Finite element analyses were carried out to simulate the loading, unloading, and reloading processes of indentation tests. It was found that the validity of applying the elastic contact theory to the indentation unloading process is strongly related to the strain hardening and residual stress in impression. It is the combination of strain hardening and residual stress that causes the unloading or reloading curves to show elastic loading in the range from zero to the maximum load whereas the reloading curve on the impression without strain hardening and residual stress shows elastic–plastic loading in the same range. These computations indicate that applying the elastic contact theory to the unloading or reloading processes, the fundamental prerequisite of the instrumented indentation technique, is valid because of the existence of strain hardening and residual stress. The mechanism of this hardening effect is discussed through energy analysis.

GaP–GaAsP segmented nanowires (NWs), with diameters ranging between 20 and 500 nm and lengths between 0.5 and 2 μm, were catalytically grown from Au particles on a GaAs (111)B substrate in a gas source molecular beam epitaxy system. The morphology of the NWs was either pencil-shaped with a tapered tip or rod-shaped with a constant diameter along the entire length. Stacking faults were observed for most NWs with diameters greater than 30 nm, but thinner ones tended to exhibit fewer defects. Moreover, stacking faults were more likely found in GaAsP than in GaP. The composition of the pencil NWs exhibited a core–shell structure at the interface region, and rod-shaped NWs resulted in planar and atomically abrupt heterointerfaces. A detailed growth mechanism is presented based on a layer-by-layer growth mode for the rod-shaped NWs and a step-flow growth mode for the tapered region of the pencil NWs.

We present a structural feature of nacre in the red abalone shell: micrometer-scale screw dislocations in the aragonite layers and resultant growth via spiral motion. Compared to typical ionic or covalent crystals, nacre contains 106 screw dislocations per square centimeter, a difference of three orders of magnitude. Using electron microscopy, ion microscopy, and an in situ nano-manipulator, we studied the structure of screw dislocation cores in detail. We considered that these screw dislocations contribute significantly to the strengthening mechanisms that lead to nacre's extraordinary work of fracture, which is three orders of magnitude greater than that of aragonite and other monolithic crystals. This work suggests that the lamellar layers of aragonite propagate via a large number of continuous spiral growth domains as the “stacks of coins” become confluent. This model may provide a basis for creating new comparable micro/nanocomposites through synthetic or biomineralization means.

The structure and phase of the Al2O3 scale that forms on an Fe3Al-based alloy Fe-28Al-5Cr (at.%) was investigated by transmission electron microscopy and photoluminescence spectroscopy. Oxidation was performed at 900 °C and 1000 °C for up to 190 min. Transmission electron microscopy revealed that single-layer scales were formed after short oxidation times. Electron diffraction was used to show that the scales are composed of nanoscale crystallites of the θ, γ, and α phases of alumina. Band-like structure was observed extending along three 120°-separated directions within the surface plane. Textured θ and γ grains were the main components of the bands, whereas mixed α and transient phases were found between the bands. Extended oxidation produced a double-layered scale structure with a continuous α layer at the scale/alloy interface and a γ/θ layer at the gas surface. The mechanism for the formation of Al2O3 scales on iron aluminide alloys is discussed and compared with that for nickel aluminide alloys.

The changes in optical properties and damage mechanism of ZnO/silicone white paint caused by <200 keV protons in space were investigated in terms of ground-based simulation testing. The energies of protons were chosen as 50, 90, and 110 keV. The results show that the change in solar absorptance Δαs increases with increasing irradiation fluence as well as the proton energy. On the basis of photoluminescence spectroscopy, it is revealed that with increasing proton fluence, the 660-nm emission band related to the interstitial Zn-ions changes little, the 405-nm emission band related to the Zn vacancies decreases and tends to disappear, the 460-nm emission band related to the double ionized oxygen vacancies decreases, and the emission band related to the singly ionized oxygen vacancies increases. SRIM simulation analysis indicates that the damage effect of ZnO/silicone white paint caused by proton exposure would be aggravated due to the organic silicone binder. The proton irradiation leads to ionization of Zn atoms, formation of free oxygen and oxygen vacancies, and degradation of the organic silicone binder. It is believed that the optical degradation of ZnO/silicone white paint, induced by <200 keV protons, can be attributed to the combined effect of these three processes.

