Nanomechanical characterization of cement-based pastes enriched with SiO2 nanoparticles

Microstructural and nanomechanical surface properties of cement based pastes were experimentally investigated. Samples were prepared from CEMI42.5 cement, with water to cement ratio equal to 0.5 and enriched with SiO₂ nanoparticles (d = 14 nm), with low concentration ranging from 0% up to 0.5% (by weight of binder). X-rays diffraction (XRD) patterns revealed a linear increase of crystal size of calcium hydrate (CH) products with the addition of nanoparticles, while scanning electron microscopy (SEM) images showed a denser microstructure with more defined grains for the higher SiO₂ nanoparticles concentration. Atomic force microscopy (AFM) studies of samples after the grinding/polishing process indicated a strong dependence of surface roughness with the CH crystallite mean size and the materials mechanical properties. Finally, statistical analysis of nanoindentation mapping data revealed a decrease of elastic modulus with the increase of nanoparticles concentration.     

Structural changes of hot-wire CVD silicon carbide thin films induced by gas flow rates

Silicon carbide (SiC) thin films were prepared by hot-wire chemical vapor deposition in a CH₄ gas flow rate of 1 sccm, and the influence of the gas flow rates of SiH₄ and H₂ gases on the film structure and properties were investigated. In the case of a H₂ gas flow rate below 100 sccm, the SiC:H films obtained in SiH₄ gas flow rates of 3 and 4 sccm were amorphous. On the other hand, when the H₂ gas flow rate was above 150 sccm, SiH₄ gas flow rates of 4 and 3 sccm resulted in a Si-crystallite-embedded amorphous SiC:H film and a nanocrystalline cubic SiC film, respectively. It was found that gas flow rates were important parameters for controlling film structure.     

Nanomechanical properties of friction stir welded AA6082-T6 aluminum alloy

Lightweight alloys are of major concern, due to their functionality and applications in transport and industry applications. Friction stir welding (FSW) is a solid-state welding process for joining aluminum and other metallic alloys and has been employed in aerospace, rail, automotive and marine industries. Compared to the conventional welding techniques, FSW produces joints which do not exhibit defects caused by melting. The objective of the present study is to investigate the surface hardness (H) and elastic modulus (E) in friction stir welded aluminum alloy AA6082-T6. The findings of the present study reveal that the welding process softens the material, since the weld nugget is the region where the most deformations are recorded (dynamic recrystallization, production of an extremely fine, equiaxial structure), confirmed by optical microscopy and reduced nanomechanical properties in the welding zone. A yield-type pop-in occurs upon low loading and represents the start of phase transformation, which is monitored through a gradual slope change of the load-displacement curve. Significant pile-up is recorded during nanoindentation of the alloy through SPM imaging.     

Nanomechanical characterization of thermally evaporated Cr thin films — FE analysis of the substrate effect

We study the substrate effect on the deformation and hardness behaviour of chromium thin films using nanoindentation technique. Two different substrates namely Si (100) and AISI-304 SS are used in order to obtain a soft film on a hard substrate and a hard film on a soft substrate combination. Typical hardness variations for the two combinations are obtained. It is also observed that Cr thin films deposited on two different substrates deform distinctly. Radial cracks are found to develop in the case of Cr film on Si whereas circumferential cracks are produced in the case of Cr film on SS substrate. Using 2-D finite element analysis, it is found that the substrate not only affects the development of plastic zone but also the stress distribution in the films which results in observed distinct hardness and deformation behaviour.     

Frictional contact of flexible and rigid bodies

 This paper is about planar frictional contact problems of both flexible and rigid bodies. For the flexible case a nonlinear finite element formulation is presented, which is based on a modified Coulomb friction law. Stick-slip motion is incorporated into the formulation through a radial return mapping scheme. Linearly interpolating four node elements and three node contact elements are utilized for the finite element discretization. The corresponding tangent stiffness matrices and residual vectors of the equations of motion are presented. In the rigid body case the contact problem is divided into impact and continual contact, which are mathematically described by linear complementarity problems. The impact in normal direction is modeled by a modified Poisson hypothesis, which is adapted to allow multiple impacts. The formulation of the tangential impact is grounded on Coulombs law of friction. The normal contact forces of the continual contact are such that colliding bodies are prevented from penetration and the corresponding tangential forces are expressed by Coulombs law of friction. Examples and comparisions between the different methods are presented. Received: 10 January 2001     

ZnO based third generation biosensor

Zinc oxide (ZnO) has emerged as a leading material in the field of biosensors. However, the absence of redox couple is proving to be the major hindrance towards the development of a ZnO based third generation biosensor. Development of a composite matrix can be a possible way towards the realization of ZnO based mediator-less biosensor. In the present work pulsed laser deposition, chemical method and ion implantation has been explored for realization of ZnO based matrix which can be exploited for biosensor applications in mediator-free environment.     

