Nanoindentation Results Research Articles

Microstructure correlation in high-strength steels with continuous stiffness mode nanoindentation results. High-resolution vs. low-resolution nanoindentation

AbstractThis study utilizes instrumented nanoindentation to compare the mechanical response of a transformation-induced plasticity (TRIP) steel to that of a quench and partition steel (QP). The nanoindenter was operated using continuous stiffness mode, and the microstructure under the indent revealed by chemical etching was examined. Examination of the microstructure in the indents by scanning electron microscopy allows a direct correlation with nanoindentation properties. It is found that the hardness measured at an indentation depth of 1.1 μm is, on average, significantly greater in the QP steel than in the TRIP steel. The continuous hardness measurement also allows the microstructure observed at the center of the indent to be correlated with the hardness values when indentation depths are <0.1 μm. This high-resolution hardness measurement allows for a direct comparison of mechanical response for the individual retained austenite phase particles in the TRIP steel with the strengthening microconstituent in the QP steel. With this methodology, the surprising result is that the TRIP retained austenite particles have a higher hardness than the QP hardening microconstituent. It is proposed that the resolution of the apparent disagreement between the hardness measurements obtained at 1.1 μm depth (QP has the higher hardness) and the 0.1-μm depth hardness measurements of the microconstituents containing retained austenite (TRIP has the higher hardness) lies in the volume fraction of the microconstituent as the QP has a two- to threefold higher volume fraction of hardening phase as compared to TRIP.

Surface modification of pure niobium by plasma nitriding

Plasma nitriding of pure niobium was investigated using a dc square waveform pulsed power supply of 5.0kW, aiming to change the material surface characteristics due to heating and physical–chemical reactions caused by the ions and fast neutral bombardment during the treatment. Nitriding was performed for temperatures of 500, 750, 915 and 1080°C, at 90% N2+10% H2 gas mixture, pressure of 1200MPa (9Torr), at 300sccm gas flow rate and nitriding time of 7.2ks. Characterization of the samples was carried out by means of SEM, XRD, nanoindentation technique, scratch testing and roughness analysis. Strong increase of the surface hardness was verified. Nanoindentation results indicate values on the order of 2.5GPa for pure niobium in the start condition (as non-nitrided) and up to 21GPa in the as-nitrided condition. The XRD patterns show the presence of ε-NbN and β-Nb2N hexagonal phases in addition to the original Nb peaks. Significant changes on surface morphology and roughness of the treated samples were observed for the studied conditions and are discussed considering the sputtering and plasma species bombardment effect.

In situ Diamond Anvil Cell–Raman Spectroscopy and Nanoindentation Study of the Pressure‐Induced Phase Transformation in Pure and Zinc‐Doped β‐Eucryptite

β‐eucryptite (LiAlSiO4), a member of the family of lithium aluminum silicates, is known to undergo a reversible pressure‐induced phase transformation at ~0.8 GPa to ε‐eucryptite. This study correlates the results between two techniques, in situ diamond anvil cell–Raman spectroscopy and nanoindentation experiments, to explore how doping (substituting Zn for Li) influences this pressure‐induced phase transformation. Diamond anvil cell tests carried up to 3 GPa hydrostatic stress under Raman spectroscopy were compared with nanoindentation results, which provide a more localized, multiaxial stress state. The results indicate that the magnitude of hysteresis observed (difference between the pressures required for the forward and reverse transformation) is lower for Zn‐doped β‐eucryptite; however, the onset of the phase transformation is unchanged by doping with Zn. Furthermore, calculations of activation volume from nanoindentation experiments yield similar values (~0.1 nm3) for pure and Zn‐doped β‐eucryptite, suggesting that the nucleation event that establishes the onset of the phase transformation is the same for both materials.

