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Strength and wear properties of metal matrix composites are important because of their numerous applications in automotive and aerospace industries. In the present study, Al-Cu alloy-based nanocomposites reinforced with different volume percentages of Al2O3 particles were developed by reactive stir mixing of nanocrystalline CuO powder in molten Al. X-ray diffraction (XRD) patterns of the resulting nanocomposites revealed the presence of Al2O3 reinforcements and CuAl2 intermetallic particles. Microstructural characteristics of the samples were investigated and analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). TEM analysis revealed the presence of geometrically necessary dislocations and microcracks inside the sample. Average dislocation density was determined by the modified Warren–Averbach method from XRD patterns. The near-surface wear behavior of the composites was studied by nanoscratch tests. The results were correlated with the microstructural features and dislocation density. [ABSTRACT FROM AUTHOR]

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]

Single crystal aluminum nitride (AlN) as a new generation of ultra-wide band gap semiconductor materials is the preferred substrate material for high power, high RF devices, but single crystal AlN is hard and difficult to process. To obtain high-quality substrate requires comprehensive understanding of the material deformation and removal mechanism. In this paper, the molecular dynamics simulation method is used to scratch the AlN on the (0001) plane. Set up multiple sets of scratch depths to study the elastic-plastic deformation, material removal mechanism and crack evolution of single crystal AlN. The simulation results show that with the increase of scratch depth, the single crystal AlN workpiece undergoes elastic deformation to continuous plastic deformation and then to brittle fracture. The deformation mode in the elastic stage is phase-change, from wurtzite-structure to graphite-like (GL) phase. The plastic deformation of single crystal AlN is achieved by dislocations moving on the basal and pyramidal planes, and horizontally extended stacking faults. There is almost no subsurface damage below the stacking faults. When the scratch depth exceeds 6 nm, the material will undergo brittle fracture, and the fracture surface is the cleavage surface {10-10} of single crystal AlN. [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]

This research shows different hard Ti-based coatings deposited over steel substrates using the physical vapor deposition (PVD) method. The graded coating of the three produced Ti, TiN and TiCN were assessed using phase composition analysis and spectroscopy study. The microstructure characterization was studied by X-ray Photoelectron spectroscopy (XPS), Scanning Electron Microscopy (SEM), and transmission electron microscopy (TEM). The results show that integrating Ti interlayer with subsequent TiN/TICN layers can be considered a suitable way to yield hard Ti-based coating with enhanced mechanical and tribological behavior due to nitride and carbonitride phases formed from the breakdown of carbon and nitrogen atoms. The elastic modulus and hardness of all layers were identified by nanoindentation and utilized to achieve yield strength. Later, the curvature of the unloading step and elastic properties are used for finding flow behavior parameters in terms of work hardening factors (n and K). The attained findings extracted from the load–displacement curve of both nanoindentation and nano scratch were analyzed to examine the microscopic performance of all three Ti, TiN, and TiCN coatings. Scratch mechanisms analysis in all coatings shows that the main failures in samples are caused by tensile stress stemming from Hertzian cracks. However, as the force increases, the coating surface undergoes an incremental deformation, and failure mode varies to interfacial spallation.

In order to investigate the ultra precision cutting characteristics of monocrystalline silicon, nanoindentation and nanoscratch experiments were conducted on <100 > surface of monocrystalline silicon using a nanoindentation instrument and a Berkovich diamond indenter. In the nanoindentation experiment, the indenter was pressed onto the surface of monocrystalline silicon under 10, 30, and 50 mN loads, respectively. It is found that there are slight fluctuations in the load displacement curve under 30 mN load, while a "pop out" phenomenon occurred under 50 mN load, indicating a sudden stress change and brittle failure of the material, the critical load for brittle-plastic transition of monocrystalline silicon was predicted to be slightly less than 30 mN. Nanoscratch experiments with variable loads from 0 to 100 mN were carried out. According to the loaddisplacement curve, it is observed that monocrystalline silicon scratching can be divided into elastic-plastic removal and brittle removal stages during variable load. In the elastic-plastic removal stage, the load-displacement curve fluctuates smoothly, while in the brittle removal stage, the curve fluctuates significantly. The critical load for the brittle-plastic transition of monocrystalline silicon is 27 mN, and the critical depth is 392 nm. Finally, through the constant load nanoscratch experiment, the surface of monocrystalline silicon was scratched at a constant load of 5, 10, and 20 mN in the plastic processing region, respectively. The surface morphology of monocrystalline silicon after constant load scratch was observed by scanning electron microscopy (SEM). The scratching analysis data shows that the cutting force and elastic recovery rate increases with the increase of load, while the friction coefficient first increases and then decreases. Therefore, in ultra precision machining of monocrystalline silicon, it is necessary to select a reasonable machining load and fully consider the impact of elastic recovery. [ABSTRACT FROM AUTHOR]

In this work, titanium oxide nanotubes (TNTs) were formed by anodic oxidation on the surface of a Ti–6Al–4V alloy. An electrolyte based on ethylene glycol (EG) and ammonium fluoride (NH4F) was used. Different anodizing periods (10, 20, 30, 40, 50, and 60 min) with a constant potential of 60 V were established. The morphology of the TNT array was observed by scanning electron microscopy (SEM). The adhesion strength of the TNTs to the Ti–6Al–4V surface was evaluated using nanoscratch tests. The critical load of the different TNT layers was determined from the analysis of the groove of the nanoindenter path. It ranged from 0 mN for the samples exposed to 10 min of anodization to 47.0 ± 3.0 mN for samples exposed to 50 min. These results indicate the TNT layers formed at 50 min presented the best substrate adhesion among the specimen tested. [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.

