A new experimental technique is presented for making measurements of biaxial residual stress using load and depth sensing indentation (nanoindentation). The technique is based on spherical indentation, which, in certain deformation regimes, can be much more sensitive to residual stress than indentation with sharp pyramidal indenters like the Berkovich. Two different methods of analysis were developed: one requiring an independent measure of the material's yield strength and the other a reference specimen in the unstressed state or other known reference condition. Experiments conducted on aluminum alloys to which controlled biaxial bending stresses were applied showed that the methods are capable of measuring the residual stress to within 10–20% of the specimen yield stress. Because the methods do not require imaging of the hardness impressions, they are potentially useful for making localized measurements of residual stress, as in thin films or small volumes, or for characterization of point-to-point spatial variations of the surface stress.

Barium titanate nanosized powders were prepared by a slightly modified Pechini method. The obtained polymerized resin was used as the precursor for BaTiO3 powder production. DTA TG thermal analysis indicated that thermal decomposition of the precursors proceeds through four major step processes: (i) dehydration reaction; (ii) combustion reactions; (iii) intermediate phases formation; (iv) decarbonation of the intermediate to give BaTiO3. X-ray diffractometry (XRD) and Raman spectroscopy results indicated that, depending on the heating rate, the BaTiO3 formation took place via a predominant solid-state reaction between nanosized BaCO3 and amorphous TiO2 (TiO2−x) when crystallized by a low-heating rate (1.5 °C/min), although a small amount of a quasi-amorphous intermediate phase was also present. BaTiO3 crystallization by rapid heating rate (5 °C/min) took place through a quasi-amorphous intermediate phase formation as the main rate-controlling factor for the crystallization process. The fact that the low heating rate minimizes the intermediate phase content indicates the strong influence of the thermal heating on the kinetics of the involved transformation or in the mechanism. Although XRD results seem to indicate the formation of pseudocubic BaTiO3 as the final reaction product, the Raman spectra indicated as more probable the formation of a mixture of an oxygen-deficient hexagonal and tetragonal BaTiO3 phases below 700 °C. Above that temperature the tetragonal BaTiO3 was the only phase present. As-prepared BaTiO3 strongly agglomerated powders were relatively sinter active, leading to dense ceramic bodies (≥95% of the theoretical value). Microstructural (grain size approximately 1 mm) and room-temperature dielectric properties (ετ ≈ 2000 and tan δ ≤ 2%) at 10 kHz indicated that the obtained powders have to be optimized.

Cathodoluminescence emission spectra and photoluminescence (PL) excitation spectra were used to evaluate Eu+3 and Cr+3 as activators for red luminescence in ZnGa2O4. In the ZnGa2O4:Eu materials red emission from Eu+3 and blue intrinsic emission were observed. The blue intrinsic emission increased relative the Eu+3 emission with increasing current density and is attributed to preferential current saturation of the Eu+3 activators. In addition, PL excitation measurements revealed that the inefficient energy transfer from the ZnGa2O4 host to the Eu+3 is due to poor spectral overlap between the ZnGa2O4 emission and the Eu+3 absorption. Cr-doping resulted in a saturated red-color, and no host emission was observed over the entire current density regime investigated. The PL excitation of the ZnGa2O4:Cr revealed good overlap between the ZnGa2O4 host and the Cr+3 absorption. Efficient energy transfer to the Cr+3 activators occurs via multipolar interactions.

Microstructures of La1-xCaxMnO3 compounds (x = ⅓ and 0.5) prepared with and without intermediate grinding were studied using transmission electron microscopy. A high density of antiphase boundaries (APBs) with displacement vector 1/2 〈111〉, indexed in orthorhombic unit cell, has been observed in bulk samples with no or minimum intermediate grinding. The nature of this APB is analyzed and found to bedue to the symmetry breaking introduced by the tilting of MnO6 octahedra relative to the ideal perovskite structure. Samples prepared using two intermediate grinds do not show these defects indicating that the microstructure can be controlled through synthesis routes. The effect of domain boundaries on the colossal magnetoresistance effect is discussed.

