Experiments have shown that nanoindentation unloading curves obtained with Berkovich triangular pyramidal indenters are usually welldescribed by the power-law relation P = α(h − hf)m, where hf is the final depth after complete unloading and α and m are material constants. However, the power-law exponent is not fixed at an integral value, as would be the case for elastic contact by a conical indenter (m = 2) or a flat circular punch (m = 1), but varies from material to material in the range m = 1.2–1.6. A simple model is developed based on observations from finite element simulations of indentation of elastic–plastic materials by a rigid cone that provides a physical explanation for the behavior. The model, which is based on the concept of an indenter with an “effective shape” whose geometry is determined by the shape of the plastic hardness impression formed during indentation, provides a means by which the material constants in the power law relation can be related to more fundamental material properties such as the elastic modulus and hardness. Simple arguments are presented from which the effective indenter shape can be derived from the pressure distribution under the indenter.

A micromachined specimen with a test section only 150-μm thick was developed for investigating subcritical crack growth in silicon. Crack growth rates in the range 10−4–10−10 m/s were measured as a function of applied stress intensity (v–K curves) during tests in humid air and dry nitrogen lasting up to 24 h. The fracture toughness, KIc of {110} silicon was also measured at 1.15 ± 0.08 MPa m1/2. While some evidence MPa-m1/2 of subcritical crack growth appeared to occur in the region 0.9 KIc < K > 0.98 KIc, the extremely high crack growth exponent (n 100) and the high ratio of the apparent stress corrosion threshold, KIscc, to the fracture toughness, KIscc/KIc > 0.9, suggests that no clear evidence exists for a stress corrosion process in silicon exposed to humid air.

Sintering studies on Y–Ba–Cu oxide (YBCO)–Agx (x = 0, 0.6, and 1.0 mol) powder were carried out in argon atmosphere to understand the role of silver addition on the densification behavior of these materials. The increase of sintered densities of the compacts with silver addition in argon atmosphere contradicted our earlier observation on sintering of YBCO–Agx powder compacts in air, where the densities decreased for x > 0.6. Thermogravimetric (TG) studies under argon atmosphere indicate a continuous decrease of mass on heating suggesting an enhanced rate of oxygen removal from the YBCO matrix that facilitated the sintering in argon atmosphere. Sintering studies of YBCO–Agx powder compacts in argon in conjunction with earlier observations in air has substantiated our claim that high-temperature oxygen desorption by the silver from the YBCO matrix to the sintering atmosphere controls the rate of densification for these superconducting composites. However, the apparent activation energies for sintering suggest that the sintering process is controlled by yttrium ion diffusion along bulk and grain boundaries.

Polydimethylsiloxane (PDMS) films were prepared on silicon wafers by spin coating. The tribological properties of the PDMS films sliding against AISI-52100 steel ball were investigated with a dynamic static friction coefficient measurement apparatus in a ball-on-plate configuration. It was found that crosslinking, end grafting, and chemical characteristics of the substrate surfaces combined to play an important role in keeping the films' stability and improving the friction-reduction and wear-resistant properties. It was also noted that crosslinked PDMS films on hydroxylated substrates exhibited the most stable friction coefficient and the longest antiwear life, while a friction coefficient below 0.01 was observed for the crosslinked PDMS films on hydrophobic substrates. The latter might be attributed to the weak interaction at the interface of PDMS layer and the self-assembled monolayer. The friction coefficient appeared to be velocity dependent. At higher sliding velocities, the films showed more stable and smaller friction coefficients; this might be attributed to the shear thinning effect.

Cu47Ti34Zr11Ni8 amorphous gas atomized powders were consolidated by warm extrusion. After consolidation near 723 K using an extrusion ratio of 5, the material retains between 88% and 98% of the amorphous structure found in the gas atomized powder. The onsets of the glass transition and crystallization temperatures of this extruded material are observed respectively at slightly higher and lower temperatures than those of the starting powders. These temperature shifts are attributed to a composition change in the remaining amorphous phase during partial devitrification throughout the extrusion process. Powders extruded at the same temperature, but using higher extrusion ratios of 9 and 13, exhibit substantial devitrification during the consolidation process yet still deform homogeneously.

