Continuous Stiffness Measurement Research Articles

The Microstructures and Characteristics of NiO Films: Effects of Substrate Temperature.

The influence of the substrate temperature on the structural, surface morphological, optical and nanomechanical properties of NiO films deposited on glass substrates using radio-frequency magnetron sputtering was examined by X-ray diffraction (XRD), atomic force microscopy (AFM), UV-Visible spectroscopy and nanoindentation, respectively. The results indicate that the substrate temperature exhibits significant influences on both the grain texturing orientation and surface morphology of the films. Namely, the dominant crystallographic orientation of the films switches from (111) to (200) accompanied by progressively roughening of the surface when the substrate temperature is increased from 300 °C to 500 °C. The average transmittance of the NiO films was also found to vary in the range of 60-85% in the visible wavelength region, depending on the substrate temperature and wavelength. In addition, the optical band gap calculated from the Tauc plot showed an increasing trend from 3.18 eV to 3.56 eV with increasing substrate temperature. Both the hardness and Young's modulus of NiO films were obtained by means of the nanoindentation continuous contact stiffness measurements mode. Moreover, the contact angle between the water droplet and film surface also indicated an intimate correlation between the surface energy, hence the wettability, of the film and substrate temperature.

Finite Element Analysis of Nanoindentation Responses in Bi2Se3 Thin Films

In this study, the nanoindentation responses of Bi2Se3 thin film were quantitatively analyzed and simulated by using the finite element method (FEM). The hardness and Young’s modulus of Bi2Se3 thin films were experimentally determined using the continuous contact stiffness measurements option built into a Berkovich nanoindenter. Concurrently, FEM was conducted to establish a model describing the contact mechanics at the film/substrate interface, which was then used to reproduce the nanoindentation load-depth and hardness-depth curves. As such, the appropriate material parameters were obtained by correlating the FEM results with the corresponding experimental load-displacement curves. Moreover, the detailed nanoindentation-induced stress distribution in the vicinity around the interface of Bi2Se3 thin film and c-plane sapphires was mapped by FEM simulation for three different indenters, namely, the Berkovich, spherical and flat punch indenters. The results indicated that the nanoindentation-induced stress distribution at the film/substrate interface is indeed strongly dependent on the indenter’s geometric shape.

Determination of peak ordering in the CrCoNi medium-entropy alloy via nanoindentation

Local chemical ordering (LCO) in the CrCoNi medium-entropy alloy was investigated by transmission electron microscopy (TEM) after different annealing treatments and their corresponding mechanical properties by bulk tensile tests and nanoindentation. A cold-rolled alloy was annealed at 1000°C for 0.5 h followed by ice water quenching and then aged at a number of different temperatures (600°C, 700°C, 800°C, 900°C, and 1000°C) under vacuum for 240 h to generate different degrees of chemical ordering. A splat-quenched sample rapidly cooled from the liquid phase was also examined. While bulk mechanical properties did not vary among samples with equivalent grain sizes, nanoindentation tests revealed notable differences. As indicated by the load at first pop-in using a Berkovich tip or the indentation yield strength via continuous stiffness measurements using a 10 μm spherical tip, the nanoindentation tests revealed that the stress for onset of plasticity during indentation varied with heat treatment and peaked in the 900°C aged sample. Energy-filtered TEM characterization indicated the presence of ordering in all specimens, with a higher degree of LCO in the aged samples relative to the splat-quenched and 1000°C-quenched samples. The evolution of LCO during aging was determined to occur on the time scale similar to those of bulk diffusion. The difference in nanoindentation strength was attributed to the difference in dislocation nucleation barriers imposed by different degrees of LCO.

Nano-mechanical properties of Mo coating prepared on Invar alloy substrate by double glow plasma surface alloying

In this work, surface Mo alloying was realized on Invar alloy using double glow plasma surface alloying technology. The microstructure and phase constitution of Mo-modified coating were determined by using X-ray diffraction and scanning electron microscopy. The surface modification effect and loading strain rate (LSR) dependency of Mo coating were presented qualitatively and quantitatively via nanoindentation method based on continuous stiffness measurement technique. Results showed that the received Mo coating with a thickness of approximately 10 μm was compact and homogeneous. The phase constitution consisted of pure Mo phase. Double glow plasma surface molybdenizing improved the surface hardness and elastic modulus remarkably. Indentation response showed obvious LSR dependency. Under different LSRs, hardness and plasticity exponent increased with LSR, while elastic modulus and contact stiffness basically remained stable. Meanwhile, creep displacement and creep strain rate sensitivity exponent were positively correlated with LSR.

