Nanomechanical Behaviors Research Articles

Nanoscale Insights into the Mechanical Behavior of Interfacial Composite Structures between Calcium Silicate Hydrate/Calcium Hydroxide and Silica

The failure of the interfacial transition zone has been identified as the primary cause of damage and deterioration in cement-based materials. To further understand the interfacial failure mechanism, interfacial composite structures between the main hydration products of ordinary Portland cement (OPC), calcium silicate hydrate (CSH) and calcium hydroxide (Ca(OH)2), and silica (SiO2) were constructed while considering their anisotropy. Afterwards, uniaxial tensile tests were conducted using molecular dynamics (MD) simulations. Our results showed that the interfacial zones (IZs) of interfacial composite structures tended to have relatively lower densities than those of the bulk, and the anisotropy of the hydration products had almost no effect on the IZ being a low-density zone. Interfacial composite structures with different configurations exhibited diverse nanomechanical behaviors in terms of their ultimate strength, stress–strain relationship and fracture evaluation. A higher strain rate contributed to a higher ultimate strength and a more prolonged decline in the residual strength. In the interfacial composite structures, both CSH and Ca(OH)2 exhibited ruptures of the Ca-O bond as the primary atomic pair during the tensile process. The plastic damage characteristics of the interfacial composite structures during the tensile process were assessed by analyzing the normalized number of broken Ca-O bonds, which also aligned with the atomic chain break characteristics evident in the per-atom stress map.

Annealing-induced changes in wear resistance and nanomechanical properties of CuZr metallic glass thin films

Over recent years, metallic glass thin films (MGTFs) have found extensive applications in advanced micro-engineering systems. Consequently, there is a need to thoroughly assess the nanomechanical and tribological behaviors of MGTFs to optimize the design of efficient components. In this study, we employed the nanoindentation technique in various modes to investigate the elastic heterogeneity, tribological response, and mechanical properties of CuZr amorphous films. Before conducting the mechanical tests, annealing treatments at 500 K and 600 K were performed to create samples with different stored energies. The thermal history analysis revealed that the annealing process reduced the stored energy in the microstructure. Furthermore, the pre-annealing treatment resulted in increased hardness and Young’s modulus of the thin films. Additionally, higher annealing temperatures significantly improved the wear resistance of the MGTFs. Observing the serration dynamics in the scratching test, we noticed that the annealing treatment induced larger shear bands on the wear track side. Moreover, the increase in annealing temperature led to a reduction in elastic heterogeneity, which was consistent with the enthalpy relaxation values in the samples. This suggests that the annealing temperature enhanced the densely packed atomic structure, leading to the stabilization of the thin films.

Effect of laser-shock peening on the structure and nano-mechanical behavior of a Ti-based metallic glass

As a versatile and nondestructive method, laser-shock peening (LSP) has been extensively utilized to improve the mechanical properties of metallic components. Nevertheless, the underlying mechanism for the LSP-induced structure transformation remains unclear. In this study, the structure and nano-mechanical behaviors of a Ti40Zr25Ni3Cu12Be20 bulk metallic glass (BMG) were investigated before and after LSP processing. The LSP-treated BMG sample remains its amorphous structure. As the laser-beam energy increases, there is a reduction in the local order extent of LSP-treated Ti40Zr25Ni3Cu12Be20 BMGs samples, i.e., an increase in the free-volume contents. A higher free-volume content caused a greater shear-band density for the studied BMG samples, causing a lower nano-hardness. Besides, there exists a gradient in nano-hardness along the LSP direction inside the sample, the nano-hardness increases along the LSP direction (gradually approaching the matrix hardness). This gradient effect can be attributed to the gradual decay of the shock-wave pressure with increasing the depth.

