefficients that vary with nanoindenter penetration depth. Lafaye and Troyon conducted research on ductile materials that concluded this is due to the nanoindenter not having an ideally sharp tip, but rather a blunt spherical one. The friction coefficient model, applied to brittle materials in this research, uses a previously published analytical friction coefficient model as its foundation, and extends it to include material-specific characteristics that effect friction coefficient behavior. Through the comparison between experiment and modeling, material characteristics such as pileup and nanoindenter contact area were found to aid in properly describing the friction coefficient of brittle materials. [ABSTRACT FROM AUTHOR]

In nanoscratch experiments, the frictional shear force vector applying on each element of the contact surface between the nanoindenter and material is in the direction of material flow lines or relative displacement vectors. In this paper, the material flow lines in the nanoscratch test around the Berkovich nanoindenter in the face-forward orientation are investigated. The finite element simulation of nanoscratch test is conducted to calculate and track the trajectory of the material points located on the material surface. The material flow lines around the nanoindenter are qualitatively and quantitatively explained and a new method entitled focal point method is proposed to describe the material flow lines in the contact surface. The evolution of the material flow lines in terms of the material properties and local friction coefficient is studied. The adhesive friction coefficient is calculated using the pattern of flow lines obtained by the focal point method. There is a close agreement between the predicted friction coefficients and those obtained from the finite element simulation and experiment, so that the error percent is about 5.7%. [ABSTRACT FROM AUTHOR]

In this work, three case studies are reported, namely carbon nanotube/polyvinyl butyral composites, MWCNTs/polydimethylsiloxane-based coatings and vertically aligned CNT forest array, of which the friction and resistance to wear/deformation were assessed through nanoindentation/nanoscratch. Additional deformation parameters and findings are also addressed and discussed; namely, material deformation upwards (pile-up) or downwards (sink-in) with respect to the indented surface plane, hardness to modulus ratio (index of resistance to wear) and coefficient of friction. The enhancement of the scratch resistance due to the incorporation of CNTs in a polymer matrix is investigated. For the case of the forest structure, sliding between neighboring nanotubes is identified, while, through ploughing of the tip, local deformation and the extent of plasticity are also addressed. [ABSTRACT FROM AUTHOR]

Large-scale molecular dynamics simulations are carried out to investigate the friction behavior of nanocrystalline nickel (Ni) at low temperature. Grain sizes ranging from 4–11 nm are used to explore the behavior of nanocrystalline Ni near the Hall-Petch breakdown. Effects of grain size, grain morphology and scratch depth on coefficient of friction (COF) and deformation mechanism of nanocrystalline Ni are investigated. Reduction of the COF with the refinement of grain size in nanocrystalline nickel is observed, however, for a grain size of 5 nm this trend is observed to be reversed. It is also found that scratch depth can influence the estimation of friction behavior of nanocrystalline nickel. [ABSTRACT FROM AUTHOR]

From an environmental and cost-effective perspective, a number of research challenges can be found for electronics, household, but especially in the automotive polymer parts industry. Reducing synthesis steps, parts coating and painting, or other solvent-assisted processes, have been identified as major constrains for the existing technologies. Therefore, simple polymer processing routes (mixing, extrusion, injection moulding) were used for obtaining PMMA/HNT nanocomposites. By these techniques, an automotive-grade polymethylmethacrylate (PMMA) was modified with halloysite nanotubes (HNT) and an eco-friendly additive N,N′-ethylenebis(stearamide) (EBS) to improve nanomechanical properties involved in scratch resistance, mechanical properties (balance between tensile strength and impact resistance) without diminishing other properties. The relationship between morphological/structural (XRD, TEM, FTIR) and tribological (friction) properties of PMMA nanocomposites were investigated. A synergistic effect was found between HNT and EBS in the PMMA matrix. The synergy was attained by the phase distribution resulted from the selective interaction between partners and favourable processing conditions. Modification of HNT with EBS improved the dispersion of nanoparticles in the polymer matrix by increasing their interfacial compatibility through hydrogen bonding established by amide groups with aluminol groups. The increased interfacial adhesion further improved the nanocomposite scratch resistance. The PMMA/HNT-EBS nanocomposite had a lower coefficient of friction and lower scratch penetration depth than PMMA/HNT nanocomposite.

