铁基块体非晶合金在纳米压痕过程中的蠕变行为研究

利用纳米压痕技术研究了{［（Fe_0.6Co_0.4）_0.75B_0.2Si_0.05］_0.96Nb_0.04}₉₆Cr₄铁基块体非晶合金的室温蠕变行为及不同的加载速率对该块体非晶合金蠕变变形的影响.{［（Fe_0.6Co_0.4）_0.75B_{0.2< 关键词： 块体非晶合金 蠕变 EVEV模型 蠕变速率敏感指数}     

Nanoindentation study of size effect and loading rate effect on mechanical properties of a thin film metallic glass Cu49.3Zr50.7

A binary metallic glass (MG) Cu_49.3Zr_50.7 in the form of thin film was successfully grown on a Si (1 0 0) substrate by magnetron sputtering. The mechanical properties, specifically, hardness and modulus at various peak loads and loading rates were characterized through instrumented nanoindentation. Unlike other metallic glasses showing an indentation size effect (ISE), the composition of this study does not have an ISE, which is phenomenologically the result of the negligible length scale according to the strain gradient plasticity model. The proportional specimen resistance model is applicable to the load-displacement behaviors and suggests that the frictional effect is too small to contribute to the ISE. The occurrence of plasticity depends on loading rates and can be delayed so that the displacement during the load holding segment increases logarithmically. In addition, the hardness and modulus are both dependent on the loading rates as well, i.e., they increase as the loading rate increases up to 0.1 mN/s and then hold constant, which is independent of creep time (≤100 s). These loading-rate-dependent behaviors are interpreted as the result of viscoelastic effect rather than free volume kinetics.     

Size effects of the strength and elastic properties of individual phases and interphase boundaries of polycrystalline materials

Size effects of hardness are studied and numeric values of Young’s modulus E, hardness H, and fracture toughness coefficient K_c of individual phases and interphase boundaries of polycrystalline samples of ferruginous quartzite are determined by means of micro- and nanoindentation methods. It is found that the interphase boundary of magnetite and hematite is the one most strengthened, while the boundary of the hematite and quartz is the one least durable.     

Indentation Load Effect on Young＇s Modulus and Hardness of Porous Sialon Ceramic by Depth Sensing Indentation Tests

Depth sensing indentation （DSI） tests at the range of 200-1800mN are performed on porous sialon ceramic to determine the indentation load on Young＇s modulus and hardness values. The Young modulus and hardness （Dynamic and Martens） values are deduced by analysing the unloading segments of the DSI test load-displacement curves using the Oliver-Pharr method. It is found that Young＇s modulus ET, the dynamic hardness HD and the Martens hardness HM exhibit significant indentation load dependences. The values of Young＇s modulus and hardness decrease with the increasing indentation load, as a result of indentation load effect. The experimental hf /hm ratios lower than the critical value 0.7, with hm being the maximum penetration depth during loading and hf the final unloading depth, indicate that our sample shows the work hardening behaviour.     

Identification of elastic-plastic and phase transition characteristics for relaxor ferroelectric PMN-PT anisotropic single crystals using nanoindentation technique

As one kind of important ferroelectric ceramics, relaxor ferroelectric PMN-PT single crystals have triggered a revolution in electromechanical devices owing to their giant piezoelectric properties and ultra-high electromechanical coupling factors. The present study focused on the mechanical responses of [100]- and [110]-oriented poled PMN-PT ferroelectric single crystals under an indenter loading. The hardness and Young’s modulus with different crystallographic orientations of the crystals were measured by using the continuous stiffness measurement (CSM) with nanoindentation technique. Using a spherical indenter pressured at different indentation depths, the typical quasi-static nanoindentation tests with displacement-controlled mode were performed on the PMN-PT single crystal samples. Load–displacement curves of indentations were recorded to reveal the yielding or inelasticity behaviour in [100]- and [110]-oriented PMN-PT through a pop-in event. It was further verified by the stress–strain curves evaluated from the corresponding load–displacement curves, to show the similar characteristic on the elastic–inelastic transition. When a Berkovich indenter was employed for mechanical response testing, another pop-in event was observed at a smaller indentation depth compared to the one for elastic–inelastic transition, which may indicate a pressure-induced phase transition from rhombohedral (R) to tetragonal (T) of the PMN-PT single crystals.     