Enhanced Hydrothermal Resistance of Y‐TZP Ceramics Through Colloidal Processing

Two commercial zirconia powders with 3 mol% of yttria (TZ3YE and TZ3YS, labeled as ZE and ZS, respectively) supplied by Tosoh (Japan) were used for this study. Maximum colloidal stability for ZE was achieved by dispersing the powders in a mixture of water/ethanol of 90:10 (wt/wt) using a sonication probe. The rheological behavior of the suspensions was optimized in terms of solids content ranging from 20 to 33 vol% and sonication time (0–6 min), the best results being obtained after 2 min. ZS samples were prepared to a solids loading of 30 vol% in water dispersing with 2 min‐sonication. Samples obtained by slip casting in plaster molds were used for dynamic sintering studies, and fully dense and nanostructured specimens were obtained at temperatures of 1300°C–1350°C (ZE samples) and 1400°C per 2 h (ZS samples). The Hardness (H) and Young's Modulus (E) properties of the specimens were studied by nanoindentation technique giving 17 and 250 GPa mean values for H and E, respectively. The specimens were then forced to a low‐temperature degradation (LTD) treatment at 130°C for 240 h in steps of 60 h. Raman spectroscopy and nanoindentation results of hydrothermally treated samples showed the absence of transformation from tetragonal to monoclinic phase until 180 h whereas the mechanical properties maintained constant even at the sample surface. After 240 h of LTD, the monoclinic phase was detected on all specimens by Raman peaks centered at 180, 191, and 383 cm−1. The nanoindentation study revealed an important loss of mechanical features reaching 10 and 175 GPa for H and E, respectively. In the case of the ZS specimens, no monoclinic phase is detected after 240 h of LTD treatment and no decay of E or H is detected. The free defect microstructure reached for the ZS specimen revealed a higher hydrothermal resistance so that it is concluded that the excellent behavior against thermal degradation is possible due to the large uniformity obtained by colloidal processing rather than the particle size of the starting powders.

Study of irradiation damage in borosilicate glass induced by He ions and electrons

Radiation effects on borosilicate glass induced by 0.5MeV He ions and 1.2MeV electrons have been investigated by nano-indentation and Raman measurements. The nano-indentation results indicated that the average hardness of the He-irradiated glasses were reduced by 14% with the nuclear energy deposition, and kept constant after the nuclear energy deposition exceeding 5×1020keV/cm3. By the Raman measurements, the polymerization of the silicate network was found to be enhanced by the electronic energy deposition in the electron-irradiated glasses. It is concluded that the nuclear energy deposition is the major factor for the evolution in the plastic response of the borosilicate glass, while the electronic energy deposition influences the change of silicate network and migration of alkaline, which causes sight change of the mechanical properties.

Effects of Indenter Tilt on Nanoindentation Results of Fused Silica: an Investigation by Finite Element Analysis

In reality, it is a common phenomenon to perform nanoindentation test while the indenter is not perpendicular to the sample, which would cause the properties such as hardness and elastic modulus of sample to be somehow different from the true values. In this paper, the effects of indenter tilt on the results of nanoindentation were studied by finite element analysis (FEA) simulation. The results were compared with indenter perpendicularly penetrating into a flat surface. Conclusions show that when the tilt indenter penetrates into specimen, the projected contact area varies widely. The tilt indentation could significantly influence the tendency of the force-displacement curves, and could also affect the hardness and elastic modulus of the specimen that obtained from the results. Finally, a simple method is given to correct the values of projected area, hardness and elastic modulus once tilt indentation happens. [doi:10.2320/matertrans.M2012400]

Plastic behaviour of microstructural constituents of cortical bone tissue: a nanoindentation study

A mechanical behaviour of bone tissues is defined by mechanical properties of its microstructural constituents. Also, those properties are important as an input for finite-element models of cortical bone to simulate its deformation and fracture behaviours at the microstructural level. The aim of this study was to investigate a post-yield behaviour of osteonal cortical bone’s microstructural constituents at different loading rates, maximum load levels and dwell times; nanoindentation with a spherical-diamond-tip indenter was employed to determine it. The nanoindentation results revealed significant difference in stiffness values of cortical bone’s microstructural features –interstitial matrix and osteons. Similarly, interstitial matrix exhibited a stiffer post-yield behaviour compared to that of osteons that reflects the relationship between the post-yield behaviour and collagen maturity. In addition, both osteons and interstitial matrix demonstrated a time-dependent behaviour. However, in order to assess elastic-plastic behaviour accurately, an effect of viscosity on nanoindentation results was reduced by using a time-delay method.

