Nanoindentation Process Research Articles

Effect of grain size and temperature on mechanical properties of nanocrystalline nickel

Molecular dynamics simulations were employed to perform the nanoindentation analysis of nanocrystalline nickel with polycrystalline crystal structure at different grain sizes and temperatures under an indenter of spherical shape. The results indicate that during the nanoindentation process, dislocations are mainly present near grain boundaries. Atomic rearrangements occur around the indentation area, which leads to the formation of an amorphous region along the grain boundaries. The indentation region contains dislocations and amorphous structures. As the grain size decreases, the indentation stress decreases. However, for grain sizes below 13.7nm, a reverse Hall-Petch relationship is observed between grain size and hardness values. The elastic recovery rate in the depth direction increases with increasing grain size, and is greater than that in the width direction, so the influence of the grain size on the elastic recovery rate in the width direction is very small. At higher simulation temperatures, the load-displacement curve during nanoindentation exhibits significant fluctuations. The higher the simulated temperature, the greater the fluctuation of the load-displacement curve. The hardness values reaches the maximum value at 100K, and then decrease with the increase of temperatures. When the indentation depth remains constant, the number of atoms experiencing higher shear strains increases with increasing temperature.

Molecular dynamics simulation of gradient alloying distribution on the nano-mechanical properties of Nb-Zr alloys

Abstract In this work, a nano-indentation process of homogeneous Nb-Zr alloy and gradient Nb-Zr alloy was simulated using molecular dynamics simulation. The effects of indentation radius, Zr content and system temperature on the mechanical properties and micro-deformation were investigated. The influence of indentation size on nano-indentation experiments was mainly affected by the curvature of the indented part. Comparing the homogeneous and gradient alloys, it was revealed that the gradient alloy had a smoother mechanical performance. The results showed that the effect of Zr content on the hardness of Nb-Zr homogeneous alloy was not linear. The hardness rose, followed by a decline with increasing Zr content, and the turning point came at 1.5 wt%. Under high temperatures, the Nb-Zr homogeneous alloy and gradient alloy layer retained extremely high hardness, exhibiting excellent mechanical properties. Due to the entanglement of multiple dislocations in gradient Nb-Zr alloy at high temperatures, the hardness still increased with increasing temperature at high temperatures. It was worth noting that gradient alloys could disperse stress faster and reach a stable state during the loading process. The hardness of the Nb-Zr homogeneous alloy layer first increased and then decreased as the Zr content changed from 1.0 wt% to 2.0 wt%, as verified by the experiments. This study provided the reference for the preparation of high-temperature applications alloy by constructing Nb-Zr gradient alloy.

Anisotropic Plastic Deformation Mechanism and Indentation Size Effect During Berkovich Nanoindentation Process of ZnSe Crystals in Micro-nanoscale

Anisotropic Plastic Deformation Mechanism and Indentation Size Effect During Berkovich Nanoindentation Process of ZnSe Crystals in Micro-nanoscale

Exploring the effect of layer thickness on the elastoplastic properties of the constituent materials of CrN/CrAlN multilayer coatings: a nanoindentation and finite element-based investigation

This paper aims to assess the effect of layer thickness on the elastoplastic properties of the constituent materials of multilayer coating systems, as well as on the stress and strain fields in the vicinity of the coating/substrate interface. A methodology based on a trust-region reflective optimization algorithm, integrated with finite element analysis of the nanoindentation process, is employed to extract the elastoplastic properties of the distinct layers, constituting multilayer coating. This approach is validated on a CrN/CrAlN multilayer coating systems with varying layer thicknesses from 1 to 0.35 µm, by which Young's modulus (E), yield stress (σy), and work hardening exponent (n) of each individual coating material layer were obtained. The results revealed a reduction in the hardness and Young's modulus of either CrN, or CrAlN coating layer as the layer thickness decreased. Finite element analysis of the nanoindentation process demonstrated that decreasing the coating layer thickness leads to an increase in the plastic deformation within the coatings, which reduces the stress concentration in this area. The simulation results suggest that an optimum thickness of 0.5 μm of CrAlN and CrN monolayer materials would improve the adhesion properties of CrN/CrAlN multilayer coatings.

Molecular Dynamics Investigation of Metastable Structure and Hybridization Bond Evolution in High-Entropy CoCrFeNi Heterostructured Amorphous Carbon Films.