Deposition and characterization of magnetron sputtered amorphous Cr-C films

Thin films in the Cr-C system with carbon content of 25-85 at.% have been deposited using non-reactive DC magnetron sputtering from elemental targets. Analyses with X-ray diffraction and transmission electron microscopy confirm that the films are completely amorphous. Also, annealing experiment show that the films had not crystallized at 500 °C. Furthermore, X-ray spectroscopy and Raman spectroscopy show that the films consist of two phases, an amorphous CrC_x phase and an amorphous carbon (a-C) phase. The presence of two amorphous phases is also supported by the electrochemical analysis, which shows that oxidation of both chromium and carbon contributes to the total current in the passive region. The relative amounts of these amorphous phases influence the film properties. Typically, lower carbon content with less a-C phase leads to harder films with higher Young’s modulus and lower resistivity. The results also show that both films have lower currents in the passive region compared to the uncoated 316L steel substrate. Finally, our results were compared with literature data from both reactively and non-reactively sputtered chromium carbide films. The comparison reveals that non-reactive sputtering tend to favour the formation of amorphous films and also influence e.g. the sp²/sp³ ratio of the a-C phase.     

Nanoindentation behavior of bulk metastable Al65Cu20Ti15 alloy prepared by consolidation of the ball milled powder

Present study concerns assessment of nanomechanical property in the bulk Al₆₅Cu₂₀Ti₁₅ alloy with varying microstructure synthesized by consolidation of mechanically alloyed powder at different temperature. The microstructure after consolidation at room temperature and 500 °C exhibits completely amorphous and nanocrystalline states respectively. Nanoindentation experiments suggest that the maximum strength and hardness values are achieved in the sample sintered at 450 °C. The corresponding microstructure revealed dispersion of nanocrystalline intermetallic phase (<50 nm) in the amorphous matrix.     

Effect of Alumina Dispersion on Microstructural and Nanomechanical Properties of Pulse Electrodeposited Nickel-Alumina Composite Coatings

Nickel-gamma alumina（Ni—γAI2O3） composite coatings were synthesized by pulsed electrodeposition technique with different concentrations of alumina（0,10,20 and 50 g/L） in Watt’s bath.Both ultrasonic vibration and magnetic-stirring were utilized to disperse Al2O3 and to achieve its optimum loading.Microstructure shows that agglomerates occur at higher loadings,but 10 g/L Al2O3 addition in bath has shown uniform dispersion of alumina with improved mechanical properties such as hardness,Young’s modulus and yield strength by 40%,46%and 35%,respectively,when compared to that of pure Ni coating.Further,elasto-plastic indentation mechanics has shown that strength at 29%strain is enhanced to 110.5 GPa for 10 g/L Al2O3electrophoretically deposited Ni—yAI2O3 coating when compared to that of electrodeposited Ni（81.8 GPa）.     

Nanomechanical characterization of sputtered RuO2 thin film on silicon substrate for solid state electronic devices

This paper presents the study on characterizing the mechanical and interfacial properties of ruthenium dioxide (RuO₂) film on silicon substrate using nanoindentation tests. RuO₂ film is deposited by DC reactive magnetron sputtering; the structure and morphology of the film are characterized using X-ray diffraction and scanning electron microscopy, and elastic modulus and hardness are determined by nanoindentation with a standard Berkovich indenter and found to be 232.74 ± 22.03 GPa and 20.43 ± 2.37 GPa, respectively. In addition, the interfacial adhesion properties of RuO₂ film on Si substrate are studied. Spontaneous interfacial delamination is induced by indentations with wedge (90° and 120°) and conical indenter tips. The relationship between the indentation load-displacement (P-h) curves and the interfacial crack initiation and propagation are analyzed by combining FIB sectioning and SEM imaging. Through this analysis, the interface toughness of as-deposited RuO₂ film is found to be 0.046 ± 0.003 J/m² for 90° wedge indentation, 0.050 ± 0.004 J/m² for 120° wedge indentation, and 0.051 ± 0.003 J/m² for conical indentation.     

Low temperature chemical vapor deposition of nanocrystalline V2O5 thin films

Spatially uniform, carbon-free thin films of V₂O₅ were deposited on silicon by chemical vapor deposition using vanadium oxide triisopropoxide and water as gaseous precursors, in the temperature range of 100-300 °C. Films with substantial crystallinity were obtained for deposition temperatures as low as 180 °C. The “neat” chemistry that nominally leaves no fragments of ligand or water in the solid promotes film purity and reduces the deposition temperature needed for crystallization. Such deposition temperatures also open up additional possibilities for using crystalline vanadia on fragile substrates such as polymers for electronics and optical applications.     