Investigation of upward speed and thickness effects on optical and mechanical properties of hard transparent thin films deposited on polycarbonate substrate

In the present work, nanomechanical behaviors and optical properties of the nanohybrid thin films coated on the polycarbonate (PC) substrates were investigated. Tetraethyl orthosilicate (TEOS), 3-glycidoxypropyl-trimethoxysilane (GPTMS) and aluminum tri sec-butoxide were used as main precursors through very simple and repeatable sol-gel process. Optical, chemical, structural, morphological and mechanical characteristics of the samples were studied by ellipsometry, UV/vis spectroscopy, ATR-FTIR, EDS, XRD, FE-SEM, TEM and nanoindentation-nanoscratch methods. It was found that upward speed had an important effect on the nanomechanical properties while optical properties remained constant. The obtained results indicated that the refractive index of the prepared thin films were significantly lower (1.483) than PC substrate (1.58) led to increase the transmittance that was measured 89 % compared to pristine PC (86 %). Nanohybrid thin films increased PC hardness and elastic modulus to 0.45 and 7.4 GPa respectively at upward speed 5 mm/s. The friction coefficient was decreased to 0.23 and the pencil hardness was 5H at 1887 nm thickness coating at 9 mm/s upward speed.

A comparative study on microstructure, nanomechanical and corrosion behaviors of AlCoCuFeNi high entropy alloys fabricated by selective laser melting and laser metal deposition

• Hierarchically heterogeneous microstructures exist in both SLM- and LMD-processed specimens. • Core-shell FCC precipitates in LMD bear {110} texture at high surface energy and high strain energy. • Hot cracks occurred in both types of specimens due to the incompletely suppressed cu segregation. • A correlation mechanism between microstructure, nano-mechanics, and corrosion behavior was obtained. The present study investigated the microstructure, nanomechanics, and corrosion behavior of AlCoCuFeNi high entropy alloys fabricated by selective laser melting (SLM) and laser metal deposition (LMD). The microstructure of SLM-processed specimens was mainly composed of columnar-grained BCC matrix (∼90 µm in width) and Cu-rich twinned FCC phase. The columnar grains grew epitaxially along the building direction and exhibited a strong {001} texture. In comparison, a coarse columnar-grained BCC matrix (∼150 µm in width) with a stronger 〈001〉 texture, rod-like B2 precipitates, and large core-shell structured FCC phases were formed in the LMD-processed specimens due to the higher heat accumulation effect. Consequently, the LMD-processed specimens showed a lower hardness, wear resistance, and corrosion resistance, but higher creep resistance and reduced Young's modulus than the SLM-processed specimens. Hot cracks occurred in both types of specimens, which could not be completely suppressed due to Cu segregation.

Optimizing mechanical and tribological properties of electrodeposited NiCo alloy coatings by tailoring hierarchical nanostructures

NiCo alloy coatings were prepared via electrochemical deposition on low-carbon steel substrate. These coatings feature hierarchical nanostructures of ultra-fine grains (≈ 200 nm in size) with embedded high density of nano-twins, twin-stacking fault networks and/or martensitic bundle architectures, which were tailored by varying Co content. The nano-mechanical behaviors and dry-sliding tribological properties of the NiCo coatings were systematically investigated. The results reveal that formation of intersecting architectures with nano-twins and stacking faults/martensitic bundles considerably elevates the hardness of the coatings, as the plastic deformation is controlled by the interactions between the dislocations and the interfaces including grain boundaries, twin boundaries and phase boundaries. The presence of the transformation-induced plasticity (TRIP) effect in the dual-phase NiCo coating leads to a deviation from Archard scaling during dry-sliding. The optimized wear resistance exhibited by the dual-phase NiCo coating, corresponding to the lowest wear rate and wear coefficient, was discussed in terms of both the hardness and TRIP effect.

