Nanoindentation Method Research Articles

Nanogranular nature of the CSH gel

Hydration of cementitious materials is accompanied by the formation of calcium hydrosilicates (CSH). Accordingly, the hydration process is completed in the early, middle and late periods, leading to the formation of two types of CSH phases: low density (LD) and high density (HD). Using the nanoindentation method, it was explained nanogranular nature of the CSH gel, which is due to the contact forces of the CSH gel particles for these phases.

Strength and stiffness characterization of ultra-high performance concrete (UHPC) cement paste phases through in-situ micro-mechanical testing

Compressive strength and stiffness of concrete materials involve the complex interaction of aggregates and hardened cement, which can involve even more complex phases formed through hydration processes. Typically, the strength and stiffness of concrete materials are determined through material-scale testing, focusing on the bulk behavior while ignoring individual constitutive material interactions. This study aims to identify individual cement phase contributions to bulk concrete properties through the characterization of individual hardened cement-paste phases using micro-scale compressive testing. In this study, in-situ micro-compression measurements are used to generate statistical distributions of compressive strength and stiffness for five hardened cement phases and one phase composite. Results from the in-situ micro-compression testing indicate that AFt/AFm and CH/C–S–H micropillars exhibit higher stiffness and strength when compared to hardened C–S–H and C-A-S-H phases. Comparing measured micropillar strength and stiffness values with traditional nano-indentation methods indicates that nano-indentation approaches may provide a higher estimation of individual phase stiffness due to material confinement boundary effects.

Control of fracture toughness of kerogen on artificially-matured shale samples: An energy-based nanoindentation analysis

Understanding controls on mechanical properties of organic-rich shale is essential in exploration and successful production from hydrocarbon reservoirs. In previous works, most researchers have focused on the influence of thermal maturity and organic type on elastic and viscoelastic properties of organic matter. However, fracture toughness, an important parameter in engineering design, has been less investigated. In this study, shale samples with different thermal maturity were obtained by programmed heating. Then, the fracture toughness of organic matter in shale samples was measured using an energy-based nanoindentation method, and the influence of geochemical features was determined. Organic matter was classified as inertinite, vitrinite and bitumen, and the fracture toughness of tested organic matter was in the range of 0.023–0.081 MPa*m0.5. The results indicated that the fracture toughness of vitrinite increased with thermal maturity. Additionally, both the reduced modulus of vitrinite and bitumen increased, while the viscosity of all types of organic matter decreased, with higher levels of thermal maturity. Moreover, a comparison between mechanical parameters of artificially-matured samples, and those of natural samples, was conducted. The fracture toughness of organic matter obtained in this study is crucial for parameter estimation of fracture propagation and homogenization models.

Mechanical Response of Cu/Sn58Bi-xNi/Cu Micro Solder Joint with High Temperatures

Sn58Bi solder is considered a promising lead-free solder that meets the performance requirements, with the advantages of good wettability and low cost. However, the low melting point characteristic of Sn58Bi poses a serious threat to the high-temperature reliability of electronic products. In this study, Sn58Bi solder alloy based on nickel (Ni) functionalization was successfully synthesized, and the effect of a small amount of Ni on creep properties and hardness of Cu/Sn58Bi/Cu micro solder joints at different temperatures (25 °C, 50 °C, 75 °C, 100 °C) was investigated using a nanoindentation method. The results indicate that the nanoindentation depth of micro solder joints exhibits a non-monotonic trend with increasing Ni content at different temperatures, and the slope of the indentation stage curve decreases at 100 °C, showing that the micro solder joints undergo high levels of softening. According to the observation of indentation morphology, Ni doping can reduce the indentation area and accumulation around the indentation, especially at 75 °C and 100 °C. In addition, due to the severe creep phenomenon at 100 °C, the indentation hardness rapidly decreases. The indentation hardness values of micro solder joints of Cu/Sn58Bi/Cu, Cu/Sn58Bi-0.1Ni/Cu, and Cu/Sn58Bi-0.2Ni/Cu at 100 °C are 14.67 ± 2.00 MPa, 21.05 ± 2.00 MPa, and 20.13 ± 2.10 MPa, respectively. Nevertheless, under the same temperature test conditions, the addition of Ni elements can improve the high-temperature creep resistance and hardness of Cu/Sn58Bi/Cu micro solder joints.