In this study, the structural integrity of mullite (3Al2O3·2SiO2) films, deposited on silicon carbide (SiC) substrates using chemical vapor deposition (CVD), was investigated via increasing load nanoscratch tests. The films were configured by mullite columns of stoichiometric composition growing from a silica-rich layer in contact with the SiC substrate. Controlled damage was induced in the 3Al2O3·2SiO2 films at relatively low scratch loads. Radial and lateral cracking were applied until final delamination and repeated chipping were achieved as the load increased. The intrinsic integrity of the 3Al2O3∙2SiO2 film and the performance of the coated 3Al2O3·2SiO2/SiC system, regarded as a structural unit, were analyzed. With the aid of advanced characterization techniques at the surface and subsurface levels, the configuration and morphology of the damage induced in the coated system by the nanoscratch tests were characterized, and the scratch damage micromechanisms were identified. Finally, the adhesion of the film, in terms of energy of adhesion and interfacial fracture toughness, was determined using different models proposed in the literature. The results from this investigation contribute to the understanding of the mechanical performance and structural integrity of EBC/SiC-based systems, which over the past few years have increasingly been implemented in novel applications for gas turbines and aircraft engines.

Despite their vast composition space and promising properties, little is known about the fundamental mechanical behavior of high entropy oxides (HEOs). Here we provide experimental evidence of the nanoscale origin of room temperature deformation in (Co,Cu,Mg,Ni,Zn)O HEOs with different grain sizes. We find that micron-grain (Co,Cu,Mg,Ni,Zn)O deforms predominately through extensive [Formula: see text]{1–10} dislocation slip manifesting as discrete slip bands. Nano-grain (Co,Cu,Mg,Ni,Zn)O, in addition to moderate dislocation slip activity, deforms through grain boundary sliding and intergranular cracking. The significant dislocation-mediated deformation and grain size dependent behavior demonstrates that HEOs have the potential for diverse and highly tailorable mechanical behavior.

The application range of potassium dihydrogen phosphate (KDP) crystals can be expanded by enhancing their surface quality properties. Therefore, a method for controlling the surface-temperature field of various materials was developed to expand the plastic zone to overcome the difficulty in processing KDP crystals. The ductile/brittle transition depth of the KDP crystals was determined using a 38 nm nanoindentation experiment. The nanoscratch experiment revealed the rules of how the transformation depth of the KDP crystals changes with temperatures, and the effect of temperature on the microstructure of the KDP crystals was studied. Finally, KDP crystal surfaces were processed using a UPDFC machine at elevated temperatures. According to our experiments, the surface roughness of the KDP crystal reached 5.275 nm as temperature increased, thus enhancing its surface quality. This method could be applied to other brittle materials. [ABSTRACT FROM AUTHOR]

Despite their vast composition space and promising properties, little is known about the fundamental mechanical behavior of high entropy oxides (HEOs). Here we provide experimental evidence of the nanoscale origin of room temperature deformation in (Co,Cu,Mg,Ni,Zn)O HEOs with different grain sizes. We find that micron-grain (Co,Cu,Mg,Ni,Zn)O deforms predominately through extensive 1 2 <110>{1–10} dislocation slip manifesting as discrete slip bands. Nano-grain (Co,Cu,Mg,Ni,Zn)O, in addition to moderate dislocation slip activity, deforms through grain boundary sliding and intergranular cracking. The significant dislocation-mediated deformation and grain size dependent behavior demonstrates that HEOs have the potential for diverse and highly tailorable mechanical behavior. High entropy oxides (Co,Cu,Mg,Ni,Zn)O exhibit grain size dependent room temperature deformation, with micron-grain samples displaying significant potential for dislocation-mediated deformation and nanocrystalline samples exhibiting grain boundary sliding and micro-cracking. [ABSTRACT FROM AUTHOR]

