We succeeded in fabricating c-axis (00l) oriented ZnO ceramics by using a rotating magnetic field and a subsequent sintering treatment. The degree of orientation in the green compact was about 0.5 along (00l) on the Lotgering scale. The degree of orientation increased to 0.99 after sintering at 1573 K. Particles can also be oriented in a static magnetic field, but along the direction of the a-axis or a,b-axes (h00), (hk0). These results show that selected axes can be oriented by controlling the magnetic field. Control of the crystal form in microstructures is expected to result in improvements in and better miniaturization of functional ceramics.

The elastic modulus of an amorphous polymer was investigated by nanoindentation using combinations of ten total penetration depths and three constant unload rates. This experimental design provided a range of unloading strain rates coexisting with a range of depths. The elastic modulus of the material was found to correlate strongly with the unloading strain rate, whereas its correlation with the indentation depth was statistically nonsignificant. Thus, the increase of elastic modulus that occurred with decreasing depth at each constant unload rate was merely due to the increasing unloading strain rate associated with the decreasing depth. The true depth dependence of a rate-dependent material can therefore be studied only by maintaining a constant unloading strain rate across the entire depth range. The implications of these results to the continuous stiffness measurement technique are considered.

A new technique for measuring the elastic-plastic properties of porous thin films by means of nanoindentation is proposed. The effects of porosity on indentation hardness and modulus are investigated through finite element analyses based on the Gurson model for plastic deformation of ductile porous materials. Intrinsic mechanical properties of the thin film are obtained by eliminating both substrate and densification effects. The technique is applied to the special case of a porous, low-permittivity dielectric thin film. The results are in good agreement with those obtained independently using the plane-strain bulge test.

Technical issues surrounding the use of nanoindentation at elevated temperatures are discussed, including heat management, thermal equilibration, instrumental drift, and temperature-induced changes to the shape and properties of the indenter tip. After characterizing and managing these complexities, quantitative mechanical property measurements are performed on a specimen of standard fused silica at temperatures up to 405 °C. The extracted values of hardness and Young's modulus are validated against independent experimental data from conventional mechanical tests, and accuracy comparable to that obtained in standard room-temperature nanoindentation is demonstrated. In situ contact-mode images of the surface at temperature are also presented.

NiCoCrAlYSiB coatings were deposited on the Co-based superalloy K40 by arc ion plating (AIP). The oxidation behavior of the bare alloy and of the coated specimens was tested in static air for 200 h at 1000 °C and 100 h at 1050 °C. The results showed that the oxidation rate of the system was greatly reduced by the addition of the NiCoCrAlYSiB coatings. Thin and adherent α–Al2O3 scales that formed on the coated specimens protected the substrates from further oxidation attack while non-protective oxide scales, mainly of Cr2O3 and CoCr2O4, appeared on bare K40 alloy. Element profiles on metallographic cross sections indicated that apparent interdiffusion occurred between the coatings and the substrates. The interdiffusion behavior and the resulting microstructure were investigated. As compared to aluminide coatings, NiCoCrAlYSiB coatings have less influence on the substrate microstructure.

Melamine (C3H6N6) was used as an additive for synthesizing aluminum nitride by combustion synthesis. It was found that at least 0.1 M of melamine addition to 1 M of aluminum and 0.8 MPa of nitrogen pressure were necessary to initiate a stable reaction. In addition to melamine, however, use of aluminum nitride as a diluent and application of forced nitrogen flow yielded better results. Analyzing the reaction temperatures, reaction rates, nitrogen contents, x-ray diffraction patterns, and scanning electron microscopy photographs, the optimum conditions for synthesizing AlN were established: (i) reactants were 90 wt% (1 M Al + 0.1 M melamine) + 10 wt% AlN diluent, (ii) chamber pressure was 0.9 MPa, and (iii) nitrogen flow rate was 15 l/min. Under these conditions, aluminum nitride with the stoichiometric nitrogen content of 34 wt% could be obtained.

AZ31 Mg machined chips were recycled by extrusion at 673 K with a low extrusion ratio of 45:1 and a high extrusion ratio of 1600:1. Oxide contaminants were dispersed more uniformly in the recycled specimen with the high extrusion ratio than in that with the low extrusion ratio. In tensile tests, the recycled specimens with the high extrusion ratio showed about 50% higher 0.2% yield stress and about 20% higher tensile strength compared with those of the reference specimens, which were the extruded AZ31 Mg blocks under the same conditions as the recycled specimens. The improvement of the tensile properties was attributed not only to the small grain size, but also to the dispersed oxide contaminants.