• Nanoindentation and scratch tests were performed multilayer thin film metallic glasses (TFMG). • Failure of multilayer TFMG is greatly influenced by modulation ratio and layer pattern. • Thin film with layer pattern (layer 1 / layer 2) = (Zr55 / Zr65) show better tribological performances. • Tribological performance of multilayer TFMG system can be controlled by changing layer pattern. A nanoscratch technique to investigate the deformation and failure characteristics of multilayer thin film metallic glasses (TFMGs) is described. Nanoscratch experiments were performed on Zr-based multilayer (bilayer) TFMGs deposited over hard substrates (Si, soda-lime glass). Layer pattern and modulation ratio greatly influence the thin films failures under nanoscratch. When compared with pattern (layer-1 / layer-2) = (Zr65 / Zr55), multilayer TFMGs with layer pattern = (Zr55 / Zr65) shows better tribological performances regardless of substrate type (Si or SLG) under the considered nanoscratch conditions. This study is beneficial to find appropriate combination of layer pattern and modulation ratio to ensure good adhesion between multilayer TFMG and substrate. [ABSTRACT FROM AUTHOR]

In this paper, an analytical model is established to calculate both the ploughing and adhesive friction coefficients of metals in a scratch test with the Berkovich indenters at different tip orientations. Using the finite element analysis of nanoscratch test, the patterns of material flow lines around the indenter at different tip orientations are extracted. The adhesive friction coefficient is predicted based on the average angle of material flow lines along each side of the contact surface. When the scratch direction is between the edge-forward and side-forward orientations, the material pile-up in front of the indenter becomes unbalanced between the area of two sides of the contact surface and it highly affects the ploughing friction coefficient. [ABSTRACT FROM AUTHOR]

ZnMgO films were grown via metal organic vapor phase epitaxy on an M-plane sapphire substrate. We used nanoscratch tests to study the abrasive plow of the films; comparable cases of critical pileup were obtained on both sides of each scratch when the ramped load increased from 0 to 250 μN. The film showed a crack in the bulge edge between the groove at ramped loads of 1000 μN as well as full plastic deformation. The values of μ were 0.14, 0.33, 0.43, and 0.48 for the ramped loads of 250 μN and 0.22, 0.26, 0.28, and 0.33 for the ramped load of 1000 μN. We found that cracking dominated in the case of ZnMgO films during plowing. Lower values of the coefficient of friction and shallower penetration depths were observed at RT, while higher values were observed in the annealed samples. It is suggested that higher growth temperatures induce lower bonding forces and reduce the shear resistances of ZnMgO films. [ABSTRACT FROM AUTHOR]

The single-asperity friction and wear behaviors of Nd-doped phosphate laser glass against a spherical diamond AFM tip were quantitatively investigated with respect to normal load, friction cycles, and velocity. Specific friction and wear equations were proposed to fit the experiment data obtained in the single-pass nanoscratch and multi-pass reciprocating sliding tests, respectively. The contribution of both the interfacial fiction and the plowing friction under specific sliding conditions was analyzed, and the corresponding wear mechanism was discussed. The results would be useful in understanding the mechanisms of friction and material removal in ultra-precision cutting and polishing of glass materials. [ABSTRACT FROM AUTHOR]

Understanding the structure-property relationship is important for guiding the design of metallic glasses with advanced properties. In this work, we employ nanoscratching experiments to establish a correlation between structure and nano-tribological behavior in Zr-based metallic glasses where the structural state of the material is characterized by its fictive temperature, T f. The results indicate that independent of the applied load, the scratching depth and residual depth of the scratch track increase with an increase in T f , which is ascribed to the increase in free volume that metallic glasses experience when they are prepared with higher T f. Furthermore, it was found that the effect of T f on the friction coefficient varied significantly with the applied load: At low loads, adhesion-induced friction dominates so that low- T f samples display higher friction coefficients, which we correlate to their denser packed structure affecting interfacial shear. At high loads, however, plowing becomes dominant, which causes the friction coefficient of low- T f samples to become lower than the ones of high- T f samples and is ultimately a consequence the higher elastic recovery capability for the samples with lower T f. Meanwhile, sudden sink-in events of scratching depth are observed when ramping the load during nanoscratching in the indenter face forward direction, revealing the occurrence of scratch-induced yielding. Thereby, the higher degree to which free volume is available in high- T f samples causes them to show higher plasticity, which in turn is responsible for the higher critical loads at which the sink-in event occurs. This finding implies the possibility of using ramping load scratching to characterize the ductile-to-brittle transition of metallic glasses as an alternative to carrying out time-consuming fracture tests. • Establish the relationship between nano-tribological behavior and structure of Zr-BMGs via their T f. • More free volume in high- T f BMGs lead to weaker scratch-resistance but higher plasticity in BMG. • Low- T f BMGs display higher adhesion friction, attributing to their denser packed structure. • High- T f BMGs show higher plowing friction, relating to their lower elastic recovery capability. [ABSTRACT FROM AUTHOR]