Functional polyaniline nanofibre mats for human adipose-derived stem cell proliferation and adhesion

Conductive polymer poly(aniline-co-m-aminobenzoic acid) (P(ANI-co-m-ABA)) and polyaniline (PANI) were blended with a biodegradable, biocompatible polymer, poly(l-lactic acid) and were electrospun into nanofibres to investigate their potential application as a scaffold for human adipose-derived stem cells (hASCs). These polymers, in both conductive and non-conductive form, were electrospun with average fibre diameters of less than 400 nm. Novel nanoindentation results obtained on the individual nanofibres revealed that the elastic moduli of the nanofibres are much higher at the surface (4–10 GPa, hmax <75 nm) than in the inner fibre core (2–4 GPa, hmax >75 nm). The composite nanofibres showed great promise as a scaffold for hASCs as they supported the cell adhesion and proliferation. After 1 week of cell culture hASCs were well spread on the substrates with abundant focal adhesions. The electrospun mats provide the cells with comparably stiff, sub-micron sized fibres as anchoring points on a substrate of high porosity. The conductive nature of these composite nanofibres offers exciting opportunities for electrical stimulation of the cells.

Microstructure and mechanical properties of the modified layer obtained by low temperature plasma nitriding of nanocrystallized 18Ni maraging steel

In the present study, low temperature plasma nitriding of nanocrystallized 18Ni maraging steel has been carried out at 360°C from 1 to 24h in a mixed gas of 25%N2+75%H2. The surface phase constitutions and microstructures of the nitrided layer have been investigated by X-ray diffraction analysis, transmission electron microscopy and optical microscopy. Nanoindentation and microhardness tests have been performed to determine the surface hardness and the hardness profile in the nitrided layer. The plasticity of the nitrided surface has been analyzed based on the nanoindentation results. The results show that at the initial stage of nitriding, the surface phase consists of a solid solution of nitrogen in α-Fe, and nanoscale nitrides and aging phase are formed with increasing of treatment time. The surfaces nitrided for 8 and 16h possess the highest hardness. The plasticity factor calculations suggest that the nitrided surfaces have a good wear resistance and possess excellent plasticity.

Nanoindentation and Wear Characteristics of Al 5083/SiCp Nanocomposites Synthesized by High Energy Ball Milling and Spark Plasma Sintering

Al 5083/10 wt% SiC p nano composites have been synthesized by means of high energy ball milling followed by spark plasma sintering (SPS). Nano composites produced via this method exhibited near-theoretical density while retaining the nano-grained features. X-ray diffraction (XRD) analysis indicated that the crystalline size of the ball milled Al 5083 matrix was observed to be ∼25 nm and it was coarsened up to ∼30 nm after SPS. Nano indentation results of nano composites demonstrated a high hardness of ∼280 HV with an elastic modulus of 126 GPa. Wear and friction characteristics with addition of SiC p reinforcement exhibited significant improvement in terms of coefficient of friction and specific wear rate to that of nano structured Al 5083 alloy. The reduction in specific wear rate in the nanocomposite was mainly due to the change of wear mechanism from adhesive to abrasive wear with the addition of SiC P which resulted in high hardness associated with nano-grained microstructure.

Photocatalytic WO3 and TiO2 Films on Brass

This paper reports on the structure, mechanical, and photocatalytic properties of titanium dioxide (TiO2) and tungsten oxide (WO3) films on a brass substrate. TiO2 and WO3 films have been successfully deposited on brass by a simple sol‐gel dip‐coating method and it has been shown that, while both films possess photocatalytic properties, WO3 films were superior to TiO2. Higher surface area and rod‐like morphology of WO3 films might have contributed to their higher photocatalytic activity. Nanoindentation results have shown that both films attach well to the substrate and possess good mechanical properties.