A metal-induced crystallization (MIC) technique was used to produce large-grain poly-crystalline silicon. Two sets of samples were prepared by first sputtering Al onto glass substrates. For one set of samples, hydrogenated amorphous silicon (a-Si:H) was sputtered on top of the Al without breaking the vacuum. For the second set, the samples were taken out of the vacuum chamber and exposed to the atmosphere to grow a very thin layer of native aluminum oxide before sputter depositing the a-Si:H. Both sets of samples were then annealed at temperatures between 400 and 525 °C for 40 min. X-ray diffraction patterns confirmed the crystallization of the samples. Scanning Auger microanalysis was used to confirm that the a-Si:H and Al layers exchanged positions in this structure during the crystallization process. Auger mapping revealed the formation of large grain poly-silicon (10–20 μm). A model is proposed to explain how the crystallization process progresses with anneal temperature.

Epitaxial films of rare-earth (RE = La, Ce, Eu, and Gd) tantalates, RE3TaO7 with pyrochlore structures were grown on biaxially textured nickel-3 at.% tungsten (Ni-W) substrates using chemical solution deposition (CSD) process. Precursor solution of 0.3∼0.4 M concentration of total cations were spin coated on to short samples of Ni-W substrates and the films were crystallized at 1050∼1100 °C in a gas mixture of Ar- 4% H2 for 15 to 60 min. X-ray studies show that the films of pyrochlore RE tantalate films are highly textured with cube-on-cube epitaxy. Improved texture was observed in case of lanthanum tantalate (La3TaO7) film grown on Ni-W substrates. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) investigations of RE3TaO7 films reveal a fairly dense and smooth microstructure without cracks and porosity. The rare-earth tantalate layers may be potentially used as buffer layers for YBa2Cu3O7-δ (YBCO) coated conductors.

Our concern here is to rationalize experimental observations of failure modes brought about by indentation of hard thin ceramic films deposited on metallic substrates. By undertaking this exercise, we would like to evolve an analytical framework that can be used for designs of coatings. In Part I of the paper we develop an algorithm and test it for a model system. Using this analytical framework we address the issue of failure of columnar TiN films in Part II [J. Mater. Res.21, 783 (2006)] of the paper. In this part, we used a previously derived Hankel transform procedure to derive stress and strain in a birefringent polymer film glued to a strong substrate and subjected to spherical indentation. We measure surface radial strains using strain gauges and bulk film stresses using photo elastic technique (stress freezing). For a boundary condition based on Hertzian traction with no film interface constraint and assuming the substrate constraint to be a function of the imposed strain, the theory describes the stress distributions well. The variation in peak stresses also demonstrates the usefulness of depositing even a soft film to protect an underlying substrate.

We have demonstrated previously, using nanoindentation, that the film thickness and substrate plasticity, the important two external variables in the film layer, control the failure of the film in a mutually exclusive way. In this work, we used a non-iterative Hankel transform method to analyze the stresses in an elastic film bound to an elastic substrate by a no-slip boundary condition and subjected to a Hertzian traction. We vary the substrate compliance by two orders of magnitude to generate interfacial mismatch stresses, which mimic the corresponding changes found in a real-life elastic film on an elastic-plastic substrate when the hardness of the substrate is changed. The analysis is found to reproduce faithfully the experimental trends, which showed that normal load and interfacial stresses generated by strain mismatch drive different modes of fracture depending on the film thickness in a mutually exclusive way. This validation paves the way for this theoretical technique to be used to design multilayered film structures.

The metastable solid solubility extension of CoO in ZnO (wurtzite) was investigated in precursor-derived powders as well as in thin films grown on sapphire substrates by pulsed laser deposition. A maximum solubility of 30% Co2+ in ZnO was achieved in the powders. Transmission electron microscopy (TEM) of the films revealed them to have grown epitaxially and retained up to nearly 40% CoO in solid solution, but some Co2+ precipitated as rock-salt. The temperature dependence of the metastable solubility limit in the ZnO–CoO system was assessed and is discussed in terms of the relevant thermodynamic factors. The magnetic properties of n-type conductive Zn0.79Co0.2Al0.01Ofilms were studied, yielding evidence of a ferromagnetic phase with a TC of 25 K and a second, magnetically ordered, phase with positive exchange and arguably a TC of ∼250 K. Connections between the properties and microstructural observations in high resolution TEM are proposed.

The affiliations for the authors were cited incorrectly in the November 2005 issue of the Journal of Materials Research. The correct affiliations appear above. The printer regrets this error.