Li2O-Al2O3-SiO2微晶玻璃表面粗糙度对纳米硬度测试的影响

 介绍了纳米压痕测试技术的基础理论及纳米压痕法常用的Oliver -Pharr方法的计算原理。采用纳米压痕试验测得不同表面粗糙度的Li2O-Al2O3-SiO2微晶玻璃样品的纳米硬度、弹性模量和载荷-位移曲线。结果表明样品表面粗糙度会降低纳米压痕测试结果的稳定性、准确性和可靠性：样品表面粗糙度越小,测得的纳米硬度和弹性模量值波动越小,载荷-位移曲线重合性越高。随着最大载荷的增大,测得的弹性模量逐渐减小,其原因是压痕边缘材料发生了塑形变形。在超光滑表面样品（Ra=0.9 nm）上测得较为准确的Li2O-Al2O3-SiO2微晶玻璃纳米硬度和弹性模量值分别为8.8 GPa和7.79 GPa。纳米压痕测试结果的重合度对于评价超光滑表面完整性研究具有指导意义。     

Mechanical characteristics approach on W/Cr nano-interface structure

The objective of this article is to provide an experimental test and evaluation on mechanical characteristics of the W/Cr interface. The elastic modulus and hardness of the sample are measured by a nanoindentation tester. The test results show that the elastic modulus and hardness of the sample are nonlinear with respect to the depth h of the interface structure, unlike the usual approximate horizontal linear relationship as expected. To understand the bonding characteristics between W and Cr in nanoscale, the nano-scratch test is conducted considering the influence of thermal cycling load on the sample. The test results show that interfacial bonding strengths are different between samples under different thermal cycling loading conditions. It implies that the thermal loading has the potential probability to reduce the bonding reliability of the W/Cr interface. It builds a basis for future work of further investigations on mechanical properties of W/Cr interface structure.     

Nano-indentation Test and Numerical Evaluation of Cu–Cr Interface Structure in Micro/Nano Manufacturing

Interface design is an important topic in micro/nano electronic manufacturing. Interfaces of dissimilar materials in micro/nano electronic manufacturing are prone to crack initiations, leading to delaminations. The objective of this paper is to provide a systematic investigation to design or evaluate a bilayer film structure between Cu and Cr in micro/nano electronic manufacturing. In this paper, the Cu/Cr bilayer film prototype was deposited on the quartz glass by using RF magnetron sputtering. The elastic modulus and the hardness of the bilayer film prototype can be tested by using a nano-indenter. The test results show that the elastic modulus and the hardness of the bilayer film prototype are different at the difference maximum depth, h _max. The elastic modulus and the hardness of the Cu/Cr interface are influenced by the nanometer indentation size effect and each single film. The elastic modulus of the bilayer film shows nonlinear characteristics which include increase at first and decrease on second stage. The change trend of the hardness also shows nonlinear characteristics which include a fast steady decline at first and a slow nonlinear decline on second stage. These results show that there are scale domino effects in micro/nano electronic manufacturing. Based on the test results, the mechanical properties of the interface are not the simple average of each composition film. There is very great difference in the interface. In the meantime, the finite element method is used to simulate the plastic property of the interface. The comparison between the simulation and the test shows that the modeling method is a valid investigating method to analyze mechanical properties for nano-interface structure. It builds a basis for a progressive study of the mechanical properties of a Cu/Cr interface structure.     

Mechanical and microwave absorbing properties of carbon-filled polyurethane

Polyurethane (PU) matrix composites were prepared with various carbon fillers at different filler contents in order to investigate their structure, mechanical and microwave absorbing properties. As fillers, flat carbon microparticles, carbon microfibers and multiwalled carbon nanotubes (MWNT) were used. The microstructure of the composite was examined by scanning electron microscopy and transmission electron microscopy. Mechanical properties, namely universal hardness, plastic hardness, elastic modulus and creep were assessed by means of depth sensing indentation test. Mechanical properties of PU composite filled with different fillers were investigated and the composite always exhibited higher hardness, elastic modulus and creep resistance than un-filled PU. Influence of filler shape, content and dispersion was also investigated.     