Abstract: Scratch properties of extremely thin (targeted at 0.03–5.0-nm-thick) diamond-like carbon (DLC) films deposited by the filtered cathodic vacuum arc (FCVA) and electron cyclotron resonance chemical vapor deposition (ECR-CVD) methods are investigated. The difference in profiles and friction coefficients of scratches in both the corn and edge directions are evaluated. The difference of scratch properties between deposition methods is clearly evaluated by the scratching in the corn direction. When scratching in the corn direction, the friction coefficient and wear depth of the FCVA-DLC film increased rapidly at critical load, whereas those of the ECR-CVD-DLC film increased gradually even beyond this critical load. These results are deduced to be caused by the differences in the hardness and brittleness of the films. The dependence of nanoscratch friction force and scratch profile on DLC film thickness can reveal differences in mechanical properties that correspond to atomic-scale thickness. [Copyright &y& Elsevier]

Tribological thermostability of carbon film with vertically aligned graphene sheets was studied with annealing temperatures up to 1,750 °C. The carbon film was deposited on silicon carbide substrate by electron cyclotron resonance plasma sputtering. Tribological thermostabilities of the carbon film in terms of friction coefficient, wear life, and nanoscratch depth were investigated by Pin-on-Disk tribometer and atomic force microscopy. The evolution of nanostructure of vertically aligned graphene sheets in the carbon film as a function of annealing temperature was examined by Raman spectroscopy and transmission electron microscopy. The results showed that the friction coefficient, wear life, and nanoscratch depth of the carbon film were thermally stable up to 1,250 °C. When the annealing temperature was 1,500 °C, the friction coefficient and the nanoscratch depth increased, the wear life decreased, but still all were of considerable values. These variations were attributed to the initiation of tubular-like structure originated from graphene sheets stacks. After annealing at 1,750 °C, tribological performances degraded catastrophically due to the abundant formation of tubular-like structures and the appearance of a graphitic interlayer between the film and the substrate. [ABSTRACT FROM AUTHOR]

Abstract: This study present the nanotribological behavior of single-crystalline indium nitride (InN) films onto aluminum nitride (AlN) buffer layers on Si(111) substrates. The surface morphology and friction (μ) were analyzed using atomic force microscopy and nanoscratch system. It is confirmed that the normal force (F n ) measured values of μ of the InN films, from 10 to 60min of etching duration, were in the range from 0.2 to 0.43 for F n =2000μN; 0.25 to 0.58 for F n =6000μN, respectively. It is suggested that the measured values of μ is slightly increased based on the etching duration due to the etching effect on the grain boundary and reduce film quality of InN films. From morphological observations, we compared the sliding resistance against contact-induced damage of the InN films in the presented ploughed of the area. It is confirmed that the contact sliding line is observable due to the increased F n , the following investigation with friction curve and lateral force is studied. [Copyright &y& Elsevier]

Ti-based protective thin films with thicknesses below 100 nm, intended for miniature applications were deposited using physical vapor deposition magnetron sputtering. X-ray diffraction (XRD), scanning electron microscopy, and atomic force microscopy were employed for the assessment of microstructure, morphology, film thickness, surface topography, and roughness. XRD pattern showed the formation of f.c.c TiN, TiCN, and TiC phases with different preferred orientations for films prepared in Ar/N, Ar/N + CH, and Ar/CH gas mixtures, respectively. Nanotribological performance was investigated using multipass nanoscratch technique at variable applied normal loads (100-400 μN). The nanoscale coefficient of friction was found to be in the 0.08-0.1 range, a sufficiently low value showing the potential of these films for miniature applications, such as microelectromechanical systems. The nanowear resistance at mean contact pressures in the range of 5-8.5 GPa for each sample was evaluated in terms of the average residual wear depth and an abrasive-dominated wear mechanism was found. [ABSTRACT FROM AUTHOR]