Heterogeneous element doping in amorphous carbon films can reduce residual stresses and improve plastic deformation. Nevertheless, the effects of dopant content and size on the metastable transition mechanism between sp2-C and sp3-C atoms during the deformation process are unclear and difficult to be in situ observed and researched, experimentally. In this work, the mechanical properties and the structural evolution during the nanoindentation of amorphous CoCrFeNi sphere-doped carbon heterostructured films with different radii were simulated. The results indicate that the hardness H and elastic modulus E of the films decreased with the increase of the dopant addition. H decreases from 50.69 to 28.94 GPa, and E decreases from 664.39 to 448.62 GPa. The decrease in the elastic recovery and the enlargement of the shear transition zones indicate that the presence of the amorphous CoCrFeNi dopant can significantly improve the plastic deformation capacity of the films. During the nanoindentation process, the spherical dopants reduce the stress and shear strain of the regions under the indenter in a-C films. The reduction of compressive and shear stresses in the film can inhibit the C atom metastable transition from sp2-C to sp3-C. This can provide a theoretical basis for the development and design of heavy-load and high-deformation-rate a-C films.

Mechanical characterization of Xenopus laevis oocytes using atomic force microscopy

Mechanical properties are essential for the biological activities of cells, and they have been shown to be affected by diseases. Therefore, accurate mechanical characterization is important for studying the cell lifecycle, cell-cell interactions, and disease diagnosis. While the cytoskeleton and actin cortex are typically the primary structural stiffness contributors in most live cells, oocytes possess an additional extracellular layer known as the vitelline membrane (VM), or envelope, which can significantly impact their overall mechanical properties. In this study, we utilized nanoindentation via an atomic force microscope to measure the Young's modulus of Xenopus laevis oocytes at different force setpoints and explored the influence of the VM by conducting measurements on oocytes with the membrane removed. The findings revealed that the removal of VM led to a significant decrease in the apparent Young's modulus of the oocytes, highlighting the pivotal role of the VM as the main structural component responsible for the oocyte's shape and stiffness. Furthermore, the mechanical behavior of VM was investigated through finite element (FE) simulations of the nanoindentation process. FE simulations with the VM Young's modulus in the range 20–60 MPa resulted in force-displacement curves that closely resemble experimental in terms of shape and maximum force for a given indentation depth.

Nanoindentation Response of Structural Self-Healing Epoxy Resin: A Hybrid Experimental-Simulation Approach.

In recent years, self-healing polymers have emerged as a topic of considerable interest owing to their capability to partially restore material properties and thereby extend the product's lifespan. The main purpose of this study is to investigate the nanoindentation response in terms of hardness, reduced modulus, contact depth, and coefficient of friction of a self-healing resin developed for use in aeronautical and aerospace contexts. To achieve this, the bifunctional epoxy precursor underwent tailored functionalization to improve its toughness, facilitating effective compatibilization with a rubber phase dispersed within the host epoxy resin. This approach aimed to highlight the significant impact of the quantity and distribution of rubber domains within the resin on enhancing its mechanical properties. The main results are that pure resin (EP sample) exhibits a higher hardness (about 36.7% more) and reduced modulus (about 7% more), consequently leading to a lower contact depth and coefficient of friction (11.4% less) compared to other formulations that, conversely, are well-suited for preserving damage from mechanical stresses due to their capabilities in absorbing mechanical energy. Furthermore, finite element method (FEM) simulations of the nanoindentation process were conducted. The numerical results were meticulously compared with experimental data, demonstrating good agreement. The simulation study confirms that the EP sample with higher hardness and reduced modulus shows less penetration depth under the same applied load with respect to the other analyzed samples. Values of 877 nm (close to the experimental result of 876.1 nm) and 1010 nm (close to the experimental result of 1008.8 nm) were calculated for EP and the toughened self-healing sample (EP-R-160-T), respectively. The numerical results of the hardness provide a value of 0.42 GPa and 0.32 GPa for EP and EP-R-160-T, respectively, which match the experimental data of 0.41 GPa and 0.30 GPa. This validation of the FEM model underscores its efficacy in predicting the mechanical behavior of nanocomposite materials under nanoindentation. The proposed investigation aims to contribute knowledge and optimization tips about self-healing resins.