高温高压下Zr2AlC的结构及热学性质的第一性原理

利用密度泛函理论研究了高温高压下Zr₂AlC的结构和热力学性质,计算得到Zr₂AlC的晶格参数与实验值符合较好．研究了Zr₂AlC的弹性常数、体模量、剪切模量和杨氏模量等力学性质随压力变化的趋势．同时研究了维氏硬度随压力的变化趋势．通过计算得到的杨氏模量预测了Zr₂AlC的弹性各向异性．最后,基于准简谐德拜模型,成功预测了Zr₂AlC的德拜温度、热容、热膨胀系数和Grüneisen参数随着压强和温度的变化关系.     

Composition, structure, and properties of tantalum boride nanostructured films

The structure, as well as the phase and elemental compositions, of tantalum diboride-based nanostructured films deposited by rf magnetron sputtering under various conditions are studied by X-ray diffraction, electron microscopy, and secondary ion mass spectrometry. The physicomechanical properties of the films (hardness, as well as elastic and plastic properties) are determined. The maximum hardness and elastic modulus of the synthesized films are 42 are 240 GPa, respectively. The grain size is found to influence the physicomechanical and electrical properties of the films.     

On the uniqueness and sensitivity issues in determining the elastic and plastic properties of power-law hardening materials through sharp and spherical indentation

A systematic study of the uniqueness, reversibility and sensitivity issues associated with seven indentation-based methods of property extraction demonstrates that: (i) The indentation algorithms generally identify the elastic and plastic properties of materials uniquely for most materials. (ii) The indentation forward algorithms (wherein the indention responses are determined from the elastic and plastic properties of the indented materials) and the reverse algorithms (wherein the elastic and the plastic properties of materials are extracted from the indentation responses) are distinct for each indentation method and are internally consistent in that the differences in the elastic and plastic properties determined through the reverse analysis and the ‘true’ material properties are generally small for a large number of materials, for each of the seven methods. (iii) While the differences in the indentation response parameters predicted by each of the seven indentation methods (for a particular material) could be small, there could be considerable dispersion in the elastic and plastic properties predicted by the reverse algorithms of the seven methods (for a particular set of indentation response parameters). (iv) In the forward analysis, small uncertainties in the elasto-plastic properties lead to small uncertainties in the predictions of the indentation response of materials. The sensitivity distribution is generally heterogeneous and symmetric across positive and negative variations in the material elasto-plastic properties. (v) In the reverse analysis, the elastic modulus exhibits low sensitivity, while the yield strength and the strain-hardening exponent generally exhibit high sensitivity to uncertainties in the indentation response parameters. The sensitivity distribution is heterogeneous and asymmetric across positive and negative variations in the indentation response parameters. (vi) The representative stresses are fairly robust to uncertainties in the indentation response parameters. Consequently, dual sharp and spherical indentation methods, which identify multiple representative stresses, exhibit reduced sensitivity in the determination of the plastic properties.     

Mechanical and dynamical stability of TiAsTe compound from ab initio calculations

The first-principles calculations are employed to provide a fundamental understanding of the structural features and relative thermodynamical, mechanical and phonon stability of TiAsTe compound. The calculated lattice parameters are in good agreement with available experimental results. We have computed elastic constants, its derived moduli and ratios that characterize mechanical properties for the first time. The calculated elastic constants indicate that these materials are mechanically stable at ambient condition. The minimum thermal conductivities of TiAsTe are calculated using both Clarke’s model and Cahill’s model. Furthermore, the elastic anisotropy has been visualized in detail by plotting the directional dependence of compressibility, Young’s modulus and shear modulus. Our results suggest strong elastic anisotropy for this compound. Additionally, the phonon spectra and phonon density of states are also obtained and discussed. The full phonon dispersion calculations confirm the dynamic stability of TiAsTe.     