In situ damping identification of plant fiber composites using dynamic grid nanoindentation

Damping properties of plant fiber composites have been quite widely investigated based on macroscale techniques. Considering their heterogeneous and hierarchical microstructure, it is also necessary to study their damping behavior at the microscale to provide better insight into the dissipation origins and mechanisms. This article proposes a characterization of the dynamic mechanical properties of flax/GreenPoxy composites at microscale using dynamic grid nanoindentation technique. Two loading protocols are used: the classical Continuous Stiffness Measurement method (CSM) and a new method called Constant Amplitude Measurement method (CAM). Results show experimental protocols (CAM or CSM) do not have significant effect on storage modulus while they significantly affect the loss factor. The grid nanoindentation technique also provides an interesting map of the viscoelastic properties at the microscale in the cross-section of the composites and the damping contribution of the various components are highlighted.

Effects of Substrate Temperature on Nanomechanical Properties of Pulsed Laser Deposited Bi2Te3 Films

The correlations among microstructure, surface morphology, hardness, and elastic modulus of Bi2Te3 thin films deposited on c-plane sapphire substrates by pulsed laser deposition are investigated. X-ray diffraction (XRD) and transmission electron microscopy are used to characterize the microstructures of the Bi2Te3 thin films. The XRD analyses revealed that the Bi2Te3 thin films were highly (00l)-oriented and exhibited progressively improved crystallinity when the substrate temperature (TS) increased. The hardness and elastic modulus of the Bi2Te3 thin films determined by nanoindentation operated with the continuous contact stiffness measurement (CSM) mode are both substantially larger than those reported for bulk samples, albeit both decrease monotonically with increasing crystallite size and follow the Hall—Petch relation closely. Moreover, the Berkovich nanoindentation-induced crack exhibited trans-granular cracking behaviors for all films investigated. The fracture toughness was significantly higher for films deposited at the lower TS; meanwhile, the fracture energy was almost the same when the crystallite size was suppressed, which indicated a prominent role of grain boundary in governing the deformation characteristics of the present Bi2Te3 films.

In situ micromechanical analysis of a nano-crystalline W-Cu composite

W-Cu composites are commonly used as heat-sinks or high-performance switches in power electronics. To enhance their mechanical properties and mutually their usability, grain refinement of the initially coarse-grained microstructure was realized using high–pressure torsion. This leads to different microstructural conditions, exhibiting fine-, ultrafine-grained or nanocrystalline microstructures. Scanning as well as transmission electron microscopy was performed to analyze the respective grain size and microstructures. The hardness and Young’s modulus of the deformed specimens were quantified by nanoindentation testing. Furthermore, X–ray diffraction indicated a decreased grain size and changed lattice spacings upon increasing the deformation ratio. The deformed specimens were tested for their fracture behaviour by continuous stiffness measurements during in-situ microcantilever bending experiments. Here, mean J–integral values of 288 ± 38 J/m2 and 402 ± 89 J/m2 were determined for the 5 and 50 times turned specimens, respectively. The combination of different characterization methods applied on a W–Cu composite allows to identify both, beneficial and unfavourable microstructural components regarding the fracture properties.

On the anisotropic indentation modulus and anisotropic creep behavior of [formula omitted]-Sn characterized by nanoindentation methods

The influence of the orientation on the indentation modulus, the hardness and the creep properties of high purity β-Sn (wt.%: 99.999) have been examined. Nanoindentation methods were used in order to evaluate their potential usage for analyzing small volumina commonly found at solder joints. Crystal orientations close to <100>, <110> and <001> were identified using electron backscatter diffraction (EBSD). To determine the indentation modulus and hardness, continuous stiffness measurements (CSM) were carried out with a maximum load of 1 mN. The indentation moduli correspond in basic sequence to Young’s moduli calculated using compliance data of single crystalline β-Sn. The creep properties were investigated using a constant load of 10 mN over a duration of 10 min. An orientation dependence in the obtained values for the indentation modulus, the hardness and the creep properties could be detected by methods of nanoindentation and is discussed in this study.