Well-organized mesoporous SiO2/TiO2 materials with crystallized framework were synthesized. The resultant materials showed high surface area (180–300 m2/g), narrow pore-size distribution (3.5–6 nm), and nanocrystalline framework. The influences of aging conditions on the mesoporous 80TiO2–20SiO2 materials were investigated. The water in the initial solution is beneficial for the mesostructural organization of the as-prepared sample while air moisture (relative humidity) during the aging process plays a key role in the crystallization of the calcined sample. Low aging temperature is another decisive factor to the formation of the mesostructure.

A multilayered structure of SiOx and SiOxCy on silicon substrate was prepared by plasma-enhanced chemical vapor deposition from gas mixtures of hexamethyldisiloxane and oxygen. Scanning transmission electron microscopy studies showed that the structure is well defined with distinct layers. The distributions of Si, C, and O were measured via electron energy-loss spectroscopy. We found that the elements C, Si, and O interdiffuse quite differently across the interfaces. The Si–L2,3 energy-loss near-edge structures in the SiOx and SiOxCy layers were different from those of pure Si, SiC, and Si3N4, which all contain a tetrahedral structure unit. Slight variations of the relative ratio of the first two sharp peaks at about 108 and 115 eV were found, which can probably be attributed to C partially substituting O atoms in the Si–O tetrahedral structure.

This paper presents an investigation on the corrosion behavior of five solders by means of polarization and electrochemical impedance spectroscopy (EIS) measurements. The Sn–9Zn and Sn–8Zn–3Bi solder, in comparison with the Sn–3.5Ag–0.5Cu and Sn–3.5Ag–0.5Cu–9In solder, were tested in 3.5 wt% NaCl solution and 0.1 wt% adipic acid solution, respectively. The Sn–37Pb solder was for reference in this work. The polarization curves indicated that the Sn–9Zn and Sn–8Zn–3Bi solder showed the worst corrosion resistance both in the salt and acid solutions, in terms of corrosion-current density, corrosion potential, linear polarization resistance, and passivation-current density. Meanwhile, the Sn–3.5Ag–0.5Cu solder remained the best corrosion characteristics in both solutions. It was found that due to microstructure alteration, Bi additive to the Sn–9Zn solder improved the corrosion behavior in the salt solution, whereas decreased that in the acid solution. However, the additive of In degraded the Sn–3.5Ag–0.5Cu solder in both solutions. The EIS results agreed well with the noble sequence of the five solders subjected to the two solutions with polarization. The equivalent circuits were also determined. Nevertheless, the four Pb-free solders exhibited acceptable corrosion properties since there was not much difference of key corrosion parameters between them and the Sn–37Pb solder.

Accurate mechanical characterization of viscoelastoplastic materials in small volumes is required for the development of polymeric thin film, nanocomposite, and biomedical applications. Instrumented indentation-based approaches are increasingly implemented to quantify the resistance to permanent deformation of such systems via time-independent analyses. Here, we quantify the significant post-indentation recovery of several bulk polymers via time-lapsed scanning-probe microscopy under ambient conditions, indicating up to 80% recovery of both indentation depth and volume within 48 h. This viscoelastic response demonstrates that indentation hardness values for these polymers are accurate within 10% for less than 5 min to 3.5 days post-indentation, neglecting any other analytical or experimental errors. Further, although the extent and rates of volumetric recovery depend strongly on loading history and polymer structure/physical properties, deformation resistance inferred from indentation hardness does not quantitatively or qualitatively predict recoverable work or residual deformation of polymer surfaces.

