Volume 102, Issue 2

The activities of zinc, a Zn , and magnesium, a Mg , from very low to high temperatures in the Mg–Zn binary system were evaluated for the first time from the relationship between the Gibbs energies of formation, δ f G¯ o T , of Mg 48 Zn 52 , Mg 2 Zn 3 , MgZn 2 and Mg 2 Zn 11 and their phase equilibria. The δ f G¯ o T values adopted were determined in our previous calorimetric studies. It was found that the a Zn and a Mg values in the compounds steeply changed from the minimum to maximum as a function of the composition in a narrow solubility range. Such a change was more emphasized toward low temperatures (3 K). Since one of the dominant factors for the composition change in a narrow solubility range in Mg 48 Zn 52 and Mg 2 Zn 3 is the formation of vacancies at the Zn site, the relative partial molar Gibbs energies of the vacancy formation, δ G Zn vacancy Zn , were estimated from the obtained a Zn values. At 298 K, the δ G Zn vacancy Zn values of Mg 48 Zn 52 and Mg 2 Zn 3 were 73.5 and 344.3 kJ mol −1 , consistent with about the same order of the enthalpy of the vacancy formation in Ni 3 Al (= 173.7 kJ mol −1 ) as determined by positron annihilation spectroscopy. When the symmetric atomic configuration at the stoichiometric composition was violated by the formation of vacancies, the change in relative partial molar value of lattice defects was found to be large.

The phase equilibria and liquidus temperatures in the ZnO–“FeO”–Al 2 O 3 –CaO–SiO 2 system in equilibrium with metallic iron have been determined experimentally in the temperature range 1343 to 1553 K and for compositions relevant to a number of different non-ferrous smelting slags. The results are presented in the form of a pseudo-ternary section ZnO–“FeO”–(Al 2 O 3 + CaO + SiO 2 ) with CaO/SiO 2 = 0.55 and (CaO + SiO 2 )/Al 2 O 3 = 7.0. It was found that wustite and spinel are the major primary phases in the composition range investigated. Wustite (Fe 2+ , Zn)O and spinel (Fe 2+ , Zn)O · (Al, Fe 3+ ) 2 O 3 solid solutions are formed in this system, and the ZnO in slag partitions preferentially to the spinel phase.

Aluminum-doped zinc oxide thin films have been fabricated by reactive mid-frequency magnetron sputtering from Zn/Al metallic targets (Al 2 wt.%) with a dual magnetron (TwinMag™) configuration. The dependence of the structure, composition, electrical and optical properties of the films on the oxygen partial pressure has been investigated. It is shown that films with low resistivity and high optical transmittance could only be deposited under a narrow range of oxygen partial pressure. The film prepared at a partial pressure of 25 mPa exhibited highly c -axis oriented growth and a lowest resistivity of 4.6 · 10 −4 Ω cm.

This paper describes the definitions and differences of the computational methods of virial stress and engineering stress in nano-scale problems. According to simulation results of tensile testing of a single-crystalline nano-scale copper bar, the average stresses in a cross-section of the copper bar, calculated with different methods, are compared. The values and distributions of local tensile stresses reveal further insights into these two methods. The advantages and disadvantages of these two methods are also discussed in detail.

SnO 2 –NiO and SnO 2 –CoO powders mixed in a molar ratio of 92: 8 were reactively sintered for up to 200 h at 1400 °C to form composites having NiO and Co 2 SnO 4 particles embedded in Ni- and Co-doped SnO 2 grains, respectively. Analytical electron microscopic observations indicated the embedded particles remained nonepitaxial with respect to the host grains despite prolonged holding at a high homologous temperature, owing to a rather limited solid solubility and vague interfacial energy cusp. Upon cooling or solution annealing at 900 °C, the Niand Co-doped SnO 2 formed {100}, {110}, {101} and/or (001)-specific Guinier–Preston zone plates and dislocations. The formation of additional commensurate superstructure in Ni- but not Co-doped SnO 2 indicated a coupled atom clustering and ordering process for the former during solution annealing.

Mechanical alloying of mixed powders is of great importance for preparing oxide dispersion strengthened ferritic steels. In this study, the microstructual evolution of ferritic steel powder mixed with TiH x , YH 2 and Fe 2 O 3 in the process of mechanical alloying is systematically investigated by using X-ray diffraction analysis, scanning electron microscopy, transmission electron microscopy and microhardness tests. It is found that titanium, yttrium hydrides and iron oxide are completely dissolved during milling, and homogeneous element distribution can be achieved after milling for 12 h. The disintegration of the composite powder particles occurs at 24 h and reaches the balance of welding and fracturing after 36 h. The oxygen content increases sharply with the disintegration of powder particles due to the absorption of oxygen at the solid/gas interface from the milling atmosphere, which is the main source of extra oxygen in the milled powder. Grain refinement down to nanometer level occurs due to the severe plastic deformation of particles; however, the grain size does not change much with further disintegration of particles. The hardness increases with milling time and then becomes stable during further milling. The study indicates that the addition of iron oxide and hydrides may be more beneficial for the dispersion and homogenization of chemical compositions in the powder mixture, thus shortening the mechanical alloying process.

Strips of AZ31 were produced by Direct Strip Casting and subsequent hot rolling at 400°C. The texture and microstructure of the strips in as cast and hot rolled condition were investigated. The cast strip exhibited a random distribution of the grain orientations while a strong basal-type texture was observed in the hot rolled sheets. The flow curves of the Direct Strip Cast material were obtained by hot compression experiments and dynamic recrystallization was found to occur at all studied temperatures and strain rates. The tensile properties of strip cast and hot rolled magnesium were examined by tests at room temperature. Grain refinement and the development of the basal texture during hot rolling resulted in high strength of the hot rolled magnesium sheet.