Molecular Dynamics Simulation of Nanoindentation of Nb-Zr Alloys with Different Zr Content

To understand the nanomechanical behaviors of the Nb-based alloys with Zr addition at room/high temperature, the molecular dynamics simulations of nanoindentation are conducted. In this work, the load-unload displacement curve, hardness, and dislocation characteristics of Nb-Zr alloys with varying Zr content ranging from 0 to 5 wt.% are studied. The simulation results are found to closely agree with the experimental one at 1 wt.%, therefore showing the reliability of the simulation. Moreover, considering distinct responses of alloys to different service temperature, the high-temperature nanoindentation are performed. The effects of Zr addition on the mechanical deformation under both temperatures are compared. The same phenomenon is found such that the optimum concentration range yielding the greatest hardness is 1–3 wt.%. The elastic modulus of NbZr alloy improves with elevated concentration at room temperature, while the hardness at higher temperature exhibits the opposite trend. This is attributed to the higher amplitude of atomic vibrations at high temperatures, which is more likely to deviate atoms from their equilibrium positions and weaken the pinning effect under external loading. Therefore, we believe that our studies on the nanomechanical mechanisms of materials at room/high temperature will provide an effective way for the alloying optimization design.

Molecular dynamics simulation of the tensile response and deformation mechanism of diamond/TiC combinations

The diamond materials combine several prominent intrinsic performances, such as high transmittance, low microwave dielectric loss, and so on. A nanoscale carbide layer will be indispensably produced on their surface to guarantee the diamond can be wetted by metallic parts, for example the diamond microwave window for use in thermonuclear fusion reactor. The mechanical performance of the diamond/carbide layer interfacial bonding, which remains unknown because of dimensional limitation, will be critically vital. In this work, molecular dynamics (MD) simulation was conducted to explore the fracture mechanism of diamond/TiC combinations under uniaxial tension. The deformation behavior of (001), (110), and (111) single-crystalline (SC) TiC on diamond was investigated based on the stress–strain curve, fracture process, and dislocation evolution. The crystallographic orientation-dependent fracture modes were revealed. For the case of TiC(001) and TiC(110), the plastic fracture happened. The TiC{111} dislocations would be first emitted from the interface. Different dislocation morphologies were presented, such as stair-rod dislocations and dislocation tangles for TiC(001), as well as geometrically necessary dislocations for TiC(110). For the TiC(111), the brittle fracture took place because most easily activated slip planes were perpendicular to the force direction. Our findings revealed the nanomechanical behaviors and corresponding deformation mechanisms of the diamond/TiC combinations, facilitating the design and development of nanostructured combinations with superior mechanical performance.

Effects of cold-rolling and subsequent annealing on the nano-mechanical and creep behaviors of CrCoNi medium-entropy alloy

The influences of thermomechanical treatment on the microstructural evolution and nano-mechanical behaviors of CrCoNi medium-entropy alloy (MEA) were systematically studied through a series of nanoindentation experiments. Cold-rolling induced substantial grain refinement and during subsequent annealing, the CrCoNi MEA exhibited a highly temperature-dependent recrystallized microstructure characterized by significant variations in grain size, dislocation density, and twin fraction with increasing annealing temperature. The hardness of the cold-rolled sample increased with annealing temperature, reaching its highest value at 600 °C and then decreasing gradually. Annealing was also found to influence the creep behaviors of the CrCoNi MEAs. A cold-rolled sample annealed at 700 °C exhibited the highest resistance to creep. The results of a detailed microstructure examination, calculations, and theoretical analysis revealed that annealing twins play a key role in increasing both the strength and the creep resistance of the CrCoNi MEAs. Short-range order clusters also contributed to the strength and creep resistance.