Nanoindentation characterization of nanocomposites coating based on graphene and siloxane matrix deposited by dielectric barrier discharge plasma

Hexamethyldisiloxane (HMDSO)/Graphene nanosheets (GNs) nanocomposite coatings were deposited by a dielectric barrier discharge at atmospheric pressure. Commercially available GNs were incorporated into HMDSO precursor at different concentrations up to 2 wt%. The nanocomposite coatings were analyzed using scanning electron microscopy (SEM) and nanoindentation test. Based on SEM images, it was found that the GNs were well distributed and dispersed in the plasma polymerized hexamethyldisiloxane (ppHMDSO) matrix with no significant agglomeration. The results of nanoindentation tests performed with the continuous stiffness measurements mode showed an increase in the hardness and reduced Young's modulus with the increase of graphene nanosheets percentage. The maximum increase was two orders of magnitude for 2% GNs/ppHMDSO nanocomposite coatings compared to the homopolymer ppHMDSO. Furthermore, the creep compliance analysis showed that the nanocomposite coatings exhibited a viscoelastic behavior compared to the plasma polymer homopolymer.

Indentation characterization of glass/epoxy and carbon/epoxy composite samples aged in artificial salt water at elevated temperature

Micro-level composite properties are a key determinant of the long-term performance and life span of marine-based composite structures. In this paper, the effect of the aging process in salt water at room temperature and elevated temperature on the elastic modulus and hardness of composite specimens have been investigated through indentation testing. To do this, carbon/epoxy (CE) and glass/epoxy (GE) samples were immersed in artificial sea water with 3.5% salinity at room temperature and 60 °C for 90 days. Matrix only and fibre/matrix (fibre constraint) cells have been examined by two different approaches, namely standard indentation testing and continuous stiffness measurement (CSM) methods to measure elastic modulus and hardness in micro level. It was indicated that degradation at 60 °C had a higher effect on elastic modulus than the room temperature aging process. According to the experimental results from the standard method indentation in matrix cells, the average modulus in the aged GE in 60 °C was 3.47 ± 0.1 GPa (22.3% loss). The average modulus in the reference CE samples was 4.7 ± 0.1 GPa, while those values for aged samples at room temperature and 60 °C showed 38.8% and 51.3% losses, respectively. The hardness for the reference GE specimen was 0.189 ± 0.004 GPa, and after the aging process, it dropped by 2.1% (room temperature) and 27.51% (60 °C). Based on the continuous stiffness measurement for matrix cells, the mean value of modulus for the dry GE and CE matrix material cells was calculated as 4 GPa and 3.7 GPa, respectively. During the aging process, the hardness of CE samples decreased from 0.048 GPa to 0.038 GPa at room temperature and 60 °C, respectively, while aging of GE samples at both temperatures after 90 days caused a 31% loss in the hardness compared to the reference specimen. It was evident from the CSM experiments in the fibre constraint cells that the indentation modulus of the dry epoxy matrix constituent increased by 7.5% and 14% by the neighbouring stiff glass and carbon fibre regions respectively. The indentation characterization in GE samples thorough the standard method in the fibre constraint cells showed a 12.58% reduction in modulus at room temperature, and 25.8% at 60 °C compared to the reference specimen.

The Phase Transformation of Silicon Assessed by an Unloading Contact Pressure Approach

Silicon is of great economic importance for the semiconductor industry as well as of academic interest because of its high-pressure phase transformations. These transformations also occur during the indentation of silicon. To further investigate these transformations, a modified method using the continuous stiffness measurement (CSM) during unloading is presented in this work. The use of the CSM signal allows directly calculating the mean contact pressure while unloading. The measurements will be compared to conventional indentation tests and data from high-pressure cell experiments reported in the literature. Furthermore, the influence of constant load holding segments on the phase transformation during unloading is investigated.