Effect of the volume fraction of nanocrystals on the mechanical properties of (Fe0·9Ni0.1)86B14 amorphous/nanocrystalline alloy

The effect of the volume fraction of nanocrystals on the macroscopic mechanical properties and microscopic atomic structure of Fe-based nanocrystalline alloys, as well as the relationship between the two, is an urgent issue to be explored. Seven nanocrystalline alloys with different volume fractions of nanocrystals were formed by annealing treatment of (Fe0·9Ni0.1)86B14 amorphous precursor. Through hardness, flat plate bending, and nanoindentation experiments, it is found that when the volume fraction of nanocrystals reaches the range of 45–55 %, there is an abrupt change in the macroscopic mechanical properties. Specifically, when the volume fraction is less than this range, the properties inherit the amorphous matrix, however, larger than this range, the properties are dominated by precipitated nanocrystalline phases. Meanwhile, based on the molecular dynamics simulation method, seven Fe90Ni10 amorphous nanocrystalline models with different volume fractions of body-centered cubic nanocrystals are established, and the deformation mechanism of models and the evolution of their microstructures during the nanoindentation process are obtained intuitively. Moreover, it is further revealed that the significant changes in the Voronoi polyhedral index, which represents the microscopic atomic structure in this range of nanocrystal volume fractions, are the main reason for the abrupt changes in the mechanical properties at the macroscopic level.

Molecular dynamics analysis of the effect of temperature on the internal structure transformation of polycrystalline 3 C-SiC nanoindentation

To investigate the structure changes of polycrystalline 3 C-SiC nanoindentation process and the influence of temperature effect on its changes, the nanoindentation experiments of polycrystalline 3 C-SiC are constructed by molecular dynamics method. The initial nanoindentation model of polycrystalline 3 C-SiC and diamond indenter is constructed based on the characteristics of Voronoi method in constructing close-packed spatial lattice. The temperature conditions of 300 K, 500 K, 800 K and 1000 K are selected to analyze the dislocation structure, number and length, internal atomic structure, grain boundary structure and deformation degree of polycrystalline 3 C-SiC during nano-indentation process. The stress and deformation of diamond indenter are analyzed. The results show that the higher the temperature, the higher the degree of dislocation stacking. Temperature has an effect on the internal variation of polycrystalline silicon carbide, particularly on the transverse size of the structure. The central force of the diamond becomes weaker and the force on either side becomes stronger. The temperature effect can change the stacking degree of dislocations, reduce the internal structure transformation rate of polycrystalline 3 C-SiC, and transform fewer discrete atoms and increase the number of cubic lattice atoms.

Simultaneous effect of grain size and indenter dimension on the dislocation nucleation and growth in nanoindentation and nanoscratch processes

Simultaneous effect of grain size and indenter dimension on the dislocation nucleation and growth in nanoindentation and nanoscratch processes

Mechanical responses and plastic rheological behavior of Ti–Zr-Hf-Co-Ni-Cu metallic glass thin films deposited with different substrate temperatures during nanoindentation and nanoscratch process

Ti–Zr-Hf-Co-Ni-Cu metallic glass thin films were deposited by magnetron sputtering at different substrate temperatures of 293 K, 373 K, and 473 K. All the thin films were indicated to be amorphous. The roughness was decreased from 0.71 ± 0.02 nm (293 K) to 0.65 ± 0.01 nm (473 K) and the thin film became more densified with fewer voids and defects. Consequently, the mechanical properties, plastic rheological behavior, and nanoscratch properties varied regularly with the microstructure at different substrate temperatures. The hardness and elastic modulus showed increasing trends with the elevated substrate temperature. The strain-rate strengthening effect occurred, causing the gradual disappearance of the pop-in event with the increasing strain rate. The cut-off value of strain burst size showed an increasing trend with the elevating strain rate. This trend was weakened with the elevated substrate temperature due to the decreased chaos of the interaction between atoms. The cut-off value also increased with the elevating substrate temperature. During the nanoscratch measurement, the elastic recovery ratio increased with the elevating substrate temperature. The critical stress for interface separation of the Ti–Zr-Hf-Co-Ni-Cu metallic glass thin film was improved from 1.9 N to 2.7 N with the substrate temperature rising from 293 K to 473 K.