Effects of Annealing on Enthalpy Recovery and Nanomechanical Behaviors of a La-Based Bulk Metallic Glass

Structural relaxation and nanomechanical behaviors of La65Al14Ni5Co5Cu9.2Ag1.8 bulk metallic glass (BMG) with a low glass transition temperature during annealing have been investigated by calorimetry and nanoindentation measurement. The enthalpy release of this metallic glass is deduced by annealing near glass transition. When annealed below glass transition temperature for 5 min, the recovered enthalpy increases with annealing temperature and reaches the maximum value at 403 K. After annealed in supercooled liquid region, the recovered enthalpy obviously decreases. For a given annealing at 393 K, the relaxation behaviors of La-based BMG can be well described by the Kohlrausch-Williams-Watts (KWW) function. The hardness, Young’s modulus, and serrated flow are sensitive to structural relaxation of this metallic glass, which can be well explained by the theory of solid-like region and liquid-like region. The decrease of ductility and the enhancement of homogeneity can be ascribed to the transformation from liquid-like region into solid-like region and the reduction of the shear transition zone (STZ).

Nanomechanical evaluation of poly (vinylidene fluoride) nanocomposites reinforced with hybrid graphene nanoplatelets and titanium dioxide

This study further enhanced nanomechanical properties of poly (vinylidene fluoride) (PVDF) using hybrid graphene nanoplatelets (GNPs) and titanium dioxide (TiO2) nanopowder. The hybrid nanocomposites were prepared via solution blending and melt-mixing techniques. GNPs and TiO2 nanopowder were surface modified to promote compatibility with the PVDF matrix. Scanning electron microscope (SEM) revealed high degree of dispersion of the nanoparticles in the polymer matrix. The nanomechanical properties were examined using Anton Paar Instrumented Nanoindenter. By incorporation of GNPs-TiO2 hybrid nanoparticles in the matrix, there were increase in nanomechanical behaviors such as hardness, elastic modulus, stiffness and resistance to plastic deformation. For instance, hardness of 3.34wt%GNPs-10wt%TiO2 (115.2 MPa) increased by 79.7% and 17.2% compared to PVDF (64.1 MPa) and 3.34wt%GNPs (98.3 MPa) nanocomposite, respectively. The enhanced properties of the hybrid nanocomposites were due to network strengthening and hardening and restriction of polymer chains mobility offered by rough surfaces of GNPs-TiO2 hybrid nanoparticles.

Coating‐Mediated Nanomechanical Behaviors of CuO Electrodes in Li‐ and Na‐Ion Batteries

AbstractSurface coating strategy has been proved essential for mitigating the large volume change in the electrodes for lithium‐ion batteries (LIBs) and sodium‐ion batteries (SIBs), thus improving the cyclability and working efficiency of batteries. However, the mechanical instability of electrode generated by incorporating heterostructure interface between the coating and core materials remains largely unexplored. Here, the effects of carbon and gold coatings on the nanomechanical properties of CuO nanowires (NWs) are investigated based on the in situ experiments during the electrochemical reactions. It is found that the NW deformability is mediated by the coating materials as well as the reaction speed. Besides, the inhomogeneity between coating and core materials can promote the crack propagation in the lithiated/sodiated CuO/C NWs and sodiated CuO/Au NWs. Further study indicates that the namomechanical behaviors also depend on the different reaction stages, e.g., lithiation/sodiation or delithiation/desodiation. This work serves as a guidance for building better ion batteries not only with improved electrochemical properties but enhanced mechanical stabilities.

Mechanics of Mineralized Collagen Fibrils upon Transient Loads.

Collagen is a key structural protein in the human body, which undergoes mineralization during the formation of hard tissues. Earlier studies have described the mechanical behavior of bone at different scales, highlighting material features across hierarchical structures. Here we present a study that aims to understand the mechanical properties of mineralized collagen fibrils upon tensile/compressive transient loads, investigating how the kinetic energy propagates and it is dissipated at the molecular scale, thus filling a gap of knowledge in this area. These specific features are the mechanisms that nature has developed to passively dissipate stress and prevent structural failures. In addition to the mechanical properties of the mineralized fibrils, we observe distinct nanomechanical behaviors for the two regions (i.e., overlap and gap) of the D-period to highlight the effect of the mineralization. We notice decreasing trends for both wave speeds and Young's moduli over input velocity with a marked strengthening effect in the gap region due to the accumulation of the hydroxyapatite. In contrast, the dissipative behavior is not affected by either loading conditions or the mineral percentage, showing a stronger damping effect upon faster inputs compatible to the bone behavior at the macroscale. Our results offer insights into the dissipative behavior of mineralized collagen composites to design and characterize bioinspired composites for replacement devices (e.g., prostheses for sound transmission or conduction) or optimized structures able to bear transient loads, for example, impact, fatigue, in structural applications.