Practical method to determine the effective zero-point of indentation depth for continuous stiffness measurement nanoindentation test with Berkovich tip

The zero-point of indentation depth in nanoindentation or depth-sensing instrumented indentation tests should be precisely set to evaluate the indentation hardness and indentation elastic modulus of materials to be tested, especially at shallow depths. A critical contact stiffness value has been widely used to determine the zero-point in nanoindentation tests with a Berkovich tip using the continuous stiffness measurement (CSM) method. However, this criterion occasionally gives an inadequate zero-point owing to the surface roughness of materials, the vibration of the testing system, and the flaws of the CSM method at shallow depth. This study proposes a practical method to determine the effective zero-point of indentation depth, which was obtained linearly at the zero-point of contact stiffness and extrapolated from the depth-dependent contact stiffness values, except for those at initially unstable contact depths. The proposed method enables nanoindentation tests to obtain a constant indentation elastic modulus and low deviation of nanoindentation hardness of homogenously fused silica and metallic materials, which provides an efficient way to obtain more accurate test data.

Tooth whitening, oxidation or reduction? Study of physicochemical alterations in bovine enamel using Synchrotron based Micro-FTIR

ObjectivesTooth whitening demand formulations have not evolved significantly over years being hydrogen peroxide (HP) or carbamide peroxide (CP) the main active agents used. These oxidizing compounds need high concentrations and long application times to achieve the desired whitening results, leading to painful secondary effects. A novel treatment based on a reducing agent, sodium metabisulphite (MBS) encapsulated in liposomes, demonstrated significant whitening results in just 3 minutes. The aim is to provide information about the chemical interactions of the encapsulated MBS with the enamel structure compared with CP’s and to study their penetration in the hydroxyapatite (HAP). MethodsChemical imaging is performed by synchrotron-based micro Fourier transformed infrared spectroscopy (SR-µFTIR). Continuous Stiffness Measurements (CSM) were used to determine the depth reached by the treatments in order to delimitate the area of study. ResultsPrincipal component analysis (PCA) showed that the main differences between treatments were found in the intensity of the ν3 PO3-4 peak related with tooth demineralization produced by the acidic nature of MBS; these changes were observed in deeper regions of the enamel when MBS was encapsulated. SignificanceThe obtained results indicated that CP and MBS promote different changes in the HAP mineral, and that liposomes favour the diffusion of MBS into the enamel. It is the first time that synchrotron light is used to map chemically the bovine incisor’s enamel, and to determine the effect of a whitening treatment in terms of chemical HAP modifications, and the extent in deep of these effects.

Continuous Stiffness Measurements and Nanoindentation Studies of bcc Mo: An Atomistic Approach

Continuous Stiffness Measurements and Nanoindentation Studies of bcc Mo: An Atomistic Approach

Quasi-static and dynamic depth-sensing indentation measurements to characterize wear and mar resistance of coating–polymer systems

Abstract Different layers of different thicknesses were coated on the same polymethyl methacrylate (PMMA) substrate. For each of these bilayered systems, quasi-static and dynamic instrumented indentations using continuous stiffness measurement have been made. We verified if data from indentation tests performed on a given sample obey a power law relationship. The aim was to calculate the viscoplasticity index n with sufficient accuracy (by taking into account the viscoelastoplastic properties of the studied samples), since this value is characteristic of the viscoplastic properties of a material and, therefore, allows evaluating the plastic scratch resistance of the surface. Thanks to both indentation methods the viscoplasticity index could be calculated and its value compared to the different bilayered systems one. As n is supposed to be intrinsic to a material, its value should not depend on the characterization technique.

Determination of the interfacial properties of carbon fiber reinforced polymers using nanoindentation

The mechanical properties of the interphase play a key role in determining the overall performance of carbon fiber reinforced polymer (CFRP) composite materials. For this reason, it is important to develop a method to easily and precisely investigate the mechanical performance of the interphase of CFRP materials. In this work, the surface topography of the CFRP material was examined using scanning probe microscopy (SPM), which revealed the polished flat sample can meet the requirements of the nanoindentation testing. The local mechanical performance of the interphase of the CFRP was determined using nanoindentation based on the continuous stiffness measurement (CSM) method. The results show that the size of the interphase between the carbon fiber and the matrix is about 1.5 μm, and the corresponding modulus and hardness values were estimated to be 5–11 and 0.4–3.3 GPa, respectively, considering the fiber-bias effects. Mapping of the local mechanical properties of a selected area revealed that nanoindentation reproduced excellently the surface topography and characterized precisely the properties of the interphase between the carbon fibers and the matrix.

