Continuous Stiffness Measurement Research Articles

The continuous stiffness measurement technique in nanoindentation intrinsically modifies the strength of the sample

The continuous stiffness measurement (CSM) method is a well-established technique for obtaining elastic modulus and hardness data continuously during a nanoindentation process. The applicability of this technique is based on the assumption that the material properties of the specimen being tested are not affected by the imposed oscillatory excitation of the indenter. In this study, nanoindentation experiments on aluminium with a Berkovich tip show that nanometric oscillations of the CSM can lead to significant softening even though the indents made are micron-sized. The amount of softening is similar to that observed from macroscopic indentation tests with simultaneous ultrasonic excitation of similar displacement/amplitude ratios. Electron microscopy analyses reveal subgrain formation under the CSM nanoindents, which is also a feature of ultrasonically deformed bulk aluminium. The Oliver–Pharr and CSM method of hardness measurement are found to be erroneous with the CSM mode switched on.

Dense and Cellular Zirconia Produced by Gel Casting with Agar: Preparation and High Temperature Characterization

A modified gel‐casting process was developed to produce both dense and highly porous (40% volume) yttria tetragonal zirconia polycrystal (Y‐TZP) using agar, a natural polysaccharide, as gelling agent. A fugitive phase, made of commercial polyethylene spheres, was added to the ceramic suspension before gelling to produce cellular ceramic structures. The characterization of the microstructural features of both dense and cellular ceramics was carried out by FEG SEM analysis of cross‐sections produced by focused ion beam. The mechanical properties of the components were characterized at room temperature by nanoindentation tests in continuous stiffness measurement mode, by investigating the direct effect of the presence of residual microporosity. The presence of a diffuse residual microporosity from incomplete gel deaeration resulted in a decay of the bending strength and of the elastic modulus. The mechanical behavior of both dense and cellular zirconia (in terms of elastic modulus, flexural strength, and deformation at rupture) was investigated by performing four‐point bending tests at the temperature of 1500°C.

Nanoindentation Assessment of the Interphase in Carbon Nanotube-Based Hierarchical Composites

Optimizing the interphase properties in polymer–fiber laminates represents a major issue in the development of materials for high structural applications. Carbon nanotube-based hierarchical composites offer a challenging route to produce polymer–fiber laminates with enhanced interlaminar properties. The influence of nanotube reinforcement on the interphase properties between the polymer matrix and the microfiber is of major concern and drives the present study. Nanoindentation is used to explore the local mechanical properties of single-walled carbon nanotube (SWCNT)-based multiscale (or hierarchical) composites comprising glass fiber mats alternated with SWCNT-reinforced poly(ether ether ketone). The continuous stiffness measurement (CSM) technique is used to determine elastic modulus and hardness at the fiber, at the matrix, and across the interface, as a function of indentation depth from small penetrations of around 50 nm. It is shown that the polymer–fiber interface can be readily detected using CSM....

Nanomechanical properties of pure and doped Ta2O5 and the effect of microwave irradiation

The nanomechanical properties of pure and doped Ta2O5 films (100 nm) on Si, and the effect of short time (10 s) microwave irradiation are studied by nanoindentation testing. The local mechanical parameters as determined by the force measuring ability of atomic force microscopy are compared with the data from both the Oliver–Pharr nanoindentation technique and the continuous stiffness measurements. The impact of the dopant type (Hf and Al) on the surface morphology, elastic modulus and hardness of the films is determined. The results reveal an increase in elastic modulus and hardness after the doping. The irradiation produces a little lower values of mechanical parameters. The results are discussed in juxtaposition with the established previously strong effect of irradiation on the electrical properties of Ta2O5-based stacks. From device perspective point of view Hf-doped Ta2O5 is noteworthy for micro-electro-mechanical system applications.

Influence of Mg-containing precursor flow rate on the structural, electrical and mechanical properties of Mg-doped GaN thin films

The effects of Mg-containing precursor flow rate on the characteristics of the Mg-doped GaN (GaN:Mg) were systematically studied in this study. The GaN:Mg films were deposited on sapphire substrates by metal-organic chemical-vapor deposition (MOCVD) with various flow rates of 25, 50, 75 and 100 sccm of bis-(cyclopentadienyl)-magnesium (Cp2Mg) precursor. The structural, electrical and nanomechanical properties of GaN:Mg thin films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), Hall measurement and nanoindentation techniques, respectively. Results indicated that GaN:Mg films obtained with 25 sccm Cp2Mg possess the highest hole concentration of 3.1 × 1017 cm−3. Moreover, the hardness and Young's modulus of GaN:Mg films measured by a Berkovich nanoindenter operated with the continuous contact stiffness measurements (CSM) option showed positive dependence with increasing flow rate of Cp2Mg precursor, presumably due to the solution hardening effect of Mg-doping.