In this study, nanoindentation and nanoscratching were employed to research on the mechanical anisotropy of CdZnTe (110) and (111) planes, and their effects on the grinding of CdZnTe wafers were studied. The results suggest that the primary slip system is responsible for the anisotropy of hardness and frictional coefficient. It is easy to slip along [image omitted] directions on (110) plane and [image omitted] directions on (111) plane during scratching, hence the frictional coefficient is the lowest compared to that of other directions, and high surface quality could be obtained during grinding along these directions. The problem of embedded abrasives, which is due to the soft nature of CdZnTe crystal, could be solved when using the grinding process instead of the lapping process. [ABSTRACT FROM AUTHOR]

• Low-load scratches compressed the polydopamine (PDA)/polytetrafluoroethylene (PTFE). • PDA aggregates were compressed by low-load scratches and removed by high-load ones. • PDA/PTFE coating failed at a load corresponding to that of PDA aggregate removal. • Large initial wear depths reported in prior studies were due to coating compaction. The scratch behavior of polydopamine (PDA)/polytetrafluoroethylene (PTFE) coatings has traditionally been studied using macro-scale tribometers. However, in this study, a nanoindenter is used to scratch PDA/PTFE coatings on 60NiTi substrate to investigate the nanoscale deformation behavior and failure mechanisms of this coating under various scratch loads. Nanoscratch tests were also performed on the substrate coated only with the adhesive underlayer to study the behavior of PDA under various scratch loads. Scanning electron microscope imaging of the scratches provided further insights to the coating scratch deformation behavior. The study revealed the PDA/PTFE coating failure is strongly correlated with the removal of the PDA particles in the underlayer. The findings also suggest that the compaction of the thin PDA/PTFE coatings could be the main reason for the previously reported large initial wear depth in macro-scale tribology studies. [ABSTRACT FROM AUTHOR]

Abstract: Wear behaviors of Ag/Cu multilayers were evaluated and compared using nanoscratch techniques under a ramping load. Scratch grooves were examined using scanning electron microscopy (SEM) and in situ cross-section scan. It was found that the friction coefficients for all samples have significant difference and the wear resistance is not linearly proportional to the hardness. These discrepancies were suggested to be a result of the transition of the wear mechanism from micro-cutting to micro-ploughing with decreasing periodicity. Multilayer with periodicity Λ =100nm has the highest friction coefficient and wear resistance due to formation of built-up edge. The elastic recovery increases consistently with increasing H/E. [Copyright &y& Elsevier]

Ti/TiB2 nanomultilayer thin films with different bilayer thicknesses λ were deposited onto unheated Si(100) wafers (for mechanical analyses) and AISI M42 tool steels (for tribological measurements) by unbalanced dc magnetron sputtering. The effects of different λ values on mechanical and tribological properties were investigated. These films were characterised and analysed in terms of their hardness by microindentation measurements, their surface root mean square roughness by AFM, their stress by an optical interference method, and their friction and wear behaviors by Rockwell-C testing, nano-/micro-scratch testing, dynamic impact testing and pin on disc tribometer. It was found that the mechanical and tribological properties of multilayer films (typically 158±010 µm in thickness) were closely related to λ (varied from 11 to 98 nm). For the best multilayer film with λ519 nm, a maximum hardness of ∼325 GPa was achieved and the best cohesive and adhesive strength was evidenced in terms of critical load values of LC1 (∼26 N) and LC2 (∼62 N). Moreover, by dynamic impact testing this multilayer film could endure impact cycles up to 4 × 105 without adhesive failure. However, when the λ was further decreased to 11 nm, the hardness, cohesive and adhesive strength were decreased due to a high level of intermixing and lack of a layered structure. It was also found that the nanoscratch test under single pass and constant load conditions showed that the frictional coefficients decreased with λ and increased with normal load due to the ploughing effect. The enhanced hardness in the multilayer films with small λ values improved the wear resistance and lowered the frictional coefficients. These adhesive properties and wear performance are also discussed on the basis of mechanical properties and wear mechanisms. [ABSTRACT FROM AUTHOR]