Nanomechanical Properties of a Bicomponent Epoxy Resin via Blending with Polyaryletherketone

In order to investigate the nanomechanical behaviors and nanotribological properties of bicomponent epoxy resin (BE) blends, which were filled with thermoplastic polyaryletherketone (PAEK) powders, nanoindentation and nanoscratch tests were performed. The brittle fractured morphologies of bicomponent epoxy resin blends were studied. The microhardness and elastic modules of the materials were measured using the nanoindentation technology. The hardness, elastic modulus, and other mechanical properties of materials on a nanoscale were determined. Nanoindentation and scratch experiments showed that the indentation response is dominated by plastic deformation. The microhardness is the lowest as the content of PAEK powders is increased to 30 parts per hundred parts of resin (phr), while that of the neat bicomponent epoxy resin specimen is the highest. Furthermore, the pristine bicomponent epoxy resin (BE) exhibited better load-carrying and indentation recovery capacity than the other three samples. The nanoscratch results indicate that the frictional coefficient of the BE/PAEK-30 blend is the lowest, and while that of the pristine bicomponent epoxy resin is the highest, with better scratch/wear resistance.

Microstructure and nanomechanical properties of Zr-based bulk metallic glass composites fabricated by laser rapid prototyping

In this study, Zr–Al–Ni–Cu bulk metallic glass composites (BMGCs) were successfully fabricated by laser rapid prototyping and systematically characterized using x-ray diffractometry (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicate that the studied BMGCs exhibit periodical microstructure along the deposition direction. According to the microstructural characteristics and phase composition, three identified regions are identified, which are classified as the amorphous zone, NiZr2 nanocrystals + amorphous matrix zone and Cu10Zr7 dendrites + CuZr2 nanocrystals zone. The nanomechanical behaviors were investigated by nanoindentation and nanoscratch tests. The elastic modulus and nanoindentation hardness are in the following order: NiZr2 nanocrystals + amorphous matrix zone > Cu10Zr7 dendrites + CuZr2 nanocrystals zone > amorphous zone. This is mainly attributed to the structural relaxation and crystallization of BMG caused by the effect of heat treatment during the repeated processes of laser heating. Moreover, NiZr2 nanocrystals can effectively inhibit the movement of shear band in amorphous matrix, resulting in the enhancement of their strength and hardness.

Effect of vein microstructure and nanomechanical behaviors on wind-resistant performance of Asian ladybeetle hindwing

Abstract The Asian ladybeetle (Harmonia axyridis) is a high-mobility insect which provides inspirations for Micro-aircraft applications. In this study, the hindwings were cut transversely along the curvature change, then the microstructure of leading main vein was investigated. It was found that the thickness of dorsal side (DS) and ventral side (VS) are different, which has an effect on the flying mechanical behaviors of the beetle. Next, the reduced modulus (Er) and hardness (H) of DS and VS were investigated along the veins varying from the base to the region of the principal transverse fold by using a nanoindenter. Then torque was calculated using ANSYS software and it was confirmed that the vein structure of the hindwing has a relationship to its wind-resistant performance. For further study of the wind resistance performance, two single vein structural models were developed and studied.

Transitions between nanomechanical and continuum mechanical contacts: new insights from liquid structure.