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.

Nanoindentation of GaSe thin films

The structural and nanomechanical 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 by pulsed laser deposition. XRD patterns reveal only the pure (000 l)-oriented reflections originating from the hexagonal GaSe phase and no trace of any impurity or additional phases. Nanoindentation results exhibit discontinuities (so-called multiple ‘pop-in’ events) in the loading segments of the load–displacement curves, and the continuous stiffness measurements indicate that the hardness and Young’s modulus of the hexagonal GaSe films are 1.8 ± 0.2 and 65.8 ± 5.6 GPa, respectively.

Rapid thermal annealing effects on the structural and nanomechanical properties of Ga-doped ZnO thin films

In this study, the structural and nanomechanical properties of Ga-doped ZnO (GZO) thin films on glass substrates followed by rapid thermal annealing (RTA) process were investigated by X-ray diffraction (XRD), atomic force microscopy (AFM) and nanoindentation techniques. The XRD results indicated that the annealed GZO thin films are textured, having a preferential crystallographic orientation along the hexagonal wurtzite (002) axis. Both the grain size and surface roughness of the annealed GZO thin films exhibit an increasing trend after RTA treatment. The hardness and Young's modulus of the annealed GZO thin films were measured by a Berkovich nanoindenter operated with the continuous contact stiffness measurements (CSM) option. Furthermore, the hardness and Young's modulus were found to increase with increasing grain size when the RTA time was prolonged from 0.5 to 3min. The deformation behavior is referred to the inverse Hall–Petch effect commonly observed in systems deformed primarily via grain boundary sliding. The suppression of dislocation movement-associated deformation mechanism might be arisen from strong pinning effects introduced by Ga-doping.

Effects of intra-crystalline microcracks on the mechanical behavior of a marble under indentation

Indentation tests have been carried out on a marble in order to define the role of the intra-grain microcracks on its mechanical behavior. The investigated marble shows a strong variability in grain-texture (granoblastic to xenoblastic) also on the scale of centimeter and contains different types of microdiscontinuities (cleavage cracks, grain boundaries cracks), despite the almost monomineralic composition of calcite crystals. The mechanical properties of the calcite grains have been determined by applying static non-instrumented Vickers and Knoop indentations and Berkovich nanoindentation in Continuous Stiffness Measurements (CSM) mode. The study has clearly revealed the influence of microcracks on the mechanical strength and deformability characteristics of the investigated rock, even on the smallest scales.

Morphology and dispersion state of Ba2TiSi2O8 nanocrystals in transparent glass-ceramics and their nanoindentation behavior

The morphology and dispersion state of Ba2TiSi2O8 (BTS) nanocrystals in transparent glass-ceramics (composition: 40BaO–20TiO2–40SiO2) were examined from high resolution transmission electron microscope observations, and their nano-scale deformation behavior was examined using Berkovich nanoindentation technique (standard-type and continuous stiffness measurement (CSM)-type). In the early stage of crystallization, BTS crystalline layers with a thickness of ~120 nm were formed at the surface and ellipsoid-shaped crystallites with a diameter of 100–200nm were dispersed in the glass matrix. In the late stage, BTS crystals with a diameter of 200–400nm were formed densely, but a glassy phase was present between BTS crystals. The Young's modulus evaluated from CSM-type nanoindentation measurements for a deformation scale of about 100nm shows the values of 98GPa for the glass and 110GPa for the glass-ceramics with nanocrystals. It was suggested that CSM-type measurements are very sensitive in the nano-scaled homogeneity in the heat-treated samples.