Nanoindentation of a hard ceramic coating formed on a soft substrate

The hardness and Young’s modulus of the thin hydroxyapatite-based coatings deposited by RF magnetron sputtering onto magnesium alloy, titanium, and steel substrates are studied. As the penetration depth increases, the hardness and Young’s modulus of these coatings are found to tend toward the values that are characteristic of the substrates. It is shown that the difference between the values of hardness and Young’s modulus at small penetration depths (h < 80–100 nm) can be caused by the difference between the physicomechanical properties inside the coatings and that this difference at large penetration depths (h > 100 nm) can be induced by an additional effect of the strength properties of the substrate material.     

Correlation between structural and mechanical properties of PbTiO3 thin films grown by pulsed-laser deposition

Tetragonal lead titanate (PbTiO₃, PT) thin films are grown on (1 0 0) MgO substrate by pulsed-laser deposition (PLD) for expected applications in integrated optics. The realisation of outstanding and reliable devices into integrated circuits requires sufficient mechanical resistance despite that the obtained PT films display interesting waveguiding properties associated with low optical losses. Two mechanical properties characteristic of elasticity and hardness of PT films are studied. The elastic modulus (E or Young's modulus) and the hardness (H) are measured by the nanoindentation technique. These mechanical properties are correlated to the crystalline quality of PT/MgO thin films. The films show epitaxial relationship with the MgO substrate and the orientation of crystallites perpendicularly to the surface substrate may be the consequence of a growth process along c-axis, a-axis or both. Differences on curves plotting hardness and elastic modulus as a function of indentation depth are observed as the curves are less dispersed for the films mainly c-axis oriented.     

Experimental study of room-temperature indentation viscoplastic ‘creep’ in zirconium

In this paper we have studied the mechanisms of so-called ‘indentation creep’ in a zirconium alloy. Nanoindentation was used to obtain strain rate data as the sample was indented at room temperature, at a homologous temperature below that for which creep behaviour would be expected for this material. A high value of strain rate was obtained, consistent with previous work on indentation creep. In order to elucidate the mechanism of time-dependent deformation, a load relaxation experiment was performed by uniaxial loading of a sample of the same alloy. By allowing relaxation of the sample from a peak load in the tensile test machine, a similar stress exponent was obtained to that seen in the nanoindentation creep test. We conclude that for metals, at temperatures below that at which conventional creep will occur, nanoindentation ‘creep’ proceeds through deformation on active slip systems that were initiated by prior loading beyond the plastic limit. It is therefore more appropriate to describe it as a viscoplastic process, and not as creep deformation.     

Theoretical study on nanoindentation hardness measurement of a particle embedded in a matrix

The finite element method was used to simulate indentation tests on a particle embedded in a matrix, to investigate the influence of the properties of the particle and the matrix, and the indentation depth on the measured hardness. The particle’s work-hardening exponent and the mismatch in particle and matrix yield strength have a significant influence on the measured hardness. A particle-dominated indentation depth was identified, within which the measured nanoindentation hardness agrees very well with the true hardness of the particle material. Numerical results from the simulations of a wide range of material properties determined that the measured hardness is within 5% difference of the particle’s true hardness when the indentation depth is less than 13.5% of the particle’s radius. The results can be used in practice as a guideline to measure the hardness of a particle embedded in a matrix and provides the theoretical basis to develop a particle-embedded method to measure the hardness of individual particles.     

Nanoindentation of amorphous Ge-As-Se films

Changes in the nanohardness H and Young’s modulus E of Ge _x As _y Se_{100 ? x ? y} films have been studied as a function of the penetration depth of the Berkovich indenter. The values of H and E have been measured in the regime of harmonic modulation of a linearly increasing indenter load. It has been shown that the changes in E and H of the films under study during nanoindentation arise due to the peculiarities of their elastoplastic behavior, the formation of deformation zones near the nanocontact, and also size effects.     

Design and fabrication of single-crystal GaN nano-bridge on homogeneous substrate for nanoindentation

This study reports a simple method to design and fabricate a freestanding GaN nano-bridge over a homogeneous short column as supporting leg. Test samples were fabricated from MOCVD-grown single-crystal GaN films over sapphire substrate using a FIB milling to leave freestanding short spans. We also investigated the nanoindentation characteristics and the corresponding nanoscopic mechanism of the GaN nano-bridge and its short column with a conical indenter inside transmission electron microscopy. The stress–strain mechanical properties and Young’s modulus have also been examined and calculated as 108 GPa ± 4.8 % by the strain energy method. The significant slope switch of the L–D curve corresponds to the transition from the single-point bending indentation to the surface stretching indentation and has been interpreted with the evolution of TEM images. This freestanding fabrication and test have key advantages to characterize nanoscale behavior of one-dimensional bridge structure and greater ease of sample preparation over other micro-fabrication techniques.     