In this study, the structural integrity of mullite (3Al2O3·2SiO2) films, deposited on silicon carbide (SiC) substrates using chemical vapor deposition (CVD), was investigated via increasing load nanoscratch tests. The films were configured by mullite columns of stoichiometric composition growing from a silica-rich layer in contact with the SiC substrate. Controlled damage was induced in the 3Al2O3·2SiO2 films at relatively low scratch loads. Radial and lateral cracking were applied until final delamination and repeated chipping were achieved as the load increased. The intrinsic integrity of the 3Al2O3∙2SiO2 film and the performance of the coated 3Al2O3·2SiO2/SiC system, regarded as a structural unit, were analyzed. With the aid of advanced characterization techniques at the surface and subsurface levels, the configuration and morphology of the damage induced in the coated system by the nanoscratch tests were characterized, and the scratch damage micromechanisms were identified. Finally, the adhesion of the film, in terms of energy of adhesion and interfacial fracture toughness, was determined using different models proposed in the literature. The results from this investigation contribute to the understanding of the mechanical performance and structural integrity of EBC/SiC-based systems, which over the past few years have increasingly been implemented in novel applications for gas turbines and aircraft engines. [ABSTRACT FROM AUTHOR]

Hydroxyapatite (HAp) was deposited by plasma spraying technique with TiSiN adhesive interlayer on the medical-grade 316 LVM stainless steel. The surface topographies of HAp and HAp/TiSiN were evaluated using X-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The important mechanical properties of the films such as hardness (H) and elastic modulus (E) were determined by the nanoindentation test. Lastly, the adhesion and anti-scratch behaviors of the films were evaluated by Rockwell-C indentation and nanoscratch test, respectively. The elemental analysis showed the values of Ca/P (at.%/at.%) ratio to be 1.80 and 1.59 in HAp and HAp/TiSiN coatings, respectively. The mechanical properties of HAp film with TiSiN interlayer were greatly improved from 1.23±0.26GPa to 10.6±1.12GPa for hardness and from 18±3GPa and 29.8± 5GPa for elastic modulus, respectively. The results of the Rockwell-C indentation test showed a significant reduction in HAp coating delamination with TiSiN interlayer which can be categorized with HF2 or HF3 Daimler–Benz quality ranking. What is more, the nanoscratch profile of HAp coating showed wider scratch with evidence of deformation at the edges which got significantly reduced with the TiSiN interlayer. The results are suggestive of improved mechanical properties, viz. hardness and elastic modulus, and improved adhesion strength of HAp coating with TiSiN interlayer. [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.

Monolithic metal-organic frameworks (MOFs) represent a promising solution for the industrial implementation of this emerging class of multifunctional materials, due to their structural stability. When compared to MOF powders, monoliths exhibit other intriguing properties like hierarchical porosity, that significantly improves volumetric adsorption capacity. The mechanical characterization of MOF monoliths plays a pivotal role in their industrial expansion, but so far, several key aspects remain unclear. In particular, the fracture behavior of MOF monoliths has not been explored. In this work, we studied the initiation and propagation of cracks in four prototypical MOF monoliths, namely ZIF-8, HKUST-1, MIL-68 and MOF-808. We observed that shear faults inside the contact area represent the main failure mechanism of MOF monoliths and are the source of radial cracks. MIL-68 and MOF-808 showed a remarkably high resistance to cracking, which can be ascribed to their consolidated nanostructure.

TiAlN film was deposited with Cr-CrN interlayer (Cr-(CrN/TiAlN)) on DAC-10 tool steel using cathodic arc deposition followed by annealing in vacuum chamber at 700°C temperature. Nanoindentation and nanoscratch test were conducted on as-deposited and annealed samples. The annealed samples showcased improved hardness (8.55 %) and elastic modulus (12.21 %) attributed to the formation of larger grain size (48 nm) and diffusion of Cr atoms from the interlayer. The XRD pattern of the annealed samples revealed Cr diffusion in the TiAlN top layer along with the formation of oxide such as Al2O3. The annealed samples registered lower pile up, indentation depth, higher strain hardening exponent (n = 0.41) and lower plastic work (0.25). Tribological properties such as scratch hardness was improved by 8.84%, whereas coefficient of friction and wear rate was reduced by 22.92% and 35.75%, respectively, after annealing of the coating. The relation between the nanomechanical and scratch properties was indicative of the influence of hardness and strain hardening exponent on the wear properties of the annealed Cr-(CrN/TiAlN) coating. [ABSTRACT FROM AUTHOR]

Silicon (Si) and silver (Ag) doped amorphous carbon (a-C) thin film were deposited on chrome nitrided 316 LVM stainless steel using filtered cathodic vacuum arc (FCVA) deposition technique to obtain Si:a-C and Ag:a-C thin film. The morphology of the films was evaluated using atomic force microscopy, X-ray diffraction, Raman spectroscopy, nanoindentation and nanoscratch tests. The surface quality of Ag:a-C film appeared inferior owing to the formation of Ag agglomerates on the surface. Raman studies indicated higher shifting and narrowing of G-band in Ag:a-C film resulting in increased sp2 hybridization. Also, the ID/IG ratio of Si:a-C film (1.3) was lesser than Ag:a-C (2.3) film indicative of higher sp3 content in the former. This has propounded to improved mechanical attributes such as hardness (24.5 ± 3.8 GPa), elastic modulus (241 ± 14 GPa), H/E (0.103 ± 0.11), H3/E2 (0.282 ± 0.021 GPa) and fracture toughness (2.93 MPa.m1/2) in Si:a-C film. Further, Ag:a-C film suffered severe radial cracks during indentation at higher load owing to debonding. On the other hand, Si:a-C film exhibited the formation of circumferential cracks during indentation attributed to higher compressive stress in the film. What is more, Si:a-C showcased better film adhesion in Rockwell-C adhesion test with lesser delamination at the impression edge. This is further corroborated by microscratch test depicting higher Lc2 value and adhesive energy. [ABSTRACT FROM AUTHOR]