Elastic properties and tensile strength of 2D Ti3C2Tx MXene monolayers

Two-dimensional (2D) transition metal nitrides and carbides (MXenes), represented by Ti3C2Tx, have broad applications in flexible electronics, electromechanical devices, and structural membranes due to their unique physical and chemical properties. Despite the Young’s modulus of 2D Ti3C2Tx has been theoretically predicted to be 0.502 TPa, which has not been experimentally confirmed so far due to the measurement is extremely restricted. Here, by optimizing the sample preparation, cutting, and transfer protocols, we perform the direct in-situ tensile tests on monolayer Ti3C2Tx nanosheets using nanomechanical push-to-pull equipment under a scanning electron microscope. The effective Young’s modulus is 0.484 ± 0.013 TPa, which is much closer to the theoretical value of 0.502 TPa than the previously reported 0.33 TPa by the disputed nanoindentation method, and the measured elastic stiffness is ~948 N/m. Moreover, during the process of tensile loading, the monolayer Ti3C2Tx shows an average elastic strain of ~3.2% and a tensile strength as large as ~15.4 GPa. This work corrects the previous reports by nanoindentation method and demonstrates that the Ti3C2Tx indeed keeps immense potential for broad range of applications.

Multi-scale characterization and analysis of cellular viscoelastic mechanical phenotypes by atomic force microscopy.

The viscoelasticity of cells serves as a biomarker that reveals changes induced by malignant transformation, which aids the cytological examinations. However, differences in the measurement methods and parameters have prevented the consistent and effective characterization of the viscoelastic phenotype of cells. To address this issue, nanomechanical indentation experiments were conducted using an atomic force microscope (AFM). Multiple indentation methods were applied, and the indentation parameters were gradually varied to measure the viscoelasticity of normal liver cells and cancerous liver cells to create a database. This database was employed to train machine-learning algorithms in order to analyze the differences in the viscoelasticity of different types of cells and as well as to identify the optimal measurement methods and parameters. These findings indicated that the measurement speed significantly influenced viscoelasticity and that the classification difference between the two cell types was most evident at 5 μm/s. In addition, the precision and the area under the receiver operating characteristic curve were comparatively analyzed for various widely employed machine-learning algorithms. Unlike previous studies, this research validated the effectiveness of measurement parameters and methods with the assistance of machine-learning algorithms. Furthermore, the results confirmed that the viscoelasticity obtained from the multiparameter indentation measurement could be effectively used for cell classification. RESEARCH HIGHLIGHTS: This study aimed to analyze the viscoelasticity of liver cancer cells and liver cells. Different nano-indentation methods and parameters were used to measure the viscoelasticity of the two kinds of cells. The neural network algorithm was used to reverse analyze the dataset, and the methods and parameters for accurate classification and identification of cells are successfully found.

Determination of fracture toughness of the thin diamond-like coatings by nanoindentation

The results of a study of the structure and physical and mechanical properties of diamond-like coatings (DLC) on sublayers of different hardness are presented. The coatings have high hardness, but at the same time they are prone to delamination and destruction due to high residual internal stresses. The fracture toughness was determined by the nanoindentation method and the energy calculation method using approach-retraction curves. Atomic force microscopy was used to study the surface structure and deformation region after nanoindentation. A change in the surface structure and roughness of DLC was established depending on the sublayer. Low roughness is characteristic of DLC on a copper sublayer. Applying а titanium sublayer leads to an increase in the elastic modulus of the DLC. The microhardness of both coatings is practically the same. AFM studies have shown two different types of DLC deformation after nanoindentation with a Berkovich pyramid. A crack on coatings with a copper sublayer propagates around the indentation print, and on an DLC with a titanium sublayer, it propagates along the edges of the indentation. It was found that the fracture toughness of DLC on a Ti sublayer is 33 % lower compared to DLC on a Cu sublayer due to a decrease in stress relaxation inside the coating. The considered coatings can be used in microelectronics for protection against mechanical damage on contacting and rubbing surfaces.