Nanomechanical characteristics of SnO2:F thin films deposited by chemical vapor deposition

The nanoindentation characterizations and mechanical properties of fluorine-doped tin oxide (SnO₂:F) films deposited on glass substrates, using chemical vapor deposition (CVD) method, were studied, which included the effects of the indentation loads, the loading time and the hold time on the thin film. The surface roughness, fractal dimension and frictional coefficient were also studied by varying the freon flow rates. X-ray diffraction (XRD), atomic force microscopy (AFM) and frictional force microscopy (FFM) were used to analyze the morphology of the microstructure. The results showed that crystalline structure of the film had a high intensity (1 1 0) peak orientation, especially at a low freon flow rate. According to the nanoindentation records, the Young's modulus ranged from 62.4 to 75.1 GPa and the hardness ranged from 5.1 to 9.9 GPa at a freon flow rate of 8000 sccm. The changes in measured properties were due to changing loading rate.     

Investigation of the local mechanical properties of potassium chloride single crystals by atomic force microscopy

Using an atomic force microscope (AFM), the of hardness H and Young’s modulus E are measured in near-surface layers of KCl single crystals to a depth of 300 nm at loads of 5–100 µN. The values of H and E are estimated indirectly by analyzing P(h) curves (load vs. indentation depth curves). The value of H is also estimated directly by measuring the area of an indentation with the help of an AFM with a nanoscale resolution. The effect of structural features of the surface around an indentation on the accuracy of the H and E estimates is revealed. The sharp dependence of H on the load (the nanoscale effect) is revealed. The experimental results agree qualitatively with the predictions of the geometrically necessary dislocation model developed by Nix and Gao. However, in order to quantitatively estimate mass transfer from a nanoindenter, a structural analysis is required with allowance for plastic deformation in crystals.     

First-principles investigation of the equation of state and elastic properties of perovskite-type SrW(O,N)<Subscript>3</Subscript> under hydrostatic pressures up to 139 GPa

Pressure dependence of the structural and elastic properties of perovskite-type cubic SrWO_2.05N_0.95 was studied using firstprinciples density functional theory (DFT) utilizing the plane wave pseudopotential and the exchange-correlation functionals within the generalized gradient approximation. The estimated bulk modulus and its pressure derivative values from the P ? V data fitted to the third-order Birch-Murnaghan equation of state were close to the data obtained from the independent elastic constants. Based on the generalized Born stability criteria, SrWO_2.05N_0.95 is mechanically stable up to 139 GPa. The influence of hydrostatic pressure (0 to 139 GPa) on the bulk modulus, shear modulus, Young’s modulus, Pugh’s modulus ratio, Poisson’s ratio, Vickers hardness, sound velocities, Debye temperature, Debye-Grüneisen parameter, minimum thermal conductivity and elastic anisotropy of SrWO_2.05N_0.95 was particularly studied in detail. It was found that SrWO_2.05N_0.95 is a ductile and hard solid with large bulk, shear and Young’s modulus and displays an extraordinary low thermal conductivity. Since there are not any experimental or theoretical data available for comparison the results of the present study have revealed an important fundamental information about the elastic properties of perovskite-type cubic SrWO_2.05N_0.95 for future experimental studies.     

Effect of alternating electric current on the nanoindentation of copper

Electromechanical interaction determines the structural reliability of electronic interconnects. Using the nanoindentation technique, the effect of alternating electric current on the indentation deformation of copper strips was studied for the indentation load in a range of 100 to 1600???N at room temperature. During the test, an alternating electric current of the electric current density in a range of 1.25 to 4.88?kA/cm² was passed through the copper strips. The indentation results showed that the reduced contact modulus decreased linearly with increasing the electric current density. The indentation hardness decreased with increasing the indentation deformation, demonstrating the normal indentation size effect. Using the model of strain gradient plasticity, we found that the strain gradient underneath the indentation decreased slightly with increasing the electric current density for the same indentation depth.     

A displacement sensing nanoindentation study of tribo-mechanical properties of the Ni-Co system

An analysis of the tribo-mechanical properties of the Ni-Co system, at the submicrometric contact scale, is conducted using displacement sensing nanoindentation. In particular, the influence of contact depth and surface finishing methods on the hardness, H, and Young's modulus, E, of the materials is analysed. Mechanically and electrolitically polished samples were tested with a conospherical indenter using a range of loads between 0.05 and 10 mN. It is shown that the hardness of these materials depends on the surface finishing method and increases with decreasing contact depth, while the Young's modulus is relatively insensitive to contact depth. Furthermore, sample polycrystallinity leads to a large scattering of hardness values in Co-rich samples and of Young's modulus values in Ni-rich ones. The combined parametric ratio H/E, which can be related to the tribological behaviour of the material, was found to be higher in samples with Co content larger than 80 wt.%.     