In this work, titanium oxide nanotubes (TNTs) were formed by anodic oxidation on the surface of a Ti–6Al–4V alloy. An electrolyte based on ethylene glycol (EG) and ammonium fluoride (NH4F) was used. Different anodizing periods (10, 20, 30, 40, 50, and 60 min) with a constant potential of 60 V were established. The morphology of the TNT array was observed by scanning electron microscopy (SEM). The adhesion strength of the TNTs to the Ti–6Al–4V surface was evaluated using nanoscratch tests. The critical load of the different TNT layers was determined from the analysis of the groove of the nanoindenter path. It ranged from 0 mN for the samples exposed to 10 min of anodization to 47.0 ± 3.0 mN for samples exposed to 50 min. These results indicate the TNT layers formed at 50 min presented the best substrate adhesion among the specimen tested.

Understanding the deformation mechanism of a brittle material under mechanical loading is of value for unveiling the material removal in an abrasive machining process. In this work, instrumented nanoscratching was performed on the (0001) plane of single crystal gallium nitride (GaN) using a conical diamond indenter and the scratch-induced surface/subsurface deformation patterns were characterized by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A finite element model of scratching was established to relate stress distribution and deformation patterns. The stress threshold for the elastic-plastic deformation transition of the crystal was found being relatively high in comparison to single crystal silicon and gallium oxide. The plastic deformation in the GaN sublayer was dominated by slip, dislocation and lattice distortion under relatively low normal loads, but those defects were accompanied with grain rotation when the load was sufficiently high. The thickness of the damage layer was directly related to the ratio of lateral force to normal force during scratching. Such a force ratio can be used as an indicator for controlling the damage layer thickness during abrasive machining, thus providing a valuable guidance for developing the optimal parameters of an ultraprecision abrasive machining process. [ABSTRACT FROM AUTHOR]

Nanostructured powder particles of Fe3Al and (Fe,Ti)3Al phases were produced using mechanical alloying. These intermetallic phases with a nearly complete density were consolidated by spark plasma sintering. The mechanical properties of the bulk samples, i.e., elasticity modulus, hardness, and plasticity index, and also their tribological behavior were investigated using nanoindentation and nano-scratch tests. It was found that both Fe3Al and (Fe,Ti)3Al phases can be synthesized after 30 h of high-energy ball milling. In addition, no phase evolution was observed after spark plasma sintering. An analysis of the atomic force microscope images obtained from the nanoindentation tests showed a higher elasticity modulus, higher hardness, and lower plasticity index due to the addition of Ti to the Fe3Al system. (Fe,Ti)3Al displayed better tribological properties as compared with Fe3Al. A smaller volume of the scratched line was clearly seen in the atomic force microscope images of the nanostructured (Fe,Ti)3Al compound. [ABSTRACT FROM AUTHOR]

Friction phenomena in two-dimensional (2D) materials are conventionally studied at atomic length scales in a few layers using low-load techniques. However, the advancement of 2D materials for semiconductor and electronic applications requires an understanding of friction and delamination at a few micrometers length scale and hundreds of layers. To bridge this gap, the present study investigates frictional resistance and delamination mechanisms in 2D tungsten diselenide (WSe 2 ) at 10 µ m length and 100-500 nm depths using an integrated atomic force microscopy (AFM), high-load nanoscratch, and in-situ scanning electron microscopic (SEM) observations. AFM revealed a heterogenous distribution of frictional resistance in a single WSe 2 layer originating from surface ripples, with the mean increasing from 8.7 to 79.1 nN as the imposed force increased from 20 to 80 nN. High-load in-situ nano-scratch tests delineated the role of the individual layers in the mechanism of multi-layer delamination under an SEM. Delamination during scratch consists of stick-slip motion with friction force increasing in each successive slip, manifested as increasing slope of lateral force curves with scratch depth from 10.9 to 13.0 (× 10 3 ) Nm -1 . Delamination is followed by cyclic fracture of WSe 2 layers where the puckering effect results in adherence of layers to the nanoscratch probe, increasing the local maximum of lateral force from 89.3 to 205.6 µ N. This establishment of the interconnectedness between friction in single-layer and delamination at hundreds of layers harbors the potential for utilizing these materials in semiconductor devices with reduced energy losses and enhanced performance., (© 2024 IOP Publishing Ltd.)