Nanoindentation of gold nanoparticles functionalized with proteins

The hardness and Young's modulus of 10 and 20 nm gold nanoparticles (Au NPs) modified with bovine serum albumin and streptavidin were measured using a nanoindenter. The Au NPs were immobilized on a semiconductor surface through organic self-assembled monolayers. Changes in mechanical properties occurred when the Au NPs were immobilized on the surface. The hardness and Young's modulus were dependent on the size of the NPs, and the proteins on the particles showed highly plastic and elastic behavior compared to flat surfaces modified with self-assembled monolayers.     

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.     

Band parameters of α-LiBeN semiconductor from density functional calculations

The structural, elastic, electronic, optical and thermal properties of α phase in LiBeN semiconductor have been studied using pseudo-potential plane wave method based on the density functional theory. The computed lattice parameter agrees well with previous theoretical work. The elastic constants and their pressure dependence are predicted using the static finite strain technique. A set of isotropic elastic parameters and related properties, namely bulk and shear moduli, Young’s modulus, Poisson’s ratio, average sound velocity and Debye temperature are numerically estimated in the frame work of the Voigt–Reuss–Hill approximation for α-LiBeN polycrystalline aggregate. The assignments of the structures in the optical spectra and band structure transitions have been examined and discussed. The thermal effect on heat capacities is investigated by the quasi-harmonic Debye model. To the best of our knowledge, most of the studied properties of the material of interest are reported for the first time.     

LY-12铝高温凝聚态动力学性质研究——高温弹性模量的测定

 金属材料的高温动态力学性能是材料科学领域中的重要方面。本文介绍LY-12合金铝在常温至450 ℃的温度区间内和动载下（应变率为10³/s），材料弹性模量的研究。此项研究采用的试验装置为一维Hopkinson压杆及管式高温炉。应用一维弹性应力波传播理论，测得LY-12铝试件在不同温度T条件下的声速c(T)，按照c(T)=[E(T)/ρ(T)]^1/2，获得杨氏模量E(T)随温度的变化曲线。     

Mechanical characteristics of Fe-based coating obtained by nanoindentation

In this study, clad layers of iron-based alloy with a nature of self-fluxing were melted on low carbon steel by plasma cladding process. Nanoindentation with atomic force microscopy (AFM) has been used to investigate the mechanical properties of the coating. Hardness and elastic modulus at ultra-low loads were first determined using the method proposed by Giannakopoulos and Suresh (G&S method). The true contact area and mechanical properties were then determined using atomic force microscopy (AFM) combined with the Oliver and Pharr method (new proposed method) as the correction group. The mechanical properties calculated by the two methods showed the same distribution while had deviation in specific values. The effect of surface roughness to the calculated mechanical properties was investigated. Both hardness and elastic modulus were found to exhibit certain surface roughness dependence. When root mean square (RMS) roughness ranged from 2.2 nm to 4.4 nm, hardness calculated by both the methods increased obviously and reached maximums around 4.1 nm. Elastic modulus calculated by G&S method at different RMS showed the same distribution with that of hardness, while reduced elastic modulus obtained by AFM was insensitive to the range of RMS.     

Anisotropic elastic properties of MB (M = Cr,Mo, W) monoborides: a first-principles investigation

First principles calculations were performed to systematically investigate structure properties, phase stability and mechanical properties of MB (M = Cr, Mo, W) monoborides in orthorhombic and tetragonal structures. The results of equilibrium structures are in good agreement with other available theoretical and experimental data. The elastic properties, including bulk modulus B, shear modulus G, Young’s modulus E and Poisson’s ratio ν were calculated by the Voigt-Reuss-Hill approximation. All considered monoborides are mechanically stable. The results of elastic anisotropies show that elastic anisotropy of orthorhombic structure is larger than that of tetragonal structure. Moreover, the minimum thermal conductivities were also estimated using the Cahill’s model, and the results indicate that the minimum thermal conductivities show a dependence on directions.     