К вопросу определения точки контакта в силовых измерениях методами атомно-силовой микроскопии

Atomic force microscopy (AFM) is a widely used technique for obtaining information about the three-dimensional structure and physical and mechanical properties of surfaces. In nanoindentation methods, an AFM probe is brought to the sample from a distance and then interacts with the surface. Accurate determination of the point of contact of the probe tip with the surface in these measurements is necessary for reliable calculation of both the non-contact interaction constants and the structural and mechanical properties of the material. The tip-surface contact is preceded by a rapid jump of the probe to the surface due to attractive forces in experiments conducted in ambient conditions. If the stiffness of the probe beam or the sample does not allow the probe to deform the surface, then the end of the probe jump (minimum deflection of the beam as the probe approaches the material) is usually taken as the start of the contact. If the surface is soft enough, contact may occur earlier than the end of the rapid jump, i.e., the tip will begin to penetrate into the surface before the jump is complete. In this work it is shown that the contact of the tip with a deformable polymer surface occurs before the completion of the jump of the tip to the surface. It is reasonable to take the point corresponding to the maximum change in the beam deflection as the beginning of the contact between the probe and the material. The significant speed of the approach of the tip to the surface under the action of attractive forces leads to a loss of experimental data in the section of the curve near the transition from non-contact to contact interaction. Insufficient rate of data capture and high approach velocity can cause significant points of the force curve to be missed, i.e., lead to errors in determining the beginning of the contact both for soft and hard surfaces.

Investigation of grain size and geometrically necessary dislocation density dependence of flow stress in Mg-4Al by using nanoindentation

Models for grain size dependence of flow stress typically ignore contributions from geometrically necessary dislocations (GNDs) in the grain boundary regions. Ashby had proposed the following equation for flow stress (τ) as a function of grain size (d) and effective plastic strain (ε¯): τ=τ0+C′Gbε¯d using an unknown empirical coefficient, C’, In this study, the coefficient, C’, and equation for the grain size dependence of flow stress were investigated in Mg-4Al using nanoindentation. C’ ranges from 1.4 to 7.11 that is related to the hardness difference (∆H0) between the adjacent grains as C′=0.62ΔH0. Ashby equation was used to predict uniaxial stress-strain curves in grain sizes of 55 µm, 187 µm, and 333 µm. The results showed lower flow stress and lower hardening rate compared to experimentally measured tensile stress-strain response. The discrepancy seems to be a result of hardening effect of SSDs. We propose a modified Ashby equation that takes into account the hardening effect of SSDs and GNDs separately, resulting in a better agreement between calculated and experimentally measured values. This analysis demonstrates estimation of uniaxial stress-strain response using nanoindentation measurements that captures effects of grain size, and strain hardening from SSDs and GNDs. The combination of the revised equation and nanoindentation method will enable rapid exploration of stress-strain response of a diverse range of single-phase polycrystalline alloys.

Investigation of silicon carbon oxynitride thin film deposited by RF magnetron sputtering

In this research, silicon carbon oxynitride (SiCON) thin films were deposited on silicon substrate by a radio frequency magnetron sputtering method. The effect of methane reactive gas flow rate on the structural, morphological, optical, and mechanical properties of the thin films was evaluated by using of grazing incidence X-ray diffraction (GIXRD), Raman spectroscopy, attenuated total reflectance-fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) , field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), fourier transform infrared spectroscopy (FTIR), ellipsometry and nano-indentation methods. The results of the GIXRD proved the formation of an amorphous structure in the thin films. Also, the Raman spectroscopy results determined the absence of graphite nanocrystals in the thin film structure. FE-SEM revealed the formation of a thin film with a smooth, dense and crack-free surface. AFM results showed that SiCON thin film is formed with very low surface roughness in the RMS range of 0.73 nm to 4.39 nm. The results of the ellipsometry analysis indicated that the refractive index of the thin film was changed during increase of the CH4 reactive gas flow rate in the of 1.4 to 1.61 at 4 µm. According to the nano-indentation results, sample N10-C20-R1 has the highest hardness and Young's modulus equals 22.7 GPa and 231.6 GPa, respectively.