The application range of potassium dihydrogen phosphate (KDP) crystals can be expanded by enhancing their surface quality properties. Therefore, a method for controlling the surface-temperature field of various materials was developed to expand the plastic zone to overcome the difficulty in processing KDP crystals. The ductile/brittle transition depth of the KDP crystals was determined using a 38 nm nanoindentation experiment. The nanoscratch experiment revealed the rules of how the transformation depth of the KDP crystals changes with temperatures, and the effect of temperature on the microstructure of the KDP crystals was studied. Finally, KDP crystal surfaces were processed using a UPDFC machine at elevated temperatures. According to our experiments, the surface roughness of the KDP crystal reached 5.275 nm as temperature increased, thus enhancing its surface quality. This method could be applied to other brittle materials.

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]

Nanomechanical definition of the properties of composite specimens based on polylactic acid (PLA) was made in the present study. Research activities with accent on biodegradable polymer nanocomposites have fundamental significance originated from the worldwide plastic waste pollution. To receive hybrid nanocomposites with high level of homogeneity, the low cost and environmentally friendly melt extrusion method has been applied. The role of graphene nanoplatelets (GNPs) and multiwall carbon nanotubes (MWCNTs) as reinforcing nanoparticles dispersed in the polymer matrix was thoroughly investigated. Quasi-static nanoindentation analysis was enriched by performance of accelerated property mapping and nanodynamic mechanical testing in order to fully describe the nanoscale surface homogeneity and stress relaxation behavior of the nanocomposite specimens. That novelty of the research approach had a well-marked contribution over the detection of the new samples' nanomechanical features as a function of the type of carbon nanofiller. Refined nanoscratch experiments uncovered the resistance of the materials against notches by means of measurement of the coefficient of friction and accurate estimation of the residual penetration depth. [ABSTRACT FROM AUTHOR]

• Nanoscratching and MD simulation revealed intricate patterns in Si and GaAs. • Localized amorphization contributed to the suppression of crack formation in Si. • GaAs was prone to cracking despite substantial plastic deformation in comparison to Si. • Ductile-to-brittle transition model had limitations in predicting critical depth of cut. • MD simulation provided insights into atomistic deformation mechanisms in nanogrinding. Ensuring ductile removal in a grinding process is crucial for achieving the desired finish on a hard and brittle single crystal. This study provides new insights into the material removal processes in Si and GaAs single crystals, exploring their deformation behaviour using Berkovich and Conical tips to replicate contact from a fixed abrasive grit. Experimental observations are compared with Molecular Dynamic (MD) simulations to uncover the atomistic deformation mechanisms during the ductile-to-brittle transition (DBT). Notable plastic deformation and minimal cracking were consistently observed in Si, irrespective of the tips used. MD simulations supported this observation, revealing pronounced chip formation indicative of ductile material removal. The resistance to cracking in Si was attributed to amorphization induced by localized high contact stresses. In contrast, GaAs showed a propensity for cracking, with MD simulations revealing dislocation and slip band formation, and cracks emerging in the areas of substantial plastic deformation. These findings address phenomena not previously discernible in experimental studies due to the challenge of real-time observation. Moreover, the tip geometry was shown to significantly influence stress distribution, impacting deformation and crack formation in GaAs. This study also reveals limitations in predicting the critical depth for DBT in both Si and GaAs throught the amended Bifano, Dow, and Scattergood (aBDS) models and MD simulation, offering nuanced insights into these challenges that have not been extensively explored. It was found that the experimental results exceeded predictions by an order of magnitude. These discrepancies underscore the aBDS model's disregard for essential material properties and tip geometry, while the disparities between MD simulation and experiment are primarily attributed to the inherent limitations in the simulated length scales and challenges in detecting initial subsurface cracks. [Display omitted] [ABSTRACT FROM AUTHOR]

• Microstructure effects on nanoscratch behaviors of gold-platinum alloy are revealed. • Hardness and surface quality tend to improve in the [ 1 1 ¯ 0 ] (111) orientation. • Twinning boundary greatly strengthens the plasticity by promoting dislocation nucleation. • Grain boundary or twinning boundary migration contributes to the high removal rate. The microstructural effect on the mechanical behaviors of gold-platinum alloys during nanoscratch is revealed. By adjusting the microstructures (crystallographic orientation, interface type, grain size, twinning thickness), the hardness, plasticity, removal rate and surface roughness of the alloys are significantly improved. The nanoscratch is performed by molecular dynamics (MD). For the single-crystal (SC) alloys, the [ 1 1 ¯ 0 ] (111) -oriented SC alloy shows the high hardness, wear resistance and low roughness. The high dislocation density induces the strong work hardening while the horizontal twinning boundaries (HTBs) effectively improve the surface quality by hindering the elastic recovery. For the bi-crystal (BC) alloys, the BC alloy with TB exhibits the excellent plasticity and low roughness. TB can uniformly limit the dislocation slip and promote the dislocation nucleation to strengthen the plasticity and surface quality. For the polycrystal (PC) and nanotwinned-polycrystal (NTPC) alloys, the alloys with small grain size or small twinning thickness show the high removal rate and low roughness. The reduction in grain size or twinning thickness inhibits the dislocation motion and promotes the GB or TB migration to improve the surface quality and atomic removal. These results provide an important theoretical basis for the microstructural design and nanofabrication of gold-platinum alloys with smooth surface and remarkable mechanical property, expanding the application for the bimetallic materials. [Display omitted] [ABSTRACT FROM AUTHOR]