Effect of indentation depth and strain rate on mechanical properties of Sn0.3Ag0.7Cu

In this paper, nanoindentation tests with continuous stiffness measurement (CSM) technique were conducted on Sn0.3Ag0.7Cu (SAC0307) at room temperature. The mechanical properties and creep behavior of SAC0307 under different indentation depths and strain rate were studied. Results show that SAC0307 alloy has good plastic deformation ability and the contact stiffness increases linearly with the depth of the indentation. Under different indentation depths and strain rates, the hardness of the material will be affected by the indentation size effect (ISE). Moreover, the hardness shows a certain strain rate sensitivity under the action of different strain rates. The elastic modulus of the material is almost constant with the increase of the indentation depth during the indentation process. But at lower indentation depth (hmax = 500 nm), the elastic modulus-displacement curve fluctuates greatly due to ISE affect. Based on the Nix-Gao model, the hardness (H0) of SAC0307 is 0.2GPa, and the micro characteristic length h⁎ is 867 nm. For the same holding time, creep deformation is more evident under high strain rate and indentation depths. The creep strain rate decrease with the increase of holding time and tends to a constant value.

Ferroelastic deformation mechanism and mechanical properties of [001]-oriented YSZ film by indentation

The ferroelastic properties of zirconia-based ceramics are crucial for their use as structural and functional materials. In this study, [001]-oriented ferroelastic YSZ films are prepared on the (100) SrTiO3 (STO) substrates by pulsed laser deposition (PLD). The mechanical properties and ferroelastic deformation mechanism of the film have been studied in detail through experiments and modeling. The Hardness and Young’s modulus of the YSZ film are 19.3 ± 0.4 GPa and 293.8 ± 5.1 GPa, respectively, which are determined by nanoindentation tests with the continuous stiffness measurement (CSM) mode. Indentation experiments show that a 90° twin domain structure is produced on the surface of the film. By combining TEM and STEM analysis methods, it was experimentally confirmed for the first time that the YSZ film produces ferroelastic deformation under the compressive stress of the indenter, causing the ferroelastic domain switching mechanism. Then the phase field simulation reproduced the ferroelastic domain switching process in the film under the indenter load and obtained the ferroelastic domain switching mechanism of the YSZ film. This proves the fundamental reason for the excellent mechanical properties of the ferroelastic YSZ film.

Enhanced creep resistance of Ti30Al25Zr25Nb20 high-entropy alloy at room temperature

Several previous studies have shown that the dissolution of Al in a solid solution single phase BCC is high unfavorable in TiZrNb system. In this work, a novel Ti30Al25Zr25Nb20 high-entropy alloy (HEA) with a single body-centered cubic (bcc) structure was developed. The Young's modulus and nano-hardness of this HEA measured by continuous stiffness measurement (CSM) technique were 158.2 ± 5.2 GPa and 8.9 ± 0.2 GPa, respectively. The creep behaviors of this HEA at a constant temperature of 20 °C under different loading rates and peak loads were studied by nano-indentation technique. The result indicated that with the increase of loading rates and peak loads, the creep displacement increased, but the creep strain rate sensitive index first decreased and then increased, and the physical mechanisms are interrupted by introducing dislocation activation volume. The reason might attribute to the hysteresis diffusion effect. Compared with other metallic structural materials, Ti30Al25Zr25Nb20 HEA possesses a relatively high dislocation activation volume and low creep strain rate sensitive index value, indicating a significantly high creep resistance.

Research on viscoelastic behavior of semi‐crystalline polymers using instrumented indentation

AbstractIn this study, the viscoelastic behavior of a polyamide 12 (PA12) polymer was evaluated using instrumented indentation technology based on a rheological model. The creep compliance and retardation spectra were obtained to analyze the viscoelastic response during the holding stage according to the rheological model under different preloading conditions. The results showed that the viscoelastic responses were independent of the indentation depth or load under step loading conditions. However, the creep compliance increases, and the peak intensity of the retardation spectrum decreases with a decrease in the preloading rate owing to the structural relaxation observed during the preloading stage under ramp loading conditions. Furthermore, softening dispersion can be completed during the loading stage under continuous stiffness measurement (CSM) conditions. As the preloading strain rate changes, the peak of the retardation spectrum gradually decreases until it disappears completely. Moreover, studies on indentation creep using the CSM method are challenging because of the complicated viscoelastic response observed during the preloading stage.