Abstract: Hafnium diboride (HfB2) offers an excellent combination of high bulk hardness (29GPa), high melting point (3295°C) and high wear resistance, thus making it an attractive material for wear resistant coatings. In this work, the nanoscale friction response of as-deposited and annealed HfB2 films is reported. The films were subjected to nanoscratch experimentation and the material response was investigated by measuring lateral forces to obtain friction coefficient, and by calculating Hertzian contact pressures. Both as-deposited and annealed films show favorable friction behavior with respect to TiN. While as-deposited HfB2 and TiN deform plastically at all normal loads used in the experiments, annealed HfB2, which is nanocrystalline in contrast to the X-ray amorphous as-deposited coatings, responds elastically at lower loads. The friction behavior of the films shows no significant dependence on sliding velocity indicating negligible effect of frictional heating. The films, however, exhibit a prolonged effect of running-in which is present over the entire duration of the experiments and leads to increase in the friction coefficient with number of passes. Annealed films display narrower and shallower scratch grooves, leading to a higher nanoscratch resistance. The excellent overall response of annealed HfB2 films to nanoscratch testing confirms the potential of these films for wear resistant coatings. [Copyright &y& Elsevier]

Abstract: In this investigation, nanoindentation, nanoscratch and nanowear tests were done in order to study the nanomechanical and nanotribological properties of the chromium carbide nanostructured thin films. Chromium carbide films were synthesized by rf sputtering from a Cr3C2 target on magnesium oxide substrate. The samples were characterized by X-ray diffraction and grazing X-ray reflectivity. All the films have a thickness of 300nm. A pyramidal Berkovich indenter diamond tip was used for nanomechanical testing. The residual wear depth of the samples was examined using an atomic force microscope (AFM). In this study, an experimental method adapted to the nanowear properties was explored. We have studied the influence of the substrate temperature on the structural, mechanical and tribological properties of chromium carbide films. We have shown that Cr3C2 films deposited at a substrate temperature up to 600°C exhibit a better wear resistance and a hardness value higher than what is measured in the case of the films deposited at room temperature. [Copyright &y& Elsevier]

Abstract: In nanoscratch testing, it is generally observed that the lateral force does not linearly increase with the applied load. In other words, the apparent friction coefficient, defined as the ratio between the lateral force and the applied load, does not have a constant value. This one may be split into two components, the adhesion coefficient and the ploughing coefficient due to the surface deformation. In the present paper, simulations of the evolution of the ploughing friction coefficient estimated from the model of a conical indenter with a blunted spherical tip taking into account the elastic recovery is compared to the experimental values of the apparent friction coefficient. The comparison of simulations and experiments shows that the non-linear behaviour of the lateral force with the applied load may be mainly explained by the fact that the indenter is not perfectly sharp but has a rounded extremity. [Copyright &y& Elsevier]

Abstract: Human hair (∼50–100μm in diameter) is a nanocomposite biological fiber with well-characterized microstructures, and is of great interest for both cosmetic science and materials science. Characterization of nanotribological and nanomechanical properties of human hair including the coefficient of friction and scratch resistance is essential to develop better shampoo and conditioner products and advance biological and cosmetic science. In this paper, the coefficient of friction and scratch resistance of Caucasian and Asian hair at virgin, chemo-mechanically damaged, and conditioner-treated conditions are measured using a nanoscratch technique with a Nano Indenter II system. The scratch tests were performed on both the single cuticle cell and multiple cuticle cells of each hair sample, and the scratch wear tracks were studied using scanning electron microscopy (SEM) after the scratch tests. The effect of soaking on the coefficient of friction, scratch resistance, hardness and Young''s modulus of hair surface were also studied by performing experiments on hair samples which had been soaked in de-ionized water for 5min. The nanotribological and nanomechanical properties of human hair as a function of hair structure (hair of different ethnicity), damage, treatment and soaking are discussed. [Copyright &y& Elsevier]