• 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]

Physical flaws and defects on glass surfaces are known to reduce the mechanical strength and chemical durability of glass. The formation of surface defects depends not only on the mechanical conditions of the physical contact but also on the environment in which the contact is made. In this study, the nanoscratch behavior of soda lime silica (SLS) glass was investigated in 10% and 60% relative humidity (RH) conditions. Based on the evolution of friction and scratch depth, the deformation of SLS glass surface could be divided into four regimes: elastic deformation and recovery (E), RH‐independent mild plastic deformation (P‐1), RH‐dependent intermediate plastic deformation (P‐2), and RH‐independent severe plastic formation (P‐3). It is quite surprising to observe that plastic deformation of the glass surface has dependence on RH of the environment (outside the glass) because plastic deformation is the process occurring below the surface (inside the glass) by the externally applied load. From this result, it can be inferred that frictional energy dissipation mode at the sliding interface, which is a function of adsorbed water molecules, influences the subsurface deformation mode. Although friction, wear, and subsurface deformation/damage are all coupled, there is no direct one‐on‐one correlation among them. [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]

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.

The present work aims to address the effects of the sintering temperature (800–1500 °C) on the mechanical properties and material removal mechanisms of 3 mol% yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP) based on a series of nanoindentation and nanoscratch experiments. The impacts of the sintering temperature on the mechanical properties, including plasticity, deformation behavior, indentation energies, and cracking resistance were rigorously studied. The acquired results indicate that 1100 °C signifies the transition threshold for the ceramic microstructure, leading to the entirely different mechanical properties and indentation responses for materials sintered at temperatures lower or higher than the threshold value. Moreover, 1100 °C is also a transition threshold of the material removal mechanism, before which the material removal mechanism is dominated by the plastic regime, and beyond which, the material removal mechanism tends to show ductile-brittle characteristics. [ABSTRACT FROM AUTHOR]

Current study deals with the effect of carbon nanotube (CNTs) and graphene nanoplatelets (GNPs) reinforcement on the mechanical properties and the adhesion strength of plasma sprayed alumina (Al 2 O 3) single splats, using in-situ picoindentation and nanoscratch test, respectively. The hardness of the Al 2 O 3 splat was measured as 18 ± 5.3 GPa which increased to 34.22 ± 8.44 GPa on 1 wt% CNTs addition and to 42.5 ± 9.06 GPa on 0.5 wt% GNPs addition. Hybrid addition of CNTs and GNPs provided the maximum hardness value of 51.25 ± 8.76 GPa to the Al 2 O 3 splat. Similar trend in the elastic modulus has been reported with a minimum value for Al 2 O 3 splat, i.e. 159 ± 35.40 GPa, and maximum for the Al 2 O 3 splat mixed synergistically with CNTs and GNPs (269 ± 43.12 GPa). Adhesion strength of the Al 2 O 3 splat (0.21 ± 0.11 MPa) also showed a nearly 5-fold increase on hybrid addition of CNTs and GNPs with a maximum value of 1.08 ± 0.38 MPa. This improvement in the properties were due to the extremely high mechanical properties of CNTs and GNPs and better melting of the splats, which not only improved the densification but also provided a better interlocking between the splat and the substrate. [ABSTRACT FROM AUTHOR]

The nanoscratch test has been identified as one of the important tools for evaluating the mechanical and tribological properties of materials. This paper reviews the current researches on the nanoscratch test using to characterise the mechanical properties of three typical materials, including thin film, polymer composite and concrete, from the perspectives of the Berkovich indenter, parameter selection, mode selection, and analysis of resulting data. In addition, to provide a deep understanding on the test from different magnitude, a comparison between the microscratch test and nanoscratch test on the evaluation of tribological performance is also provided in this paper. The characterisation by nanoscratch test of two structural samples, in terms of layered film structures (thin film and coating sample) and single layer block structure (polymer composite sample and concrete samples) are also described in this paper, which aims to provides a deep understand on the evaluation the adhesion, tribological and interfacial properties of the typical materials samples by nanoscratch test. Finally, the coefficient of friction and critical load are discussed, which are two important parameters in tribological properties and adhesion properties.