Porous chitosan scaffold cross-linked by chemical and natural procedure applied to investigate cell regeneration

Porous chitosan scaffold is used for tissue engineering and drug delivery, but is limited as a scaffold material due to its mechanical weakness, which restrains cell adhesion on the surface. In this study, a chemical reagent (citrate) and a natural reagent (genipin) are used as cross-linkers for the formation of chitosan-based films. Nanoindentation technique with a continuous stiffness measurement system is particularly applied on the porous scaffold surface to examine the characteristic modulus and nanohardness of a porous scaffold surface. The characteristic modulus of a genipin-cross-linked chitosan surface is ≈2.325GPa, which is significantly higher than that of an uncross-linked one (≈1.292GPa). The cell-scaffold surface interaction is assessed. The cell morphology and results of an MTS assay of 3T3-fibroblast cells of a genipin-cross-linked chitosan surface indicate that the enhancement of mechanical properties induced cell adhesion and proliferation on the modified porous scaffold surface. The pore size and mechanical properties of porous chitosan film can be tuned for specific applications such as tissue regeneration.

Indentation size effect in FCC metals: An examination of experimental techniques and the bilinear behavior

Abstract

A HRXRD and nano-indentation study on Ne-implanted 6H–SiC

Specimens of 6H–SiC single crystal were irradiated at room temperature with 2.3MeV neon ions to three successively increasing fluences of 2×1014, 1.1×1015 and 3.8×1015ions/cm2 and then annealed at room temperature, 500, 700 and 1000°C, respectively. The strain in the specimens was investigated with a high resolution XRD spectrometer with an ω-2θ scanning. And the mechanical properties were investigated with the nano-indentation in the continuous stiffness measurement (CSM) mode with a diamond Berkovich indenter. The XRD curves of specimens after irradiation show the diffraction peaks arising at lower angles aside of the main Bragg peak ΘBragg, indicating that a positive strain is produced in the implanted layer. In the as-implanted specimens, the strain increases with the increase of the ion fluence or energy deposition. Recovery of the strain occurs on subsequent thermal annealing treatment and two stages of defects evolution process are displayed. An interpretation of defects migration, annihilation and evolution is given to explain the strain variations of the specimens after annealing. The nano-indentation measurements show that the hardness in as-implanted specimens first increases with the increase of the ion fluence, and a degradation of hardness occurs when the ion fluence exceeds a threshold. On the subsequent annealing, the hardness variations are regarded to be a combined effect of the covalent bonding and the pinning effect of defect clusters.

Indentation‐Induced Mechanical Deformation Behaviors of AlN Thin Films Deposited on c‐Plane Sapphire

The mechanical properties and deformation behaviors of AlN thin films deposited on c‐plane sapphire substrates by helicon sputtering method were determined using the Berkovich nanoindentation and cross‐sectional transmission electron microscopy (XTEM). The load‐displacement curves show the “pop‐ins” phenomena during nanoindentation loading, indicative of the formation of slip bands caused by the propagation of dislocations. No evidence of nanoindentation‐induced phase transformation or cracking patterns was observed up to the maximum load of 80 mN, from either XTEM or atomic force microscopy (AFM) of the mechanically deformed regions. Instead, XTEM revealed that the primary deformation mechanism in AlN thin films is via propagation of dislocations on both basal and pyramidal planes. Furthermore, the hardness and Young’s modulus of AlN thin films estimated using the continuous contact stiffness measurements (CSMs) mode provided with the nanoindenter are 16.2 GPa and 243.5 GPa, respectively.

Viscoelastic properties of wood materials characterized by nanoindentation experiments

The viscoelastic properties of the cell wall of the tropic hardwood Carapa procera are investigated by means of nanoindentation tests. Three types of nanoindentation tests are undertaken: creep, continuous stiffness measurement (CSM) and nanoscale dynamic mechanical analysis (Nano-DMA), corresponding to the increased loading rate and so the response of wood cell wall to the loading in a relatively large time scale. It is found that the creep rate is dependent on the applied stress and the relation can be described by the rule of power law. Regarding the dynamic properties (i.e., storage modulus and damping coefficient) in the frequency range of 10–240 Hz, it is shown that the storage modulus increases monotonically, while the damping coefficient decreases. By using the traditional dynamic mechanical thermal analysis as a reference method, the phase transition behavior of wood cell wall can be successfully characterized by the Nano-DMA in a large frequency scale. A dependence of the storage modulus and damping coefficient on the penetration depth is quantified by the CSM tests.