Atomistic understanding of the variable nano-hardness of C-plane sapphire considering the crystal anisotropy

Nanoindentation test method is widely used to measure the material hardness, which is a standard test and the effect of measurement error is limited. However, the measured results of the nano-hardness for the same plane of single crystal materials, such as sapphire, were very different. The possible reason for the difference of nano-hardness is induced by the anisotropy of single crystal materials. In this study, nanoindentation tests were carried out to obtain the nano-hardness of C-plane sapphire. The tests with two different indenter orientations were designed as follow. On C-plane, one edge of the Berkovich indenter was indented parallel to the direction [101‾0], as well as one edge indented perpendicular to the direction [101‾0] for comparison. The average hardness was 25.58 GPa and 29.64 GPa respectively. Molecular dynamics simulation was employed to reveal the generation mechanism of anisotropy in nanoindentation process. The results showed that the distribution of subsurface dislocations and the activation of slip systems were affected by indenter orientations, which resulted in the difference in nano-hardness. When one edge of the Berkovich indenter was indented perpendicular to the direction [101‾0], C-plane sapphire had a stronger ability to resist deformation, showing a higher hardness on the macroscopic level.

Tip-based Lithography with a Sacrificial Layer.

The fabrication of a highly controlled gold (Au) nanohole (NH) array via tip-based lithography is improved by incorporating a sacrificial layer-a tip-crash buffer layer. This inclusion mitigates scratches during the nano-indentation process by employing a 300nm thick poly(methyl methacrylate) layer as a sacrificial layer on top of the Au film. Such a precaution ensures minimal scratches on the Au film, facilitating the creation of sub-50nm Au NHs with a 15nm gap between the Au NHs. The precision of this method exceeds that of fabricating Au NHs without a sacrificial layer. Demonstrating its versatility, this Au NH array is utilized in two distinct applications: as a dry etching mask to form a molybdenum disulfide hole array and as a catalyst in metal-assisted chemical etching, resulting in conical-shaped silicon nanostructures. Additionally, a significant electric field is generated when Au nanoparticles (NPs) are placed within the Au NHs. This effect arises from coupling electromagnetic waves, concentrated by the Au NHs and amplified by the Au NPs. A notable result of this configuration is the enhancement factor of surface-enhanced Raman scattering, which is an order of magnitude greater than that observed with just Au NHs and Au NPs alone.

Molecular dynamics study of the γ/γʹ interface influencing the nano-deformation of nickel-based single crystal alloys during nanoindentation process

Molecular dynamics study of the γ/γʹ interface influencing the nano-deformation of nickel-based single crystal alloys during nanoindentation process

Molecular dynamics for nanoindentation in the γ/α2 interfacial strengthening mechanism of a duplex full lamellar TiAl alloy

To investigate the effect of the γ/α2 interface on the deformation behavior and mechanical properties of the duplex all-sheet TiAl alloy during the nanoindentation process, simulations were carried out using molecular dynamics methods. The mechanical properties, atomic displacements, microscopic deformation behavior, stress-strain, and microstructure evolution patterns during nanoindentation are systematically analyzed. The results show that the movement of the atoms is impeded by the interface, directing them in a direction parallel to the interface and thus increasing the workpiece's resistance to deformation. The γ/α2 interface will prevent the propagation of dislocations, causing dislocation buildup, increasing the strength of the TiAl alloy and acting as a hardening agent. In addition, it has been found that the presence of interfaces impedes the transfer of stress and causes discontinuities in the stress distribution, the closer the region to the interface, the denser the distribution of high-stress strain atoms and the greater the concentration of the stress.

The microstructure evolution of graphene in nanoindentation G/WC-Co based on molecular dynamics simulation

In this paper, nanoindentation processes of graphene nanocoating reinforced cemented carbide (G/WC-Co) is simulated using molecular dynamics method, from which the effect of the relative position of the indenter and Co on the mechanical properties of G/WC-Co is investigated. Visualization techniques are employed to reveal the microstructure evolutionary behavior of graphene during the nanoindentation process. The results show that the loading force of cemented carbide with graphene nanocoating during nanoindentation is 18.2050 μN, which is 135.47 % higher compared to 7.7312 μN, the loading force of bare cemented carbide. At a nanoindentation of 8.3 Å, sp3 bond increases sharply in graphene, which results in the transformation of graphene into diamond-like carbon (DLC). The simulation results indicate that at the beginning of nanoindentation, the substrate exhibits significant loading resistance due to the high shear modulus of graphene itself. With the further development of nanoindentation, graphene ruptures, and part of graphene evolves to form DLC film, which enhances mechanical property of cemented carbide substrate.