Melt-spun and annealed Al85Ni5Y8Co2 metallic glass, with a large supercooled liquid region, were investigated by means of differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and small-angle x-ray scattering (SAXS). TEM studies revealed that the as-quenched ribbons were fully amorphous. Further, the SAXS measurements showed that no evidence for compositional inhomogeneities associated with amorphous phase separation was found in the as-quenched state and the early stage annealing prior to devitrification. The primary crystallization of this glass was characterized, intriguingly, which appeared to be proceeded with an initial thermal relaxation, then α-Al nanocrystal nucleation with a limited number, finally a high density of nanocrystals nucleation and growth.

A nano-sized amorphous layer embedded in an atomic simulation cell was used to study the amorphous-to-crystalline (a-c) transition and subsequent phase transformation by molecular-dynamics computer simulations in 3C–SiC. The recovery of bond defects at the interfaces is an important process driving the initial epitaxial recrystallization of the amorphous layer, which is hindered by the nucleation of a polycrystalline 2H–SiC phase. The kink sites and triple junctions formed at the interfaces between 2H– and 3C–SiC provide low-energy paths for 2H–SiC atoms to transform to 3C–SiC atoms. The spectrum of activation energies associated with these processes ranges from below 0.8 eV to about 1.9 eV.

We report on the results of a comparative study in which the mechanical response of both fully dense and porous low-κ dielectric thin films was evaluated using two different techniques: nanoindentation and the plane-strain bulge test. Stiffness values measured by nanoindentation are systematically higher than those obtained using the bulge test technique. The difference between the measurements is caused by the Si substrate, which adds significantly to the contact stiffness in the indentation measurements. Depending on the properties of the coatings, the effect can be as large as 20%, even if the indentation depth is less than 5% of the film thickness. After correction of the nanoindentation results for the substrate effect using existing models, good agreement is achieved between both techniques. The results further show that densification of porous material under the indenter does not affect stiffness measurements significantly. By contrast, nanoindentation hardness values of porous thin films are affected by both substrate and densification effects. It is possible to eliminate the effect of densification and to extract the yield stress of the film using a model for the indentation of porous materials proposed by the authors. After correcting for substrate and densification effects, the nanoindentation results are in close agreement with the bulge test measurements. The results of this comparative study validate the numerical models proposed by Chen and Vlassak for the substrate effect and by Chen et al. for the densification effect.

A variety of carbon nano- and submicro-structures with spectacular morphologies such as spaghetti-like, dendritic, and segmented carbon fibers; carbon pillars; and single-walled carbon nanotubes (SWNTs) was selectively synthesized by the alcohol chemical vapor deposition (CVD) method. The phase structure and morphologies were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), and Raman spectroscopy. The carbon structures could be controlled by adjusting the deposition position and the growth temperature. The formation mechanism of these carbon structures was discussed on the basis of the experimental results. The various CVD products obviously imply that the growth mechanism for our alcohol CVD process evolves from catalytic growth mode to pyrolytic carbon deposition mode. The obtained various carbon nano- and submicro-structures may be promising for applications in functional nanodevices.

Nano-sized Bi2V0.9Cu0.1O5.35 powders were synthesized via a mechanochemical route from the component oxide mixture. However, a ball-milling duration of over 30 h was needed to ensure a high phase purity. Otherwise, the milled samples had poor sinterability and low sintered density since expansion occurred during sintering.

We report studies of the mechanical properties of tropocollagen molecules under different types of mechanical loading including tension, compression, shear, and bending. Our modeling yields predictions of the fracture strength of single tropocollagen molecules and polypeptides, and also allows for quantification of the interactions between tropocollagen molecules. Atomistic modeling predicts a persistence length of tropocollagen molecules ξ ≈ 23.4 nm, close to experimental measurements. Our studies suggest that to describe large-strain or hyperelastic properties, it is critical to include a correct description of the bond behavior and breaking processes at large bond stretch, information that stems from the quantum chemical details of bonding. We use full atomistic calculations to derive parameters for a mesoscopic bead-spring model of tropocollagen molecules. We demonstrate that the mesoscopic model enables one to study the finite temperature, long-time scale behavior of tropocollagen fibers, illustrating the dynamics of solvated tropocollagen molecules for different molecular lengths.