Development of cube texture ({001}〈100〉) has been investigated in pure Ni (99.97%) deformed to ultrahigh straining (e = 6.4) by accumulative roll bonding and then annealed at different temperatures for use as coated superconductor substrate. The as accumulative roll bonding processed sheets reveal a typical pure metal or copper type homogeneous deformation texture. After annealing at different temperatures, strong cube texture formation is observed and a nearly 100% cube textured tape with almost twin-free microstructure is obtained after annealing at 800°C for 1 h. The development of a sharp cube texture is accompanied by the development of a predominantly low angle boundary network. The very sharp cube texture formation in this material appears to be due to the oriented nucleation of cube grains at early stages of recrystallization and selective growth of these grains with progressing recrystallization. The results obtained indicate that accumulative roll bonding could be a very attractive route for fabricating highly cube textured superconductor substrate tapes from Ni.

Sol-gel prepared Ba 0.6 Sr 0.4 TiO 3 (BST) thin films were prepared on platinized silicon substrate and annealed by rapid thermal annealing at temperatures ranging from 650 °C to 850 °C. X-ray diffraction, atomic force microscopy and electrical measurements were used to investigate the temperature dependence of the structural and physical properties of Ba 0.6 Sr 0.4 TiO 3 thin film. The dielectric constants of BST samples annealed at 700 °C and 750 °C, measured at zero-bias electric field, are 166 and 193, respectively. It is found that all the prepared BST films show Ohmic-like conduction at low voltages except for the 650 °C annealed BST sample, for which Ohmic conduction covers the whole measured voltage range; BST films annealed at 700 °C, 750 °C and 800 °C demonstrate Poole–Frenkel emission conduction at high voltages, while BST film annealed at 850 °C presents Schottky emission behavior.

Tubular ZnO clusters and rods have been fabricated using a simple template-free hydrothermal method by controlling the reaction temperature, pH value and reaction time. The obtained ZnO products were characterized using scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, photoluminescence spectra and UV-vis diffuse reflectance spectroscopy. The results show that the formation of the tubular ZnO clusters and rods involves both a growth process and a dissolution process. The reaction temperature and reaction time play important roles in the formation of the ZnO clusters and rods with tubular morphologies. The possible formation mechanism of tubular ZnO is discussed.

In this study, titanium dioxide (TiO 2 ) nanofibers with diameters ranging from 200–500 nm are successfully prepared via an electrospinning technique using a solution that contains polyvinyl pyrrolidone (PVP) and tetrabutyl titanate (TBT). Three key processing parameters are evaluated on the morphology of the fibers formed. Firstly, the PVP: TBT molar ratio is strongly correlated with the morphology of the fibers formed, and two extremes in the fiber morphology are observed as a result of varying the PVP: TBT molar ratio. Secondly, the electric field strength has been found to most strongly affect the fiber diameter, which increases as the electric field strength increases. Thirdly, the electrospun TiO 2 /PVP composite nanofibers are calcined at different temperatures. The process of removing organic components, the phase formation and the phase transition of the inorganic TiO 2 are investigated using thermo-gravimetry–differential scanning calorimetry, infra-red and X-ray diffraction analyses.

A simple to implement and original automated method is presented to quantify the intensity and wavelength of “banded structures”, i. e. microstructures presenting irregular and parallel bands enriched in a given phase. This method is based on the analysis of the covariance function of binary images. It is firstly tested on model representative images. It is compared with a conventional method derived from the ASTM E-1268 standard and appears to present a higher robustness with regard to preparation artifacts. Then, it is applied to real microstructures of dual-phase steels, which show more or less regular martensite-enriched bands in a ferrite matrix. The method is capable of efficiently discriminating dual-phase microstructures resulting from different thermo-mechanical routes.

This work describes the nature of anisotropy in mechanical properties of three alloys, namely Ti-8Nb, Ti-12Nb and Ti-16Nb in the hot rolled condition. The work hardening curves of the alloys Ti-8Nb and Ti-12Nb exhibit a single slope and follow the Ludwik relation. The alloy Ti-16Nb displays two slopes in work hardening curves. This indicates that two different mechanisms are operative during tensile testing. The work hardening curves follow a modified Ludwik equation. The alloy Ti-16Nb exhibits the lowest anisotropy index and percentage in plane anisotropy. The alloy Ti-12Nb exhibits the highest values of both the anisotropy index and percentage in plane anisotropy. The low percentage in plane anisotropy of the alloy Ti-16Nb has been attributed to the presence of fibre textures. The yield loci of the hot rolled alloys have been determined using the Knoop hardness method. The results show that hot rolling induces anisotropy in yield strength and changes the shape and size of yield locus plots.

Microstructural evolution of AZ80 magnesium alloy during multi-directional compression deformation at elevated temperature was systematically investigated. The effects of deformation variables on the as-compressed microstructures and the deformation behavior were analyzed. Grain splitting that developed in various directions due to the formation of microbands was the main characteristic of microstructural evolution during hot multi-directional compression, which was different from that of the continuous uniaxial compression. Such microbands intersected each other, resulting in continuous subdivision of the coarse grains into misoriented fine domains, thus contributing to grain refinement. Further deformation led to increases in the number and misorientation of these boundaries and finally almost full development of fine equiaxed grains at high strain. A more homogeneous microstructure with fine dynamic recrystallization grains could be attained with the applied strain up to a critical strain, and after that, it was difficult to achieve further grain refinement. However, the higher reduction in each pass and the lower deformation temperature in the certain range aided grain refinement. The second phase Mg 17 Al 12 with large particle size that remained after solution treatment experienced a series of changes with the process of breaking up, dissolving, precipitating and then re-dissolving. Fine precipitates were located at the grain boundaries, suppressing dislocation movement and preventing grain growth.