Synthesis, microstructural, optical and mechanical properties of yttria stabilized zirconia thin films

Thin films of yttria-stabilized zirconia (YSZ) exhibit exceptional properties, such as high thermal, chemical and mechanical stability. Here, we report the synthesis of YSZ thin films by aerosol assisted chemical vapour deposition onto borosilicate glass and fused silica substrates. Optimum deposition temperature was 673±5K. In addition, different Y content was tried to analyse its influence in the microstructure and properties of the films. The films were uniform, transparent and non-light scattering. Surface morphology and cross sectional microstructure were studied by field emission scanning electron microscopy. The microstructure of the films was characterized by grazing incidence X-ray diffraction. Crystallite size and lattice parameter were obtained. Optical properties were analysed from reflectance and transmittance spectra; from these measurements, optical constants and band gap were obtained. Quantum confinement effect, due to the small grain size of the films, was evident in the high band gap energy obtained. Nanoindentation tests were realized at room temperature employing the continuous stiffness measurement method, to determine the hardness and elastic modulus as a function of Y content.

Comparison of methods for the mechanical characterization of polymers for MEMS applications

This paper gives an overview of a series of experiments conducted in order to characterize the mechanical behavior of two photodefinable epoxies. In particular, it focuses on the stiffness of the materials. The (complex) modulus is measured using five different methods: conventional nanoindentation, continuous stiffness measurement nanoindentation, nanoindentation on MEM structures, dynamic tensile tests and static tensile tests. The measured moduli range from 0.9 to 7.4 GPa for SU-8 and from 1 to 4.1 GPa for Epoclad, depending on the type of experiment and the loading speeds used in the experiments. Results reveal that conventional nanoindentation is not well optimized for polymer characterization and that there is a need for stiffness measurements using more fundamental approaches like a (dynamic) tensile test.

Nanomechanical properties of magnesium-based hybrid composites with graphite nanofiber and alumina short fiber

In this study, an attempt was made to evaluate the nanomechanical properties of magnesium-based hybrid composites with graphite nanofibers (GNFs) and alumina short fibers (Al2O3sf) by nanoindentation. The nanoindentation was performed using continuous stiffness measurement (CSM) method with an indentation depth of 2000 nm. To find out the modulus and hardness of composites of local regions, indentation tests were carried out in different locations of the sample, such as GNFs/Al2O3sf region, Al2O3sf region, GNFs cluster, and Mg matrix. The modulus and hardness values closer to the GNFs/Al2O3sf region are higher than those of the corresponding to the other regions primarily because of a higher constraint to the localized matrix deformation during indentation. Furthermore, the presence of GNFs can act as a barrier for movement of dislocations enhancing the indentation properties. The presence of MgO/Mg17Al12 also can contribute to improve the nanoindentation properties of the present composite system.

Determination of the True Young's Modulus of Pb(Zr0.52Ti0.48)O3 Films by Nanoindentation: Effects of Film Orientation and Substrate

PZT films were deposited by the sol‐gel method on platinized silicon substrates with silicon nitride and silicon oxide structural layer materials. The crystalline orientations of the PZT films were controlled by both a chelating agent and pyrolysis temperature. A nanoindentation CSM (continuous stiffness measurement) technique was utilized to characterize the Young's moduli of these PZT films. It was found that the measured moduli of PZT films on the two types of substrates showed similar orientation dependence (E001 > E111>E(110,111)) but distinct values, which indicated a clear substrate effect. By using a new model of film indentation, we were able to decouple the effects of film orientation and structural layer type on the Young's modulus.

Mechanical Properties and Defect Evolution of Kr-Implanted 6H-SiC

Specimens of silicon carbide (6H-SiC) were irradiated with 5 MeV Kr ions (84Kr19+) for three fluences of 5×1013, 2 ×1014 and 1× 1015 ions/cm2, and subsequently annealed at room temperature, 500°C, 700°C and 1000°C, respectively. The strain of the specimens was investigated with high resolution XRD and different defect evolution processes are revealed. An interpretation of the defect evolution and migration is given to explain the strain variation. The mechanical properties of the specimens were studied by using a nano-indentation technique in continuous stiffness measurement (GSM) mode with a diamond Berkovich indenter. For specimens irradiated with fluences of 5×1013 or 2×1014 ions/cm2, hardness values exceed that of un-implanted SiC. However, hardness sharply degrades for specimens irradiated with the highest fluence of 1×1015 ions/cm2. The specimens with fluences of 5×1013 and 2×1014 ions/cm2 and subsequently annealed at 700°C and 500°C, respectively, show the maximum hardness value.