Designing a Compact High-precision Positioner with Large Stroke Capability for Nanoindentation Devices

A new design of a fine positioner or high precision driven unit with a large positioning range is proposed for a custom-made in-situ indenter device equipped inside an SEM chamber. The design configuration of the proposed system is size-effective for the confined working area of the SEM chamber. The indentation depths can be precisely varied by controlling the fine positioner driven by a piezoelectric actuator. The main goal is to achieve very deep penetrations toward the bottom layers of tall or large-size scale specimens by single indentation, without the need for sequential indentations. Thus, the proposed design can eliminate the need for sequential adjustments of the specimen position with respect to the indenter tip as currently being practiced by the researchers. The specimen position adjustment after each indentation heavily depends on the coarse positioner and its accuracy level in a sub-millimeter regime which could result in position errors and unwanted lateral forces in the nanoindentation process. Therefore, the sequential indentations technique could lead to considerable variations in the outcomes of nanoindentation tests done on similar specimens. The proposed design will be realized to deploy in the Continuous Stiffness Measurement (CSM) techniques generally used to evaluate elastic properties as a function of continuous penetration depth with high-frequency loading and unloading cycles.

Investigation of deformation mechanism of SiC–CuNi composite thin film material nanochannels by molecular dynamics simulation

Semiconductor–metal composites are widely used in aerospace and automotive manufacturing, weapon production, and electronic packaging because of their high hardness and strength as well as low coefficient of thermal expansion. In this study, SiC–CuNi composite films produced by single-target and dual-target co-deposition were simulated using molecular dynamics. The films were subjected to high-temperature quenching to obtain an annealing model. The deformation behaviors of the deposition and annealing models during the nanoindentation process were investigated in detail. Then, a characterization method for inspecting the roundness of nanochannels was proposed. In the deposition model, the Ni–Cu model generated amorphous structures at the interface. However, the annealing treatment atomically rearranged the film, producing dense films with improved crystalline quality. Other deposition models are developed using complex twin structures, which play a role in stress distribution and strain diffusion during deformation. Comparative investigation shows that high-temperature quenching can effectively enhance the stiffness of composite films, tightly bonding the atoms at the semiconductor–metal interface. Hardness calculations were performed for all models and the result was that the Cu + Ni model had the highest hardness. Moreover, the formation of nanochannels is affected: the tighter the bond, the more uniform the nanochannels.

Grain refinement induced by grain boundary segregation in FeNiCrCoCu high-entropy alloys using molecular dynamics simulation of nanoindentation

Atomistic simulation of nanoindentation is performed to investigate the effect of Cu segregation at grain boundaries (GBs) on the mechanical properties of FeNiCrCoCu high-entropy alloys. Initially, a combined Monte Carlo and Molecular dynamics simulation technique is adopted to generate the models with Cu segregation, and further the cases of random Cu distribution are considered for the purpose of comparision. The dislocation density, shear strain and GB behavior in the process of nanoindentation are analyzed in detail. The results reveal that the Cu segregation at GBs leads to superiority in hardness, strength, and stiffness. Dislocation analysis shows that the sessile dislocation density is higher at the initial state for the segregation sample, while dislocation nucleation and movements are suppressed so that dislocation-mediated plasticity is weakened. Furthermore, microrotation analysis during the nanoindentation process indicates that segregation of Cu pins the GBs, thereby inhibiting GB rotation and consequently weakening GB-mediated plastic deformation. In this case, grain refinement is observed, and in good agreement with experiment results. Overall, this study provides insights into the influence of GB segregation of Cu on the mechanical properties and deformation response of FeNiCrCoCu HEAs, and highlights the importance of GB composition for tailoring high-strength materials.

Martensite Variant Identification Method for shape memory alloys by using graph neural network

Detailed microstructure evolution in shape memory alloys (SMAs) can be studied by molecular dynamics (MD) simulations. However, the conventional post-processing methods for atomistic calculations, such as Common Neighbor Analysis (CNA), fail to identify distinct crystal variants and to reveal twin alignments in SMAs. In the current work, a powerful and efficient post-processing tool based on GraphSAGE neural network is developed, which can identify multiple phases in martensitic transformation, including the orthorhombic, monoclinic and R phases. The model was trained by the results of sets of temperature- and stress-induced martensitic transformation MD calculations. The accuracy and generality were also verified by the application to the cases which did not appear in the training dataset, such as the unrecoverable nanoindentation process. The proposed method is rapid, accurate, and ready to be integrated with any visualization tool for MD simulations. The outcome of the current work is expected to accelerate the pace of atomistic studies on SMAs and related materials.