Abstract: The analysis of the wear resistance of polymeric fibres requires a better understanding of both their abrasive scratch behaviour and their frictional response. These aspects have been investigated at the nanometre scale using the resources of a modified surface force apparatus. In an attempt to simulate the abrasive wear losses, nanomachining experiments have been carried out which consists in the repeated scratching of a portion of the fibre surface by the rigid indenter. However, an analysis of the resulting surface topography indicated a significant plastic grooving of the fibre surface with no evidence of wear losses as it was observed at the macroscopic scale. Single pass nanoscratch experiments realised at various sliding speeds also allow discussing the relative contributions of both the material viscoplasticity and the tip/material local interactions on the frictional response. When the sliding speed was incrementally changed during a scratch experiment, it was observed that the associated friction variation was accommodated on a 50nm distance, independently of the sliding speed. [Copyright &y& Elsevier]

DLC film interfacial fatigue and changes in friction coefficient phenomena were investigated during quasi-static nanoindentation/scratch while the sample surface was excited ultrasonically. An original experimental setup combines nanoindenter, SPM scanner and ultrasonic transducer operating in an elastic standing wave mode. Nanoindentation loading–unloading curves revealed delamination induced excursions after a certain number of ultrasonic loading cycles. Drastic changes in quasi-statically monitored friction coefficient during nanoscratch were correlated with sample vibration amplitude and loading force. Resulting indentation/scratch film delamination effects and surface wear patterns were examined by an in situ SPM technique. Ultrasonically excited nanoindentation and nanoscratch techniques can be considered as fast and qualitative methods to characterize critical tribo surfaces for data storage devices. [Copyright &y& Elsevier]

In this study, friction and wear behaviors of an amorphous Zr 20 Ti 20 Cu 20 Ni 20 Be 20 high-entropy alloy (a-HEA) were characterized using a nanoscratch method. Scratch tests were carried out under both ramping and constant loading conditions to measure the coefficient of friction (COF) and wear resistance of the amorphous alloy. The morphology of scratched surface and subsurface was further examined using scanning and transmission electron microscopes. It was found that friction behavior of the a-HEA can be divided into two regions: elastic and plastic. In the elastic region, the COF dramatically decreases with increasing normal force, however, it monotonically increases in the plastic region. Morphological observation indicated that brittle fracture dominated in the plastic region, which was consistent with the result that a series of load serrations were accompanied by the formation of brittle cracks along the scratched track. Wear performance of the a-HEA was also evaluated and compared with "conventional" metallic glasses and crystalline high-entropy alloys. As a result of high hardness and large elastic recovery, the current a-HEA exhibited good wear resistance and low COF, behaved more like brittle amorphous alloys rather than ductile high-entropy alloys. Image 1 • Friction and wear behaviors of an amorphous high-entropy alloy (a-HEA) were studied using a nanoscratch technique. • Friction of the a -HEA can generally be divided into two regions: elastic and plastic. • Brittle fracture dominates the plastic deformation, as manifested by load serrations and scratched surface morphology. • As a result of high hardness and large elastic recovery, the a-HEA exhibited good wear resistance and low COF. [ABSTRACT FROM AUTHOR]

From an environmental and cost-effective perspective, a number of research challenges can be found for electronics, household, but especially in the automotive polymer parts industry. Reducing synthesis steps, parts coating and painting, or other solvent-assisted processes, have been identified as major constrains for the existing technologies. Therefore, simple polymer processing routes (mixing, extrusion, injection moulding) were used for obtaining PMMA/HNT nanocomposites. By these techniques, an automotive-grade polymethylmethacrylate (PMMA) was modified with halloysite nanotubes (HNT) and an eco-friendly additive N,N′-ethylenebis(stearamide) (EBS) to improve nanomechanical properties involved in scratch resistance, mechanical properties (balance between tensile strength and impact resistance) without diminishing other properties. The relationship between morphological/structural (XRD, TEM, FTIR) and tribological (friction) properties of PMMA nanocomposites were investigated. A synergistic effect was found between HNT and EBS in the PMMA matrix. The synergy was attained by the phase distribution resulted from the selective interaction between partners and favourable processing conditions. Modification of HNT with EBS improved the dispersion of nanoparticles in the polymer matrix by increasing their interfacial compatibility through hydrogen bonding established by amide groups with aluminol groups. The increased interfacial adhesion further improved the nanocomposite scratch resistance. The PMMA/HNT-EBS nanocomposite had a lower coefficient of friction and lower scratch penetration depth than PMMA/HNT nanocomposite. [ABSTRACT FROM AUTHOR]