Complete control of the texture of a film during growth requires the ability to determine the in-plane and out-of-plane texture simultaneously. We present both computer simulation and experimental evidence for the simultaneous establishment of out-of-plane and in-plane texture during ion beam assisted deposition of aluminum. Channeling along 〈110〉 directions (60° from the normal) creates a {220} out-of-plane orientation rather than the thermodynamically preferred {111} orientation. The ion beam also aligned 〈220〉 directions within the plane of the film. Measured x-ray pole figures confirmed the presence of a strong out-of-plane texture and the presence of two main, twin-related, in-plane texture components. We theoretically demonstrated that it is impossible to completely control both the in-plane and out-of-plane texture with a single ion beam in high-symmetry crystals and two ion beams must be employed to ensure complete texture control.

Barium-strontium titanate (BST) thin films were prepared by a two-step deposition using radio-frequency magnetron sputtering on Pt/Ti/SiO2-buffered Si(100) substrate. The initial BST layer thickness and intermediate annealing strongly affect the resultant electric properties of the two-step BST thin films. The optimal two-step BST films, with a first-layer thickness of 30 nm intermediate annealed at 610 °C under 1 torr oxygen. The dielectric breakdown and leakage current density of the two-step film are above 625 kV/cm and 9.5 nA/cm2 at 100 kV/cm, respectively, compared with 400 kV/cm and 17 nA/cm2 for the one-step films. We conclude that the two-step deposition dramatically improves dielectric breakdown and enhances leakage current density while keeping the dielectric constant uninfluenced.

The effects of strain hardenability and strain rate sensitivity on the plastic flow and deformation inhomogeneity during equal channel angular pressing were studied using a finite element method analysis. In this study, perfect plastic nonhardening and rate-insensitive materials, and rate-sensitive materials were considered. In case of the nonhardening and rate-insensitive materials, the deformed geometry was predicted to be quite uniform and homogeneous. Deformation inhomogeneity developed, however, in materials with finite work-hardening exponent and strain-rate sensitivity. The corner gap formed in strain-hardening materials whereas the upper and lower channel gaps formed in strain-rate-sensitive materials. The deformation inhomogeneity was strongly dependent on the relative effects of strain-hardening exponent and strain-rate sensitivity. The predictions on the deformation inhomogeneity and the formation of corner and channel gaps were compatible with the experimental data published in the literature.

The present study of rapidly solidified melt-spun Al80Fe14Si6 Al80V14Si6, and Al80Fe10V4Si6 alloys by electron microscopy techniques, x-ray diffractometry, and differential scanning calorimetry leads to a number of microstructural results. Coexistence of a micro-quasicrystalline state of an icosahedral phase with monoclinic θ–Al13Fe4 and hexagonal β–Al6V in Al–Fe–Si and Al–V–Si alloys, respectively, is reported. Also, the growth morphology of the icosahedral phase surrounded by a crystalline ring was investigated in an Al–Fe–V–Si alloy. The crystalline ring has the particles of the cubic α–Al12(Fe,V)3Si silicide phase. Evidence of irrational twinning of cubic crystals, giving rise to a symmetry not deviating much from icosahedral symmetry was found in this alloy. In all the three alloys crystalline intermetallics were elucidated in the context of rational approximants of an icosahedral quasicrystal. It was noticed that while the icosahedral phase in Al–Fe–Si and Al–V–Si alloys transforms to crystalline intermetallics at about the same temperature (approximately 610 K), the transformation of icosahedral phase in Al–Fe–V–Si alloy occurred at a relatively lower temperature (540 K). The origin of different metastable microstructures and their stability at elevated temperatures, in these alloys, are compared and discussed.

Hydroxyapatite (HA) coatings with different thicknesses were produced on Ti and Si substrates using the radio frequency magnetron sputtering method. The mechanical properties, for example, modulus and hardness, of the coatings were measured using nanoindentation. The measured values of modulus and hardness were close to the upper limit of that reported for bulk HA, indicating a fully dense structure. Interfacial strengths between the HA coatings and substrates were also evaluated using a nanoscratch technique. The HA–Ti interface appeared to be stronger than the HA–Si interface. The microstructures of the HA coating and the HA–Ti interface were examined using high-resolution electron microscopy. Chemical compositions of the HA coating and the HA–Ti interface were also analyzed using x-ray energy dispersive spectrometer and electron energy loss spectroscopy. The results indicated that the strong HA–Ti bonding is associated with an outward diffusion of Ti into HA layer and concomitant formation of TiO2 at or near the interface.