A review of third generation SiC fibers and SiC_f/SiC composites

Compared with the first and second generations SiC fibers, the third generation SiC fibers have obvious improvement in heat-resistance, oxidation-resistance and creep-resistance, which promote the development of SiCf/SiC composite materials. Therefore, the third generation SiC fibers have more advantages and broader prospects in engineering applications. In this paper, the fabrication and properties of the third generation SiC fibers are compared and discussed. The preparation processes of the third generation SiC fibers reinforced SiC matrix composites and their application in aeroengine and nuclear energy fields are summarized, while their future development is prospected as well.     

FEA study on nanodeformation behaviors of amorphous silicon and borosilicate considering tip geometry for pit array fabrication

In order to predict the nanodeformation behaviors (piling-up, sinking-in, and elastic recovery) of hard-brittle materials such as amorphous silicon and Pyrex 7740 glass (borosilicate) indentation simulations were performed for various tip radii (40, 100, 200 nm), half-angle of conical indenter (55, 60, 65°), and indenter geometries (conical, Berkovich, spherical) by the numerical method with ABAQUS finite element software package. The result for conical indenter showed the smallest elastic recovery. The amorphous silicon showed higher pile-up than the Pyrex glass 7740 because it has a larger value of E/σ_y. It was also observed that the height of pile-up decreased with increasing amount of the elastic recovery. For a given indentation depth, the applied load and elastic recovery increased with a tip radius and half-angle due to the increase of the contact area. In addition, a larger plastic zone size formed with shaper indenter due to the higher stress concentration exerted.     

Trapping of water waves by moored bodies

Certain types of floating bodies are known to support trapped modes, with oscillatory fluid motion near the body and no energy radiation in the far field. Previous work has considered either fixed bodies, where the boundary conditions are homogeneous, or bodies which are freely floating and moving without any exciting force. For a fixed body the existence of a trapped mode implies that there is no unique solution of the boundary-value problem for the velocity potential with a prescribed body motion. For a free body which supports a trapped mode, the solution of the coupled problem for the motions of the fluid and body does not have a unique solution. A more general case is considered here, of a body with a linear restoring force such as an elastic mooring. The limiting cases of a fixed and free body correspond to infinite or zero values of the corresponding spring constant. A variety of body shapes are found including cylinders in two dimensions and axisymmetric bodies in three dimensions, which illustrate this more general case of trapping and provide a connection between the fixed and free cases.     

Dynamic nanoindentation testing for studying thermally activated processes from single to nanocrystalline metals

Nanoindentation experiments are widely used for assessing the local mechanical properties of materials. In recent years some new exciting developments have been performed for also analyzing thermally activated processes using indentation based techniques. This paper focuses on how thermally activated dislocation mechanisms can be assessed by indentation strain rate jump as well as creep testing. Therefore, a small overview is given on thermally activated dislocation mechanism and how indentation data from pointed indenters can be interpreted in terms of uniaxial macroscopic testing. This requires the use of the indentation strain rate as introduced by Lucas and Oliver as well as the concepts of Taylor hardening together with Johnson expanding cavity model.These concepts are then translated to nanoindentation strain rate jump tests as well as nanoindentation long term creep test, where the control of the indenter tip movement as well as the determination of the contact are quite important for reliable data. It is furthermore discussed, that for a steady state hardness test, the interpretation of the hardness data is straightforward and comparable to macroscopic testing. For other conditions where size effects play a major role, hardness data need to be interpreted with consideration for the microstructural length scale with respect to the contact radius.Finally strain rate jump testing and long term creep testings are used to assess different thermally activated mechanisms in single to nanocrystalline metals such as: Motion of dislocation kink pairs in bcc sx-W, Grain boundary processes in nc-Ni and ufg-Al, and the Portevin-le Chatelier effect in ufg-AA6014.     

An examination of trace surface on diamond-like carbon film after ball-on disk measurement

Hydrogenated diamond-like carbon (DLC) films were prepared by the radio frequency plasma-enhanced chemical vapor deposition method on silicon substrates using methane (CH₄) and hydrogen (H₂) gas. The wear track on DLC films was examined after the ball-on disk (BOD) measurement with a Raman mapping method. The BOD measurement of DLC films was performed for 1 to 3 h with a 1-hour step time. The sliding traces on the hydrogenated DLC film after the BOD measurement were also observed using an optical microscope. The films synthesized in this work had a very low friction coefficient (about 0.06) and were adhered very well without peeling off during the BOD measurement even with very thin thickness. Energy dispersive X-ray spectra show the decrease of C atomic % and the increase of O atomic % according to the sliding time. The novel Raman mapping method effectively showed the graphitization of DLC films according to the sliding time.     

Nanoindentation in more than one dimension – Experimental challenges and opportunities

The current status of nanoindentation apparatus and the requirements for extension to more than one dimension of loading is described. It is possible, though not trivial, to adequately characterise the stiffnesses and couplings present in a frictional contact and thus expand the present use of nanoindentation to important new areas. The example of static friction is discussed to show that complete machine characterisation is required if true interface mechanical properties and friction coefficients are to be correctly measured.