Nanomechanical properties of GaSe thin films deposited on Si(1 1 1) substrates by pulsed laser deposition

The correlations between the crystalline structure and mechanical properties of GaSe thin films were investigated by means of X-ray diffraction (XRD) and nanoindentation techniques. The GaSe thin films were deposited on Si(111) substrates deposited at various deposition temperatures using pulsed laser deposition (PLD). The XRD results indicate that all the GaSe thin films are pure hexagonal phase with highly (000l)-oriented characteristics. Nanoindentation results revealed apparent discontinuities (so-called multiple “pop-in” events) in the load-displacement curve, while no discontinuity was observed in the unloading segment of the load-displacement curve. The hardness and Young’s modulus of GaSe thin films determined by the continuous stiffness measurements (CSM) method indicated that both mechanical parameters increased with the increasing deposition temperature with the hardness and the Young’s modulus being increased from 1.2±0.1 to 1.8±0.1GPa and from 39.6±1.2 to 68.9±2.7GPa, respectively, as the deposition temperature was raised from 400 to 475°C. These results suggest that the increased grain size might have played a prominent role in determining the mechanical properties of the PLD-derived GaSe thin films.

Nanotechnology and construction: use of nanoindentation measurements to predict macroscale elastic properties of high strength cementitious composites

This paper aims to present the experimental results involving the use of nanoindentation measurements and prediction of macroscale elastic properties of high performance cementitious composites (HPCC). The elastic properties of HPCC mixture were evaluated at different length scales by nanoindentation (microscale), and elastic moduli and compressive strength tests (macroscale). The nanoindentation results, obtained by grid indentation with subsequent phase deconvolution, were complemented by an independent porosimetry test and inserted into a two-step analytical homogenization scheme to predict the overall macroscale properties. The final results show that the presented method allows a reliable advanced prediction of HPCC elastic properties indicating, thus, that inserting nanotechnology in the concrete industry can be promising, since it would allow the production of a more predictable composite in an easier and less expensive way.

Strain rate effect on the fatigue failure of thin PVD coatings: An investigation by a novel impact tester with adjustable repetitive force

Physical vapor deposition (PVD) coated surfaces are often subjected to repetitive impact loads. In such cases, the strain rate’s effect on the coating fatigue failure is pivotal. This effect was investigated via a novel impact tester which facilitates the modulation of the applied impact force versus the time through an adjustable piezoelectric actuator. Using the developed test arrangement, impact loads of various patterns, frequencies and durations were generated and the coated specimens’ surface response and film fatigue fracture were captured. Based on these results, it was possible to correspond impact forces of various data to equivalent quasi static ones which induce approximately the same coating and substrate deformation. At the latter loads, the coated specimen deformation was determined by Finite Element Method (FEM) calculations taking into account elastic–plastic film and substrate properties attained by an analytical evaluation of nanoindentation results. Moreover, strain, strain rate combinations insuring film fatigue endurance after one million impacts were estimated.

Measuring the Surface and Bulk Modulus of Polished Polymers with AFM and Nanoindentation

A new method to determine the elastic modulus of a material using the atomic force microscope (AFM) was proposed by Tang et al. [Nanotechnology 19, 495713 (2008)] and is used in this study. This method models the cantilever and the sample as two springs in a series. The properties of both the spring and cantilever are determined on two reference samples with known mechanical properties and these properties are then used to find the elastic modulus of an unknown sample. The indentation depth achieved with AFM is in the nanometer range (30–130 nm in this study); and hence when this technique is performed on polymers, whose surface structure is different from their bulk structure, AFM gives a measure of the surface elastic modulus. In the present study, after employing AFM to measure the surface modulus of five polymers, traditional depth-sensing nanoindentation, with penetration depths of about 1 μm, was used to determine the elastic modulus in the bulk. The mean values for elastic modulus from the AFM were within 5–50% of the nanoindentation results, suggesting the existence of a surface modulus for polished polymers.

Crystal size and direction dependence of the elastic properties of Cu3Sn through molecular dynamics simulation and nanoindentation testing