The use of continuum mechanics to describe contacts involving nanoscale and atomic interactions has been one of the key controversies in nanoscience, tribology, and petrophysical and geological studies. By applying a novel nonequilibrium molecular dynamics scheme to wet quartz contacts, this study revealed the key transitions between continuum electrostatic, nanomechanical and Hertzian contact behaviors at around one nm of surface separation, which results in critical contact pressure fluctuations between -30 and 100 MPa. Using a novel liquid-structure analysis scheme based on the spatial distribution of water molecules, the nanomechanical behavior was found to originate from the collapse and localization of layers of water molecules. Moreover, the role of surface curvature on this effect was also quantified and explained based on a new topological descriptor. The findings of this study enrich our understanding of wet contacts and have a wide range of applications from the nanoscale to macroscale.

A Review of Current Development of Graphene Mechanics

Graphene, a two-dimensional carbon in honeycomb crystal with single-atom thickness, possesses extraordinary properties and fascinating applications. Graphene mechanics is very important, as it relates to the integrity and various nanomechanical behaviors including flexing, moving, rotating, vibrating, and even twisting of graphene. The relationship between the strain and stress plays an essential role in graphene mechanics. Strain can dramatically influence the electronic and optical properties, and could be utilized to engineering those properties. Furthermore, graphene with specific kinds of defects exhibit mechanical enhancements and thus the electronic enhancements. In this short review, we focus on the current development of graphene mechanics, including tension and compression, fracture, shearing, bending, friction, and dynamics properties of graphene from both experiments and numerical simulations. We also touch graphene derivatives, including graphane, graphone, graphyne, fluorographene, and graphene oxide, which carve some fancy mechanical properties out from graphene. Our review summarizes the current achievements of graphene mechanics, and then shows the future prospects.

Study on the Nanomechanical and Nanotribological Behaviors of PEEK and CFRPEEK for Biomedical Applications

This study was to investigate the nanomechanical and nanotribological properties of polyether ether ketone (PEEK)-based composites for biomedical applications and to gain a fundamental understanding of the effects of carbon fibers in carbon-fiber-reinforced PEEK (CFRPEEK) on the mechanical properties and wear performance in a microscale. Nanoindentation tests with a Berkovich indenter and nanoscratch experiments with a diamond stylus were performed on PEEK and CFRPEEK samples. The nanowear features and mechanisms of the tested samples were analyzed using 3D white-light interfering profilometry and scanning electron microscopy (SEM). The obtained results indicated that the reinforced carbon fibers increased the nanohardness and elastic modulus and decreased the friction coefficient and wear rate of PEEK. Different to many existing studies where a constant load was used in a nanoscratch test and the normal load was a key factor influencing the scratch performances of the tested specimens, stick–slip phenomena were observed on both PEEK and CFRPEEK in the nanoscratch tests with load increasing progressively. In constant load conditions, it was found that the major nanowear mechanisms of PEEK are adhesion, abrasion, and plastic deformation, while the nanowear mechanisms of CFRPEEK are dominated by severe adhesive wear, abrasive wear and mild fatigue. CFRPEEK has demonstrated superior nanomechanical and nanotribological performances, and hence can be considered a potential candidate for biomedical applications.

Interlayer Coupling Behaviors of Boron Doped Multilayer Graphene

It is fundamentally important to understand how the interlayer interaction of neighboring graphene sheets is influenced by chemical doping. Here we investigate the interlayer coupling of multilayer graphene doped with controlled boron content via the Raman-active in-plane shear mode. The experimental results reveal a remarkable decline in the interlayer shear modulus as boron content increases, which is a direct consequence of the enlarged interlayer spacing, further supported by the molecular dynamic (MD) simulations. Nanoindentation tests were conducted to clarify the influence of interlayer coupling behaviors on nanomechanical behaviors of boron-doped bilayer graphene. As the interlayer slippage is induced under shear deformations, the weakened shear resistance would lead to the reduced energy dissipation during sliding process. Our results provide valuable insight into fundamental mechanical properties of boron-doped graphene and its interfaces and potentially allows tailoring of interlayer coupling f...