The FexZn1−xF2 alloy has been shown to be a model system for studying the magnetic phase diagram of dilute magnets. Whereas the growth of bulk single crystals with fixed Zn concentrations is difficult, the thin film growth is comparatively simpler and more flexible. To gain an understanding of the growth of FexZn1−xF2 films, a method was developed to grow smooth films at fixed concentrations. This was done by depositing a MgF2 buffer layer on MgF2(001) substrates and then depositing FeF2 and ZnF2 [001]-orientated epitaxial thin films at different temperatures. Surprisingly, the lattice spacing depends strongly on the growth temperature, for 44-nm-thick FeF2 films and 77-nm-thick ZnF2 films. This indicates a significant amount of stress, despite the close lattice match between the films and the MgF2 substrate. Thick alloy samples (approximately 500 nm thick) were grown by co-evaporation from the FeF2 and ZnF2 sources at the ideal temperature determined from the growth study, and their concentration was accurately determined using x-ray diffraction.

A precursor solution for processing lithium niobate (LiNbO3) films was prepared from lithium niobium ethoxides through modification with acetic acid in hydrolysis. Homogeneous gel films were spin-coated on various substrates. Highly oriented LiNbO3 films were crystallized on sapphire and Pt-coated substrates by heat treatment at 500 °C. Crystallization behavior of the LiNbO3 films depended on the orientation of platinum under-layer films. LiNbO3 films crystallized with preferred (001) orientation on Pt(111) layers, while LiNbO3 films crystallized with preferred (113) orientation on Pt(100) layers. LiNbO3 films prepared on Si(111), SiO2, and MgO(100) substrates showed polycrystalline characteristics with less orientation by heat treatment at 500 °C.

Continuous high-quality fibers of yttria-doped zirconia with 4 and 8 mol% yttria were blow spun using an inorganic sol precursor. The fibers were heated and analyzed using scanning electron microscopy, x-ray diffraction, differential thermal/thermogravimetric analysis, and surface area/porosity by nitrogen adsorption. The fibers were of a single-phase cubic structure after crystallization at 529 °C and typically 3.3–5.5 or 7.5–11.5 μm in diameter depending on the composition. Samples of fibers were heated to various temperatures and their friability index and creep properties analyzed using the bend stress relaxation technique and compared to other fibers of similar composition prepared by different solution techniques and commercially available fibers.

Microscale sensing and actuating components are prevalent in microelectromechanical systems. Deformations of microscale components are dependent not only on the strains in the body, but also on the strain gradients. The contribution of strain gradients to plastic hardening is characterized by the specific strain gradient modulus of the material. The specific strain gradient modulus has been predicted to vary with the plastic strain. The moduli of plastically prestrained epoxy specimens were experimentally characterized in this investigation using nanoindentation. Prestraining induced softening and an energy model are developed to separate the effect of prestrain softening from the effect of strain gradient. The results indicated that the contribution of strain gradient to hardening was initially large but diminished with increased plastic deformation. A model was developed for power law material and was shown to compare well with the experimental results.

The crystallization process of SrxBiyTa2O5+x+3y/2 thin films grown by metalorganic chemical vapor deposition was investigated. Phase formation and crystal growth is greatly affected by the film composition and crystallization temperature. Phase diagrams for varying Sr or Bi contents were determined as a function of the crystallization temperature. The higher the Sr or Bi content in the film, the lower the phase transition temperature from the amorphous to the fluorite-type phase and from the fluorite-type to the Bi-layered Aurivillius phase. Low Sr and Bi contents support pyrochlore-type phase formation as a second phase. During annealing, excess Bi is not lost due to evaporation, but due to migration to the bottom electrode. Contrary to the fluorite-type phase, the Aurivillius phase is not able to incorporate the excess of Bi atoms. Decreasing grain size and pyrochlore-type phase formation entail decreasing remanent polarization.