In this article, the tribological properties of aluminum/MWCNTs/Al2O3sf hybrid composites with varying volume fraction of 10 vol%, 15 vol% and 20 vol% was investigated under dry sliding conditions. The experiments were performed according to design of experiments approach using Taguchi method to predict the wear properties of composites. The results indicated that the composites of 15 vol% had lower wear loss, whereas the coefficient of friction (COF) decreased significantly at 20 vol%. Taguchi based ANOVA analysis showed that the sliding distance was found to be the prominent factor controlling the wear loss; applied load influenced COF most significantly. It could also be noticed that the COF and wear loss increases with an increase in sliding load and sliding distance. The decrease in wear loss and the COF can be attributed to the self-lubrication effect of MWCNTs, and the combined effect of reinforcements in the composites. In addition, nanoscratch test was performed to determine the COF and the effect of the reinforcements on local regions of the composites. The results revealed that higher friction force was obtained near the regions of MWCNTs and Al2O3sf while nanoscratching. The COF of composites of 20 vol% was found to slightly higher compared to that of 10 vol% and 15 vol%. This is attributed to the presence of MWCNTs cluster within the Al2O3sf network results prevent the micro-plastic deformation of Al matrix, and the formation of tribofilms with nanoscaled thickness in the scratch region. These friction and wear results indicate that the presence of a limited amount and size of MWCNTs clusters are beneficial to the tribological properties of the hybrid composites. [ABSTRACT FROM AUTHOR]

In-situ SEM nanoindentation and nanoscratch testing methods are commonly used for mechanical characterization and investigation of the deformation and failure mechanisms of coating materials with micro-to nano-scale thicknesses. However, existing SEM-based integrated nanoindentation and nanoscratch instruments have two main limitations. First, the measured mechanical properties of the coating materials at micro-to nano-scale thicknesses are highly sensitive to surface roughness. Second, the existing SEM-based instruments lack the capability to acquire the morphology of residual imprints in real-time after nanoindentation and nanoscratching. In this study, a novel SEM-based integrated nanoindentation, nanoscratch, and atomic force microscopy (AFM) instrument, namely, NMT-AFM was proposed, developed and fabricated. The self-sensing piezoresistive cantilever (PRC) was selected as the AFM force sensor owing to its miniaturization ability. However, the resistance of the PRC sensor fluctuated because of the electron irradiation from SEM, resulting in the continuous drift of the PRC signal during SEM imaging. To overcome this limitation, a mechanism of PRC signal drift inside SEM was analyzed for the first time, and a PRC signal drift reduction method was proposed based on the mechanism analysis. The experimental results indicated that the PRC signal drift was reduced to 2 nm in 2 min by applied external voltage value U A of 30 V to modified PRC, which proved the proposed mechanism of PRC signal drift during SEM imaging. Finally, the X–Y fine nanopositioner angle calibration test using AFM calibration chip VGRP-UM and the nanoindentation/nanoscratch characterizations of the TiAlSiN coating material were conducted. • The work reports a new piezoresistive cantilever (PRC) signal drift reduction method during SEM imaging. • The PRC signal drift reduction method is based on the proposed P-channel JFET model of PRC during SEM imaging for the first time. • The PRC is chosen as the force sensor of AFM function in NMT-AFM instrument. [ABSTRACT FROM AUTHOR]

The synergistic effect of two carbon nanofillers on the mechanical properties of PLA-based nanocomposites was investigated in the present work. Polylactic acid is relatively brittle semi-crystalline polymer which was selected for composite matrix because of its biodegradable properties. It was reinforced with graphene nanoplatelets and multiwall carbon nanotubes by means of melt mixing preparation method. Nanohardness and Young's modulus of smooth nanocomposite samples received by 3D printing were defined by nanoindentation experiments using Berkovich-type pyramidal nanoindenter. It was found that the compounds, incorporated with both graphene and carbon nanotubes in the polymer structure, exhibit better mechanical performance compared to the nanocomposites loaded with a single carbon nanofiller. Different techniques of sample preparation were applied in order to see the influence of preliminary processing on the nanomechanical properties of composite specimens. X-ray diffraction and Raman spectroscopy were used to study the structural features of the pristine carbon nanomaterials. [ABSTRACT FROM AUTHOR]

Most concurrent multiscale methods that expand atomistic region by continuum domain suffer from inconsistent material constitutive properties, which affect the integrity of model in the interface of atomistic and continuum domains. In this paper, the Generalized Particle (GP) method is employed to simulate nanoindentation and nanoscratching of a single-crystal aluminum sample. The main advantage of the GP method lies in its ability to extend the simulation model while maintaining consistent atomic properties across all scales. Coarsening of the atomic domain has been conducted through two-scale and three-scale GP model. The results showed a strong consistency between the results of full atomic simulations and those achieved through the GP method for both nanoindentation and nanoscratch simulations. Also, wave reflections were not seen at the interfaces. The study revealed that an increase in the number of distinct particle domains led to a reduction in the accuracy of multiscale simulations. [Display omitted] • Nanoindentation simulation of Al by two-scale and three-scale GP method. • Nanoscratch simulation of Al by GP method. • Two-scale and three-scale GP model are compatible with full atom simulations. • Wave reflections were not seen at the interfaces of atomic and particle domains. • More distinct particle domains led to a reduction in the accuracy of GP model. [ABSTRACT FROM AUTHOR]