The study aims at exploring the elastic properties of orthorhombic Cu3Sn crystals through a proposed molecular dynamics (MD) simulation model based on the modified embedded atom method (MEAM) and nanoindentation testing. The focuses of the study are placed on their dependence on the crystal size and direction. The electronic nature of single crystal Cu3Sn is also examined by using first-principles calculations based on density function theory (DFT). According to continuum mechanics, the elastic stiffness coefficients of the single crystal Cu3Sn are derived from the calculated energy, and used in the generalized Hook’s law in compliance form to compute the associated elastic constants. The simulated elastic properties are compared with the results of the published first-principles calculations. For comparison with the present nanoindentation finding and the other published experimental data, the effective elastic properties of the polycrystalline Cu3Sn together with their size dependence are also derived using the Voigt–Reuss bounds and Voigt–Reuss–Hill average based on the calculated single crystal data.The simulation results show that the orthorhombic Cu3Sn crystals exhibit a high elastic anisotropy, which has been also confirmed by the electronic structure analysis, and also a strong size and direction dependence of elasticity. In addition, the calculated effective elastic properties of the polycrystalline Cu3Sn agree well with the present nanoindentation results and the published theoretical/experimental data.

Multiscale simulations of nanoindentation and nanoscratch of single crystal copper

In this paper, a three-dimensional multiscale method coupling molecular dynamics (MD) and finite element (FE) analysis has been employed to study nanoindentation and nanoscratch processes of copper thin film. During the nanoindentation process, no discontinuities can be observed in the displacement gradient, which demonstrates a seamless coupling between MD and FE regions. The multiscale model of nanoindentation is further validated by the fact that the load–depth curves obtained from both multiscale and full MD simulations match each other reasonably well. The nanoindentation results using multiscale model are also compared with those using part MD model to elucidate the advantages of multiscale method. The multiscale simulation results of nanoindentation show that the indentation velocity has a great effect on the load–depth curve and hardness of copper. The continuity of displacement field during the nanoscratch also demonstrates a seamless information exchange between MD and FE regions. The deformation of substrate and forces in the nanoscratch process are also investigated using the multiscale method. The multiscale method can greatly expand the system size to be explored without significant increase in computational cost.

OS1906 ナノ構造体を形成した層間絶縁膜の機械的特性の評価

Semiconductor devices are getting smaller and smaller, which lead to some problems such as cross-talk and signal delay. Therefore, the low-dielectric insulating layer is necessary for semiconductor devices. To overcome this problem, we propose a nano-structured insulating layer. Nano-sized structure is orderly aligned, which are made by dynamic oblique deposition (DOD). The size and structure of structure can be controlled in DOD method and, thus, the amounts of air space in insulating layer are able to be controlled. The objective of this study is to present the way to measure Elastic modulus about multilayer thin films, and to measure elastic modulus of nano-structured insulating layer. Multilayer structure is modeled as serial springs, so we obtain the elastic modulus of nano-structured insulating layer from nano-indentation results. The results show that elastic modulus of nano-structured insulating layer is mainly influenced by the volume density of nano-structures.

Processing and nanomechanical properties of chitosan/polyethylene oxide blend films

Chitosan based films have found an increasing implementation in variety of topics among which as drug delivery carriers, in packaging industry and as water puritication filters. Therefore, in order to achieve mechanical integrity of such films while preserving processability and biocompatibility, chitosan based films are fabricated in forms of blends with polyethylene oxide (PEO). Nanoindentation study is undertaken in order to investigate nanomechanical properties and surface morphology of chitosan films in blends with various content of PEO. Results of differential scanning calorimetry, water uptake and nanoindentation revealed that films with 80/20 blend ratio of chitosan/PEO showed the optimal values of reduced modulus and hardness. It appears that the incorporation of synthetic PEO in chitosan films could lower the manufacturing cost while preserving the mechanical integrity of the films.

Preparation, characterization and mechanical properties of rare-earth-based nanocomposites

This study reports research related to different preparation methods and characterization of polymer nanocomposites for optical applications. The Eu-ion doped Gd2O3 nanophosphor powder with different nanoparticle content was embedded in the matrix of PMMA. Preparation was carried out by mixing molding (bulk), electrospinning (nanofibers) and solution casting (thin films) with neat particles and particles coated with AMEO silane. Among the pros and cons for proposed methods, the mixing molding enables to avoid solvent use while the best deagglomeration and nanoparticle distribution is gained using the electrospinning method. The results of dynamic mechanical analysis (DMA) and nanoindentation revealed that the storage modulus of the composites was higher than that of pure PMMA and increased with nanophosphor content. Surface modification of particles improved the mechanical properties of nanocomposites.