Phase-Modulated Elastic Properties of 2D Magnetic FeTe: Hexagonal and Tetragonal Polymorphs.

2D layered magnets, such as iron chalcogenides, have emerged these years as a new family of unconventional superconductors and provided the key insights to understand the phonon-electron interaction and pairing mechanism. Their mechanical properties are of strategic importance for the potential applications in spintronics and optoelectronics. However, there is still a lack of efficient approach to tune the elastic modulus despite the extensive studies. Herein, the modulated elastic modulus of 2D magnetic FeTe and its thickness-dependence is reported via phase engineering. The grown 2D FeTe by chemical vapor deposition can present various polymorphs, that is tetragonal FeTe (t-FeTe, antiferromagnetic) and hexagonal FeTe (h-FeTe, ferromagnetic). The measured Young's modulus of t-FeTe by nanoindentation method shows an obvious thickness-dependence, from 290.9±9.2 to 113.0±8.7 GPa when the thicknesses increased from 13.2 to 42.5 nm, respectively. In comparison, the elastic modulus of h-FeTe remains unchanged. These results can shed light on the efficient modulation of mechanical properties of 2D magnetic materials and pave the avenues for their practical applications in nanodevices.

Biocompatibility screening of Mo–Si–Ta glassy alloy films sputtered on additive manufactured Ti–6Al–4V implant prototypes and PCL scaffolds

A ternary system of amorphous alloy with the components Mo, Ti, and Si with the composition Mo54Si33Ta13 has been chosen as the surface coating for the implantable materials to improve Ti6Al4V bioactivity. Ti6Al4V alloy metal powders were used to create the implant prototypes with the 3D metal printer. With the aid of a DC magnetron, the films are sputtered onto the implant prototypes. Elemental composition, amorphous nature, surface chemistry and topography of the as-fabricated microstructure films were comprehensively analysed using X-ray diffraction analysis, X-ray photoelectron spectroscopy and electron/atomic force microscopic techniques. The mechanical properties were studied from Nano indentation method. The coatings were confirmed to be cytocompatible determined from the in-vitro biocompatibility investigations using human osteosarcoma cells. The electrochemical corrosion studies carried out in SBF showed the higher corrosion resistance for the thin film metallic glass (TFMG)-coated customized 3D printed Ti-alloy implants than the pristine specimen.

Novel nanoindentation strain rate sweep method for continuously investigating the strain rate sensitivity of materials at the nanoscale

We introduce a new nanoindentation method to continuously measure the hardness while sweeping through orders of magnitudes of strain rates within a single experiment. While nanoindentation already allows the determination of the strain rate sensitivity of materials by means of strain rate jump tests, these are typically limited to few discrete strain rates. With the new method, the strain rate sensitivity can be measured continuously as a function of the strain rate. Applications to fused silica, Zn-22 %Al superplastic alloy, single crystalline aluminum, various nanocrystalline metals and a palladium-based metallic glass are shown. Besides some discrepancy with the reference measurements, the new method seems only affected by the presence of a strong nanoindentation size effect. Provided this indentation size effect is not excessively large and can be corrected for accurately, the method proves robust, with no suggestion that the direction of the strain rate sweep affects the evaluation of the strain rate sensitivity.