The fretting wear of sulphur-deficient MoSx coatings with different crystallographic orientations has been investigated in ambient air of controlled relative humidity. The coefficient of friction and the wear rate of MoSx coatings sliding against corundum depend not only on fretting parameters like contact stress, fretting frequency, and relative humidity, but also strongly on the crystallographic orientation of the coatings. For randomly oriented MoSx coatings, the coefficient of friction and the wear rate increased significantly with increasing relative humidity. In contrast, basal-oriented MoSx coatings were less sensitive to relative humidity. The coefficient of friction of both types of MoSx coatings decreased on sliding against corundum with increasing contact stress and decreasing fretting frequency. A correlation between dissipated energy and wear volume is proposed. This approach allows detection in a simple way of differences in fretting wear resistance between random- and basal-oriented MoSx coatings tested in ambient air of different relative humidity.

Recently, it was demonstrated that Ni99.45B0.55 undergoes grain refinement by either remelting or dynamic nucleation at two different undercoolings. In this work, we found that the grain refinement by remelting can be characterized by a gradual disappearance of the texture of the initially formed dendrites in the transition regime while the grain refinement by dynamic nucleation is characterized by a sudden disappearance of texture.

During thermal cycling through the α–β phase transformation under the action of a small external biasing stress, Ti alloys exhibit an average deformation stress exponent of unity and achieve superplastic strains. We report tensile experiments on Ti–6Al–4V with an applied stress of 4.5 MPa, aimed at understanding the failure processes during transformation superplasticity. The development of cavities was assessed as a function of superplastic elongation, and macroscopic neck formation was quantified at several levels of elongation by digital imaging techniques. The effects of thermal inhomogeneity on neck initiation and propagation were also elucidated experimentally. Tensile ductility during transformation superplasticity is compared with that during isothermal creep at the average, effective cycling temperature, and a numerical model is used to show the effect of thermal gradients in limiting superplastic elongation.

Depth-sensing indentation tests can be used to estimate the Young's modulus, hardness, and other characteristics of material behavior. For many materials, the unloading segment of the load–depth curve contains only elastic recovery while the loading segment can contain elastic and plastic deformation. In this paper a new method is presented to determine the Young's modulus of a material from the loading segment of an indentation test. A depth-sensitive hardness tester was used with a load cell integrated into the closed-loop system. Defined mechanical oscillations with constant frequency were generated by adding a piezoelectric stack to the closed loop of the hardness measurement system. Thus the resonance response of the system was obtained, which includes information regarding the stiffness of the tested material. This new method was tested on two polymers and two glasses, an optical and a conventional one. The results obtained for the Young's modulus were in good agreement with other accepted methods.

Like many other oxides, MnZn ferrite shows a considerably decreased strength in a humid environment. Conventionally one explains this behavior by subcritical crack growth, i.e., a kinetic effect affecting the oxygen–metal bond breaking rate at the crack tip via a reaction with water. The dissociation of water in a proton and hydroxyl ion is considered as crucial. However, it appears that also other gases have a detrimental effect on the strength. In this paper the effect of H2O, H2S, NH3, NO, and CO on the strength of MnZn ferrite have been studied experimentally. For water a clear minimum in strength occurs at relative low partial pressure. For the other gases the data also indicate a minimum. An adsorption model taking into account the presence of competitive adsorption mechanisms, involving dissociative and nondissociative adsorption of the adsorbate and the (non)dissociative adsorption of the ever present N2, is presented. This model can explain the experimentally observed features well. Although kinetic effects induce subcritical crack growth in MnZn ferrites, it is concluded that adsorption is an important strength lowering effect for MnZn ferrite when exposed to active gases.

Crystalline and pore-free films of α–Fe2O3 were prepared on hydrophilic self-assembled organic monolayers (DTT-SAMs) at 80 °C. Subsequently, Fe3O4 and γ–Fe2O3 films were synthesized via post annealing of as-deposited α–Fe2O3. In situ patterning of crystalline iron oxide thin layers was achieved via microcontact printing (μCP) and selective deposition. μCP was used to pattern two different surface moieties of self-assembled organic monolayers (SAMs) on Au–Cr–Si substrates. An elastomeric stamp was used to transfer either hexadecanethiol (HDT) SAMs, which are to sustain deposition of iron oxide precipitates, or hydrophilic SAMs [e.g., dithiothreitol (DTT)]. Selective deposition was realized through precipitation of iron oxide phases. Iron oxide films were deposited onto hydrophilic SAMs, but not onto HDT surfaces. Line (width of <1 μm) patterns in crystalline α–Fe2O3 thin films were obtained.