The effect of electropulsing on the evolution of an elliptical cylinder microcrack was studied from a thermodynamic point of view. An analytical expression for the healing driving force with respect to the passing electric current density, crack geometric shape, Young's modulus, and sample size was derived. The critical current density for crack healing was calculated and agreed with the experimental results very well. The heterogeneous temperature rise due to Joule heat was calculated and proved ideal to the crack healing. Earlier experimental results can be fully understood within the present theoretical frame.

A high-energy ball milling procedure has been developed to produce amorphous alloys in Ti50(Cu0.45Ni0.55)44−xAlxSi4B2 (x= 0, 4, 8, 12) powder mixtures. The milling products were characterized using x-ray diffraction, differential scanning calorimetry, and transmission electron microscopy. The Ti-based amorphous alloy powders prepared through this solid-state process exhibit a well-defined glass transition and a supercooled liquid region (ΔTx =64 K) close to the largest achieved so far for Ti-based undercooled melts. The substitution of Al for Cu and Ni has beneficial effects on stabilizing the supercooled liquid. Residual nanocrystals of the αTi structure are uniformly dispersed in the amorphous matrix. The composite alloy powders offer the potential for consolidation in the supercooled liquid region to bulk lightweight amorphous alloys and the possibility to attain desirable mechanical properties.

The effect of Zn doping on crystallization of gallophosphate molecular sieve, cloverite, synthesized hydrothermally at 170 °C, using starting gels with ZnO, was investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM), and molecular dynamics (MD) simulation, etc. The SEM observations and crystallinities estimated from XRD data revealed that Zn-doped cloverite with very good crystallinity was successfully prepared, and the addition of ZnO to the starting gel was effective in promoting the crystallization process in a short reaction time. The results of chemical analyses, estimated unit cell dimensions, and MD simulations suggested the substitution of Zn atoms for Ga atoms in the framework of Zn-doped cloverite.

Nanocomposite powders of Ni–Al2O3 (5 and 10 vol% Ni) were prepared from porous alumina preforms with high specific area (100 m2 g?1) impregnated with nickel nitrate. Samples were obtained by reduction under a controlled oxygen partial pressure either directly or through an intermediate step, giving nickel aluminum spinel. In both cases, homogeneous dispersions of nickel particles in the alumina matrix were achieved. The Ni particle size ranged from 10 to 100 nm, depending on the preparation conditions and temperature.

The effect of Ni substitution on the structure and photocatalytic H2 and O2 evolutions of InTaO4 under visible light irradiation (λ > 420 nm) from aqueous CH3OH/H2O and AgNO3/H2O solutions were investigated. The photocatalysts were prepared by the solid-state reaction method and characterized by powder x-ray diffraction and Rietveld structure refinement. These photocatalysts crystallize in the same wolframite structure, but lattice parameters decrease with increase of x in In1−xNixTaO4 (0 ≤x ≤ 0.2). The photocatalytic activity changed with the variation of x in In1−xNixTaO4and the photocatalyst at x = 0.1 showed the highest activity, which increased 8 times compared with nonsubstituted photocatalyst.

Residual stress in a thin film was analyzed by the nanoindentation technique. Two dominant effects of residual stress to indentation were summarized as the slope change in loading curve and the invariant value of intrinsic hardness. A stress-sensitive reversibly deformed zone around contact was modeled to explain the indentation behaviors under a residually stressed state. Finally, the residual stress was evaluated from the changes in contact shape and applied load during stress relaxation under the condition of constant indentation depth. The residual stresses in diamond-like carbon and Au films analyzed from this model agreed well with the average values measured by the curvature method.