A different attempt to investigate the influence of PTA parameters on microstructure evolution and mechanical characteristics of nickel base powder (Ni-WC) deposited tool steel

The impact of joining parameters, namely preheat, current, and travel speed, due to the crack formation susceptibility of D2 steel during the deposition process, is crucial to achieve weld bead geometries with acceptable metallurgical and mechanical properties. Therefore, the main purpose of the current article is to optimize welding parameters to obtain a sufficient hardfaced coating of nickel-base powder combined with tungsten carbide on the tool steel by the plasma transferred arc (PTA) process with the help of the Design of Experiment (DoE) method. To analyze the properties of the welding beads, scanning electron microscopy (SEM) accompanied by EDS, optical microscopy (OM), XRD analysis, microhardness, and nano-indentation methods on the samples were applied. The results indicated that there is adequate adhesion and continuous bonding between areas due to improved interactions between hard particles and matrix which leads to a reduction in the porosity of the composite coatings. According to the obtained results, the optimized parameters (current, travel speed, and preheating temperature) for uniform distribution of reinforcing particles and high mechanical properties are 86 A, 85 cm/min, and 1350 °C, respectively. Based on optical profilometry analysis on the surface of the samples, there is high homogeneity in reinforcing distribution. The nanoindentation analysis detected three prominent phases, including FeNiCr dendritic matrix phase, large WCrC (carbide) phase, and mono tungsten carbide WC phase. The obtained results improve the length of the tool's service life and an economic fabrication with decreased unit costs.

Effect of ion-induced secondary radiations on the formation of extended defects and radiolysis beyond the range of swift 12C, 50Ti, and 52Cr ions in LiF

The objective of this research is to study the role of ion-induced secondary radiations on structural damage in LiF crystals irradiated with ∼ 10 MeV/u energy 12C, 50Ti, and 52Cr ions using experimental methods of nanoindentation, Atomic Force Microscopy, optical absorption, depth-resolved photoluminescence and chemical etching. In LiF crystals irradiated at room temperature with 50Ti and 52Cr ions, the chemical etching method revealed formation of nano-sized colloids in a wide area (up to one mm) beyond the ion penetration depth. Annealing experiments on irradiated samples at temperatures above 620 K, show enhanced manifestations of radiolysis in ion-irradiated and beyond-range areas accompanied by the emission of radiolysis residues. The multicomponent secondary radiation following the ion-induced inelastic nuclear reactions is discussed as the plausible mechanism of the observed long-range damage.

Mechanical Analysis and Constitutive Modeling of Nonlinear Behavior of Silver-based Conductive Ink

Stretchable electronic devices are progressively deployed in many applications of mechanical, electrical, and bio-medical engineering. These circuits are made of stretchable and flexible substrate, as well as conductive ink, and various electronic components. The choice of components and layouts for the substrate and conductive ink can regulate the stretchability of stretchable circuits. On top of that, the substance utilized to create the conductive ink must have high electrical conductivity and strong adherence to the substrate in order to produce a high-quality stretchable printed circuit. Thus, this study focused on the development of stretchable conductive ink using silver powder as a conductive filler and PDMS-OH as a binder. The mechanical properties of the synthesized ink were investigated via simple uniaxial tensile testing method and nanoindentation technique, respectively. Accordingly, the modulus of elasticity, tensile stress and yield stress of the ink were obtained as 5.72 MPa, 1.195 MPa, and 0.86 MPa, congruently at 137% strain before undergoing failure. The experimental stress-strain data was then employed on the elastic-plastic constitutive model to investigate the elastomeric properties of the ink as it is an alternative method of lengthy and expensive procedures of validating different polymers. Moreover, the hardness and reduced modulus of the ink were evaluated by nanoindentation method using 5 mN maximum load with 0.5 mN/s loading/unloading rate and 2 secs holding time. Consequently, the hardness and reduced modulus values were obtained as 1.45 MPa and 34.53 MPa, respectively. These values were further validated by Oliver-Pharr method, and were in a good agreement.