Nano- and micron-sized cellulose crystals were prepared and utilized as reinforcements for polyurethane composites. The cellulose crystals obtained from microcrystalline cellulose (MCC) were incorporated into a polar organic solvent, dimethylformamide (DMF), and ultrasonicated to obtain a stable suspension. The suspension was an effective means for incorporating the cellulose crystals into the polyol-isocyanate mixture, utilized to produce polyurethane composite films. The use of DMF presents an interesting alternative for the use of cellulose crystals as reinforcement of a broad new range of polymers. Moreover, the rheology of the uncured liquid suspensions was investigated, and analysis of the results indicated the formation of a filler structure pervading the liquid suspension. Besides, films were prepared by casting and thermal curing of the stable suspensions. Thermomechanical and mechanical testing of the films were carried out to analyze the performance of the composites. The results indicated that a strong filler-matrix interaction was developed during curing as a result of a chemical reaction occurring between the crystals and the isocyanate component.

Bulk fully nanocrystalline grain structures were successfully obtained in ultralow carbon stainless steel by means of equal channel angular pressing at room temperature. Transmission electron microscopy (TEM) and high-resolution TEM investigations indicated that two types of nanostructures were formed: nanocrystalline strain-induced martensite (body-centered cubic structure) with a mean grain size of 74 nm and nanocrystalline austenite (face-centered cubic structure) with a size of 31 nm characterized by dense deformation twins. The results about the formation of fully nanocrystalline grain structures in stainless steel suggested that a low stacking fault energy is exceptionally profitable for producing nanocrystalline materials by equal channel angular pressing.

A uniaxial tensile loading process was simulated on rectangular [001] oriented single-crystal Au, Ag, and Cu nanowires using the modified embedded atom method. The calculated theoretical tensile strength as well as elastic modulus and “yield strength” increases with decreasing wire width almost logarithmically, which is qualitatively consistent with relevant experimental results. According to the present observed linear relationship among these three parameters, we think, the size dependent mechanical behaviors in nanowires may be due to the enhanced attraction between atoms, which is caused by the accumulation of electron charges along wire axial direction.

Mg82Al8Ca10 was determined to be a pseudo-binary eutectic composition [liquid solidifying into α–Mg and (Mg,Al)2Ca in the Mg–Al–Ca ternary system with a eutectic melting temperature of 789 K]. A series of Mgx(Al0.44Ca0.56)100−x alloys, where 75 ≤ x ≤ 95, were cast into Φ4 mm rods using copper mold casting. The eutectic alloy exhibits the highest fracture strength, σf = 609 MPa. For 75 ≤ x ≥ 79, the alloys have hypereutectic microstructures with Mg2Ca as the primary phase, and σf is reduced together with diminishing plasticity. For hypoeutectic alloys with 86 ≤ x ≥ 95, the volume fraction of the primary α–Mg dendrites dispersed in the eutectic matrix increases with increasing x, resulting in a gradual decrease of the yield and fracture strengths but improved plastic strain to as large as 9%. The refined microstructures created in bulk samples via chill casting can lead to a good combination of strength and plasticity, with specific strength superior to commercial Mg alloys.

Interfacial reactions in γ–InSn4(Sn–20 at.% In)/Ni couples at 130, 140, 150, and 160 °C were investigated. Ni3Sn4 phase with significant indium solubility was formed in the couple reacted at 130 and 140 °C, and the reaction path was γ–InSn4/Ni3Sn4/Ni. For the couples reacted at 150 and 160 °C, even though both γ–InSn4 and Ni were solid phases, the liquid phase was formed in the couples. A distinguished feature was the nickel substrates becoming nonplanar with spikes at various locations and the Ni3Sn4 phase layer on top of the nickel spikes. Except at regions near the nickel spikes, the reaction layer consisted of precipitates and was not a homogeneous phase. The reaction path is γ–InSn4/Ni3Sn4/Ni at the location with Ni3Sn4 phase growing on Ni. However, if the Ni3Sn4 phase does not nucleate, the liquid phase forms at the interface with accumulation of indium atoms, and the reaction path is γ–InSn4/ liquid/liquid + Ni3Sn4/Ni.