Ground-State Structure and Physical Properties of NB_2 Predicted from First Principles

Using the newly developed particle swarm optimization algorithm on crystal structural prediction,we predict a new class of boron nitride with stoichiometry of NB_2 at ambient pressure,which belongs to the tetragonal I4m2 space group.Then,its structure,elastic properties,electronic structure,and chemical bonding are investigated by first-principles calculations with the density functional theory.The phonon calculation and elastic constants confirm that the predicted NB_2 is dynamically and mechanically stable,respectively.The large bulk modulus,large shear modulus,large Young's modulus,and small Poisson's ratio show that the I4m2 NB_2 should be a new superhard material with a calculated theoretical Vickers hardness value of 66 GPa.Further analysis on density of states and eiectron localization function demonstrate that the strong B-B and B-N covalent bonds are the main reason for its high hardness in I4m2 NB_2.     

Experimental approach on interfacial properties for Cr/Al double nanometer films under different temperature environment mode

In this paper, a typical interfacial structure sample between the materials Cr and Al was fabricated. To investigate the interfacial characteristics, the mechanical properties of the Cr/Al double interfacial structure were tested using the nanoindenter and the nanoscratch. The test results show that both of the values are easily influenced by the different depth h. In the nanoscratch experiment, the bilayer films are set off as two groups, one of which is tested after the thermal cycling load while the other is not. The test results show that the interface formation and the binding force in the interface can be easily influenced by the difference thermal characteristic of the each single film. The elastic modulus and the hardness of the bilayer films are investigated using the nanoindentation.     

动态柱形空穴膨胀模型及其在侵彻问题中的应用

 在侵彻问题中的应用进行了研究。通过采用相似变换求解塑性区控制方程,获得了动态柱形空穴膨胀中的弹塑性界面速度、径向应力分布、空穴表面应力的解。基于柱形空穴模型,推导了侵彻方程,并将其得到的预测结果与侵彻实验数据进行了比较。结果表明,模型的理论解与现有数据吻合得很好。 结果还显示了材料的可压缩性和塑性强化模量对柱形空穴膨胀以及侵彻阻力的影响。     

Accelerating inverse crystal structure prediction by machine learning: A case study of carbon allotropes

Based on structure prediction method, the machine learning method is used instead of the density functional theory (DFT) method to predict the material properties, thereby accelerating the material search process. In this paper, we established a data set of carbon materials by high-throughput calculation with available carbon structures obtained from the Samara Carbon Allotrope Database. We then trained a machine learning (ML) model that specifically predicts the elastic modulus (bulk modulus, shear modulus, and the Young’s modulus) and confirmed that the accuracy is better than that of AFLOW–ML in predicting the elastic modulus of a carbon allotrope. We further combined our ML model with the CALYPSO code to search for new carbon structures with a high Young’s modulus. A new carbon allotrope not included in the Samara Carbon Allotrope Database, named Cmcm–C24, which exhibits a hardness greater than 80 GPa, was firstly revealed. The Cmcm–C24 phase was identified as a semiconductor with a direct bandgap. The structural stability, elastic modulus, and electronic properties of the new carbon allotrope were systematically studied, and the obtained results demonstrate the feasibility of ML methods accelerating the material search process.     

Effects of surface charges on phonon properties and thermal conductivity in GaN nanofilms

Surface charges can modify the elastic modulus of nanostructure, leading to the change of the phonon and thermal properties in semiconductor nanostructure. In this work, the influence of surface charges on the phonon properties and phonon thermal conductivity of GaN nanofilm are quantitatively investigated. In the framework of continuum mechanics,the modified elastic modulus can be derived for the nanofilm with surface charges. The elastic model is presented to analyze the phonon properties such as the phonon dispersion relation, phonon group velocity, density of states of phonons in nanofilm with the surface charges. The phonon thermal conductivity of nanofilm can be obtained by considering surface charges. The simulation results demonstrate that surface charges can significantly change the phonon properties and thermal conductivity in a GaN nanofilm. Positive surface charges reduce the phonon energy and phonon group velocity but increase the density of states of phonons. The surface charges can change the size and temperature dependence of phonon thermal conductivity of GaN nanofilm. Based on these theoretical results, one can adjust the phonon properties and temperature/size dependent thermal conductivity in GaN nanofilm by changing the surface charges.