Fabrication process optimization of nHA–CNTs-reinforced PEEK hybrid nanocomposite

Compression molding is the leading fabrication process for polymer composites. The settings of process parameters highly influence the mechanical properties of composites. This study optimized the ball-mixing and compression-molding process parameters for the fabrication of hybrid nanocomposites based on polyetheretherketone (PEEK), multiwalled carbon nanotubes (MWCNTs) and nano-hydroxyapatite using the Taguchi method. The elastic modulus examined using the nanoindentation method of static mechanical analysis was taken as the output response variable. The optimum levels of mixing time, mold temperature, mold pressure and holding time process parameters for the maximum elastic modulus were found to be 90 min, 400°C, 150 bar and 15 min, respectively. The analysis of variance technique showed that the mold temperature had the highest contribution (46.82%) in enhancing the elastic modulus to the largest value. The elastic modulus and hardness of the PEEK-based hybrid nanocomposite with 30 wt.% nHA and 3 wt.% MWCNTs were observed to be 83 and 65% higher than those of pure PEEK, respectively. The hydrophilicity of PEEK was improved with the reinforcement of nHA, attributed to the presence of oxygen-containing functional groups in the chemical structure of nHA.

A New Elementary Method for Determining the Tip Radius and Young's Modulus in AFM Spherical Indentations.

Atomic force microscopy (AFM) is a powerful tool for characterizing biological materials at the nanoscale utilizing the AFM nanoindentation method. When testing biological materials, spherical indenters are typically employed to reduce the possibility of damaging the sample. The accuracy of determining Young's modulus depends, among other factors, on the calibration of the indenter, i.e., the determination of the tip radius. This paper demonstrates that the tip radius can be approximately calculated using a single force-indentation curve on an unknown, soft sample without performing any additional experimental calibration process. The proposed method is based on plotting a tangent line on the force indentation curve at the maximum indentation depth. Subsequently, using equations that relate the applied force, maximum indentation depth, and the tip radius, the calculation of the tip radius becomes trivial. It is significant to note that the method requires only a single force-indentation curve and does not necessitate knowledge of the sample's Young's modulus. Consequently, the determination of both the sample's Young's modulus and the tip radius can be performed simultaneously. Thus, the experimental effort is significantly reduced. The method was tested on 80 force-indentation curves obtained on an agarose gel, and the results were accurate.

Measurement of Creep Stress Exponent of TC17 Titanium Alloy by Nanoindentation Method at Room Temperature.

The creep stress exponent is commonly employed to characterize the deformation mechanism during the steady-state creep stage, serving as an indicator of creep behavior. The creep phenomenon of high melting point metallic materials is not obvious at room temperature. However, the nanoindentation method proves suitable for investigating the creep properties of metallic materials under such conditions. Consequently, this paper places emphasis on measuring the creep stress exponent of TC17 titanium alloy at room temperature using the load preservation stage of the nanoindentation method with a constant loading rate. In order to investigate the effects of loading rate and maximum load on the experimental results, different loading rates were applied to the diamond Berkovich indenter to reach different maximum loads. The indenter was held under the maximum load for a duration of 360 s, and the relationship between the indentation strain rate and indentation stress during the holding process was used to obtain the creep stress exponent of the material at room temperature. The findings indicate that within the loading rate range of 1.25 to 15 mN/s and maximum load range of 50 to 300 mN, the influence on the experimental results is insignificant. Ultimately, the distribution range of the creep stress exponent for TC17 titanium alloy at room temperature was measured to be 8.524-8.687.

Research on the influence of single-crystal germanium cutting parameters based on molecular dynamics

As a metalloid with unique properties, single crystal germanium is widely used in semiconductors, infrared optics, and other fields. To ensure the processing accuracy of single-crystal germanium, it is necessary to optimise the selection of parameters during processing. This paper uses molecular dynamics methods to study the cutting process of single-crystal germanium with the cutting depth and cutting speed as parameters and uses nanoindentation method to test the mechanical properties of the processed single-crystal germanium surface. The study found that with the increase of cutting depth, the cutting force and cutting heat increased significantly, the depth of the deformed layer increased significantly, and the stiffness of single-crystal germanium decreased significantly; with the increase of cutting speed, there was no built-up edge Influence, the cutting force is reduced, and more cutting heat is generated, and the depth of the deformation layer is higher, and the HCP structure increases, but the cutting speed has no obvious relationship with the mechanical properties of the machined surface.