Polycrystalline samples of Ca1-xBixMnO3 (0.02 ≤ x ≤ 0.20) were studied by means of x-ray diffraction, electrical resistivity (ρ), thermoelectric power (S), and thermal conductivity (κ) at high temperature. Bi doping leads to the lattice parameters a, b, and c increasing. And the ρ and the absolute value of S decrease rapidly with Bi doping. The largest power factor, S2/ρ, is obtained in the x = 0.04 sample, which is 3.6×10−4 Wm−1 K−2 at 400 K. The figures of merit (Z = S2/ρκ) for this sample and 1.0×10−4 and 0.86 × 10−4 K−1 at 600 and 1000 K, respectively.

Zr70Ni23Ti7 alloy contains a single amorphous phase when it is melt-spun at a wheel surface velocity over 20 m/s. The crystallization of these amorphous ribbons takes place through two exothermic reactions and shows a significant supercooled liquid region of about 30 K, indicating that the Zr70Ni23Ti7 alloy has a good glass-forming ability. The crystallization products of the first exothermic reaction for the ribbon prepared at a wheel surface velocity of 40 m/s are mainly an icosahedral quasicrystalline phase (I-phase) and some Zr2Ni phases. Further heating to a higher temperature will lead to the transformation of the metastable I-phase to Zr2Ni. Some icosahedral atomic clusters with a structure similar to those in face-centered-cubic Zr2Ni may exist in the alloy after rapid quenching, and most of them may act as nuclei of I-phase. The formation of I-phase in this alloy without any noble metals may be due to the proper atomic ratios in the system.

The solution-precursor plasma spray (SPPS) method is a new process for depositing thick ceramic coatings, where solution feedstock (liquid) is injected into a plasma. This versatile method has several advantages over the conventional plasma spray method, and it can be used to deposit nanostructured, porous coatings of a wide variety of oxide and non-oxide ceramics for a myriad of possible applications. In an effort to understand the SPPS deposition process, key diagnostic and characterization experiments were performed on SPPS coatings in the Y2O3-stabilized ZrO2 (YSZ) system. The results from these experiments show that there are multiple pathways to SPPS coating formation. The atomized precursor droplets undergo rapid evaporation and breakup in the plasma. This is followed by precipitation, gelation, pyrolysis, and sintering. The different types of particles reach the substrate and are bonded to the substrate or the coating by sintering in the heat of the plasma. The precursor also reaches the substrate or the coating. This precursor pyrolyzes in situ on the substrate, either after it reaches a “cold” substrate or upon contact on a “hot” substrate and helps bond the particles. The coating microstructure evolves during SPPS deposition as the coating temperature reaches approximately 770 °C.

Metal contact of compound semiconductors has been extensively studied using various characterization tools. However, there was little work of scanning transmission electron microscopy (STEM) done previously for the study of the InP contact systems. Using STEM and Auger electron spectroscopy analyses, we correlated the resistance with interfacial reactions in the AuGe/Ni/Au/Cr/Au contacts to n-InP. Detailed nanoscale structural and chemical information was uniquely revealed by the STEM compared to other techniques. For the high-resistance samples, little interfacial reaction between n-InP and Au occurred. For the low-resistance samples, significant out-diffusion of P in the Au and Ni layers occurred, forming Au–P and Ni–P metallic compounds. Accumulation of Ge in the Ni layer was also detected. We suggest that Ni–P may be very critical in obtaining low contact resistance for n-InP.

This paper summarizes the effects of selected processing parameters on the behavior of aqueous alumina suspensions during hydrolysis-assisted solidification and on the properties of the green and sintered parts prepared by this technique. Measurements of the changes in viscosity, the pH, and the impedance of aqueous suspensions with time were performed to evaluate the process. Using impedance spectroscopy, the effects of the addition of AlN, the solids content in the ceramic suspension, and the effect of the solidification temperature on the progress of solidification were followed. It was demonstrated that the solidification temperature significantly affects not only the solidification rate but also the properties of the green and sintered parts. A transmission electron microscopy analysis of dry green parts revealed that the host ceramic particles are bound by a predominantly amorphous AlOOH phase, which results in a high strength for the green parts.