• The MAEE on the nanomechanical properties of a boroaluminosilicate (BAS) glass series have been discussed. • The MAEE was observed as positive deviations from the linear trend in nanohardness and reduced modulus. • The MAEE manifested as negative deviations from the linear trend in nanoscratch depth, nanoscratch residual depth, nanowear. • The MAEE on nanowear behavior was found to be mainly governed by the nano-indentation and subsurface densification. The mixed alkaline earth effect (MAEE) on the mechanical behavior of oxide glasses have received significant attention of glass scientists. In this study, we unveiled the MAEE on the nanomechanical properties of a boroaluminosilicate (BAS) glass series with the varying molar ratios of R =[MgO]/([MgO]+[CaO]), through a combination of nanoindentation, nanoscratch, and nanowear tests. The MAEE was observed as positive deviations from the linear trend in nanohardness and reduced modulus with varying R. On the contrary, the MAEE manifested as negative deviations from the linear trend in nanoscratch depth, nanoscratch residual depth, nanowear volume, and volume densified by nanowear. The maximum and minimum values were observed at R = 0.56. The MAEE on nanowear behavior was found to be mainly governed by the nano-indentation and subsurface densification. These discoveries provide valuable insights into the nanomechanical properties of glass surfaces, contributing to the development of advanced glasses with improved mechanical properties and extended lifespans. [ABSTRACT FROM AUTHOR]

Nanostructured powder particles of Fe3Al and (Fe,Ti)3Al phases were produced using mechanical alloying. These intermetallic phases with a nearly complete density were consolidated by spark plasma sintering. The mechanical properties of the bulk samples, i.e., elasticity modulus, hardness, and plasticity index, and also their tribological behavior were investigated using nanoindentation and nano-scratch tests. It was found that both Fe3Al and (Fe,Ti)3Al phases can be synthesized after 30 h of high-energy ball milling. In addition, no phase evolution was observed after spark plasma sintering. An analysis of the atomic force microscope images obtained from the nanoindentation tests showed a higher elasticity modulus, higher hardness, and lower plasticity index due to the addition of Ti to the Fe3Al system. (Fe,Ti)3Al displayed better tribological properties as compared with Fe3Al. A smaller volume of the scratched line was clearly seen in the atomic force microscope images of the nanostructured (Fe,Ti)3Al compound.

Abstract This study aims to investigate the gradient nanomechanical behavior of dental fluorosis enamel and provide appropriate selection criteria for restorative materials. The nanomechanical properties of the outer, middle, and inner layers of normal tooth enamel, mild dental fluorosis enamel, and severe dental fluorosis enamel were tested by nanoindentation under an applied load of 2000 μN and holding time of 30 s. The nanotribological properties were then evaluated through nanoscratch tests under an applied load of 1000 μN. In addition, the nanotribological property of the outer layer of dental fluorosis enamel was compared with that of four restorative materials, namely, lithium disilicate glass-ceramic (IPS e.max CAD), polymer-infiltrated-ceramic network (PICN), composite resin block (Lava™ ultimate), and conventional composite resin (Fltek™ Z350XT). The nanohardness and elastic modulus of mild dental fluorosis enamel increased from the outer to the middle layers and then decreased from the middle to the inner layers. By contrast, the changed displacement, friction coefficient, and nanoscratch depth and width decreased from the outer to the middle layers and then increased from the middle to the inner layers. In severe dental fluorosis enamel, nanohardness and elastic modulus increased from the outer to the inner layers, but the changed displacement, friction coefficient, and nanoscratch depth and width decreased from the outer to the inner layers. The nanoscratch depth and width of Lava™ ultimate were similar to those of the outer layer of the mild dental fluorosis enamel. The gradient nanomechanical behavior of dental fluorosis enamel significantly differed from that of normal tooth enamel. Dental materials with a wear resistance similar to that of the opposing enamel are a good choice for restoring dental fluorosis (trial registration: WCHSIRB-D-2014-126, registered 25 December 2014).

Ti–6Al–4V is considered to be the most important and useful alloy in the aerospace industry and many other fields. The growing demand for high productivity in machining requires a novel technique for drilling this material efficiently. In this article, a novel grinding technique for drilling with a combination of ultrasonic-assisted grinding and plasma electrolytic oxidation is proposed. The technique was hence named ultrasonic-assisted plasma oxidation grinding (UPOG). A thin oxidized layer was formed on the surface of the workpiece in the grinding zone by plasma. This could enable a reduction of the expensive grinding wheel, which could lead to environmental friendly machining. The oxidized layer would be much softer than the original material. To reveal its fundamental performance in the drilling of Ti–6Al–4V, experiments were conducted to investigate the effect of ultrasonic vibration on grinding forces and tool wear in the presence of plasma oxidation. To investigate the material removal process for UPOG, nanoindentation and nanoscratch tests were also conducted with plasma oxidation samples. • The drilling processes with ultrasonic vibration and PEO could form an oxide layer. • Chips from the UPEO samples were brittle and more fragile. • This investigation improves the grinding efficiency. • Moreover, various issues related to surface quality can also be solved. [ABSTRACT FROM AUTHOR]