Influence of germanium incorporation on the structural and electrical properties of boron-doped ultrathin poly-Si1−x Ge x films deposited by chemical vapour deposition

A few properties of polycrystalline silicon germanium (poly-Si_1?x Ge _x ) films can be tailored by modulating the germanium incorporation. In this paper, the structural, mechanical and electrical properties of heavily doped ultrathin (~100 nm) poly-Si_1?x Ge _x films (0.84 ≤ x ≤ 0.88) fabricated by low-pressure chemical vapour deposition were investigated. For a boron concentration of ~2.2 × 10²¹ atoms/cm³, a slight increase of germanium fraction significantly enhances the deposition rate, crystallinity and Hall mobility while having negligible influence on the Young’s modulus and hardness. The grain size increases from ~6 to ~12 nm while the grain structure becomes more columnar. In addition, the resistivity decreases from 7.4 to 1.1 m Ω cm with a corresponding increase in the Hall mobility from ~0.9 to ~4.2 cm² V^?1 s^?1. However, the Young’s modulus (~101 GPa) and hardness (~8.8 GPa) are virtually unaffected within the range of germanium fraction explored. In practice, poly-SiGe layer having low resistivity, high modulus, high mobility and low surface roughness can be successfully applied for resonators, biosensors and nanoswitches among others.     

AFM as an alternative for Young’s modulus determination in ceramic materials in elastic deformation regime

A novel alternative to the conventional nanoindentation technique for hard materials is presented. An atomic force microscopy probe is used as an indenter, applying loads in the nN range and producing elastic deformations of a few nanometres. This new technique allows a reduction of the different inherent nanoindenter problems. This result in an increase in the quality of the overall results, and thus provide better understanding of the contact mechanism between the indenter and the sample, yielding Young’s modulus values consistent with the literature. This is confirmed by a series of experiments performed on different YBa₂Cu₃O_7?x textured and single crystal samples textured using different techniques.     

The structure and mechanical properties of thick rutile-TiO2 films using different coating treatments

The hardness and Young's modulus of thick rutile-TiO₂ films were determined using a continuous stiffness measurement (CSM) technique in this study. Pure rutile-TiO₂ nanopowders (TH₂O, TFeSO₄ and TCuSO₄) were prepared using a modified homogeneous-precipitation process at low temperature (MHPPLT) method. The TiO₂ films were prepared from sols using 3% (w/w) of the prepared-TiO₂ suspension solution coated onto silicon wafers. After dip-coating was completed, the coatings were further treated by natural air-drying, water-vapor exposure, and calcination, respectively. An ellipsometry with a monochromator was used to measure the thickness and refractive index of the TiO₂ films, and a scanning electron microscopy (SEM) to determine their morphology. Three coatings of TH₂O, TFeSO₄ and TCuSO₄ demonstrated their refractive indexes of around 1.60 under three treatments. Volumetric expansion and thickness of the coatings should influence their refractive index. Furthermore, the continuous stiffness measurement (CSM) technique was used to perform nanoindentation testing on the hardness and Young's modulus of prepared rutile-TiO₂ coatings. The mean hardness and Young's modulus of three coatings increased with preparation temperature. In addition, the TH₂O coatings demonstrated greater hardness and modulus than those of TFeSO₄ and TCuSO₄ coatings in the natural air-drying condition. Surface cracking observed on the calcinated TFeSO₄ should be the reason why an obvious decrease of the mean hardness and Young's modulus appeared. Finally, two mechanical properties and related nanoindentation depth of the coatings were discussed in detail.     

Molecular dynamic simulations of nanoindentation in aluminum thin film on silicon substrate

In the present work, the nanoindentation of aluminum thin film on silicon substrate is investigated by three-dimensional molecular dynamic (MD) simulation. The film/substrate system is modeled by taking Lennard-Jones (LJ) potential to describe the interaction at the film-substrate interface. Different loading rate from 50 to 250 m/s is carried out in the simulation. The results showed that the hardness of the film increased with the loading rate. In order to study the effect of substrate on the mechanical properties of thin film, nanoindentation process on monolithic Al material is also simulated. The simulation results revealed that indentation pile-up in the aluminum film is significantly enhanced by the substrate. The substrate also affects the loading force during the nanoindentation. At the beginning of the indentation, the loading force is not affected by the substrate. Then, it is getting smaller caused by the interface. As the film is penetrated, the loading force increased rapidly caused by the hard substrate. These results were coincident with the previous reported experiments.