Sm2+ ion-doped Al2O3–SiO2 glasses were prepared using sol-gel and melt-quenching methods; the redox equilibrium and spectral hole burning were investigated. The Sm3+ ions were reduced into Sm2+ by heating in H2 gas or x-ray irradiation. The redox between the Sm3+ and Sm2+ obeyed first-order kinetics, the rate of which was larger for the sol-gel glasses. The Sm3+ ions were also reduced by x-ray irradiation and the activation energy for redox equilibrium was half of that for the glasses treated in H2 gas. Two different mechanisms were proposed for the redox reaction of the samarium ions. In the x-ray irradiated glasses, the Sm3+ ions were reduced into Sm2+ by electron transfer from the oxygen defect center, whereas the H2-gas reaction removed the oxygen ions to reduce the Sm3+ ions. The spectral hole burning of the x-ray-irradiated glasses could be burned by the reverse reaction of the reduction of the Sm3+ ions; that is, the electron transfer from the excited Sm2+ into the surrounding oxygen. A short distance between the Sm2+ and oxygen defect centers allowed fast hole burning. On the other hand, the hole burning in the H2-treated glasses was performed by electron transfer between Sm2+ and another trapping center such as Sm3+.

Comparative investigations are carried out for spectral (Raman) electrical and structural properties of V2O5 single crystals and polycrystalline samples obtained by IR laser light illumination of pure metallic samples in an oxidizing atmosphere (air). It is shown that the structures grown on metallic plates in the field of laser light are predominantly V2O5 polycrystals. Raman measurements reveal that the main peaks, which are characteristic for single crystals, are also present in laser-driven samples but with different intensities. Some peaks are attributed to laser-grown thick films, which are not present in the single-crystalline phase. There are shifts in the peak positions indicating the existence of different force constants for films as compared with crystals. The activation energies obtained from the electrical properties (conductivity, impedance versus temperature) yield similar values except for the anisotropic characteristics of the single crystal where the values are a bit different along different crystallographic axes (unlike the polycrystalline oxide films made by the laser). The single-crystalline phase has a well-defined layered structure with well-defined shapes showing formed units of truncated oktaeders, while the film structure shows randomly distributed tubular micron-size structures with empty holes at the peripheral part of the irradiated area, and nanoscaled long and thin tubes well oriented along the direction of the incoming laser light in the central part of the irradiation spot.

A macroscopic-scale depth-sensing indentation apparatus with the ability to be mounted on an inverted microscope for in situ observation of contact events was calibrated using the Oliver and Pharr [J. Mater. Res. 7, 1564 (1992)] procedure with a two-parameter area function. The calibrated Vickers tip was used to determine the projected contact area at peak load and the modulus and hardness of a variety of non-metallic materials through deconvolution of the measured load-displacement traces. The predicted contact area was found to be identical to the measured area of residual contact impressions. Furthermore, for transparent ceramic materials the projected contact area during loading was found to be the same as the area measured from the diagonal of post-indentation residual contact impressions. The modulus and hardness values deconvoluted from the load–displacement traces were compared with independent measurements. The effects of sample clamping, column compliance, and tip radius on the load–displacement data and inferred materials properties were also examined. It is suggested that the simplicity of instrumentation and operation, combined with the ability to observe indentations optically, even in situ, makes macroscopic-scale depth-sensing indentation ideal for fundamental studies of contact mechanics.

We investigated the dependence of critical current density (Jc) on thickness of Yba2Cu3O7−δ (YBCO) films grown by pulsed laser deposition on (100) SrTiO3 (STO) and on rolling-assisted biaxially textured substrates (RABiTS). The thickness of YBCO films varied from 0.19 to 3 μm. The highest Jcs of 5.3 and 2.6 MA/cm2 at 77 K, self-field were obtained for 0.19-μm YBCO films on STO and RABiTS, respectively. Jc was found to decrease exponentially with YBCO thickness on both substrates. However, the results suggest different mechanisms are responsible for the Jc reduction in the two cases. On STO, growth of a-axis grains within c-axis films and broadening of the in-plane texture were observed in thick films. On RABiTS, degradation in cube texture as well as development of a porous surface morphology were found to correlate with film thickness.