Volume 104, Issue 2

Nanocomposites were prepared from 7475 alloy powder ball milled for 40 h with additions of 2 % Zr and 10 or 20 wt.% of ZrO 2 , Y 2 O 3 stabilized powders. Two types of ZrO 2 powder additions of size near 30 nm and 0.3–0.5 μm were used. Transmission electron microscopy studies confirmed the refinement of the aluminum solid solution grain size after milling, down to about 40 nm. The milled powders were consolidated using uniaxial hot pressing in vacuum at 380 °C and at a pressure of 600 MPa. The hardness of consolidated samples was higher for the 20 % ZrO 2 nanocrystalline ceramic powder addition than for 20 % ZrO 2 coarser powder, at 320 and 280 HV, respectively. Transmission electron microscopy studies allowed the determination of the grain size of aluminum solid solution to be near 100 nm after hot pressing and homogeneous distribution of ZrO 2 particles. The fractions of monoclinic ZrO 2 were similar in the milled powder and in the hot pressed samples. ZrO 2 nanoparticles did not retard the grain growth, contrary to 2 % of Zr which prevented grain growth during hot pressing. The compression tests showed 1 000 MPa of ultimate compression strength of samples with ZrO 2 nanoparticles, slightly higher than those with ZrO 2 larger particle additions.

The isothermal section of the phase diagram of the Al-Tb–V system at 773 K has been investigated by means of X-ray powder diffraction and scanning electron microscopy. The existence of 10 binary compounds and two ternary compounds, namely, Al 3 Tb, Al 2 Tb, AlTb, Al 2 Tb 3 , AlTb 2 , Al 10 V, Al 45 V 7 , Al 23 V 4 , Al 3 V, Al 8 V 5 , Al 43 V 4 Tb 6 and Al 20 V 2 Tb were confirmed. The compounds AlV, AlV 3 and Al 4 Tb were not observed, and no binary compound was found in the Tb–V binary system. The isothermal section consists of 15 single-phase regions, 30 binary-phase regions and 15 ternary-phase regions. The solubility of V in Al 2 Tb, AlTb and Al 2 Tb 3 is about 2.4 at.%, 1.6 at.% and 1.2 at.%, respectively. The solubility of Al in V is about 40.0 at.%.

An atomic mobility database for binary disordered and ordered fcc phases in multicomponent Al-Cu-Fe–Mg-Mn–Ni–Si–Zn alloys was established based on a critical review of diffusion data in various constituent binary systems via the DICTRA (DIffusion Controlled TRAnsformation) software package. The mobility parameters for self-diffusion in the metastable fcc structure were determined through a semi-empirical method. An effective strategy, which takes the homogeneity range and defect concentration into account, was used to optimize the atomic mobilities of L1 2 phase in the Fe–Ni system. Comprehensive comparisons between various calculated and measured diffusivities show that most of the experimental data can be well reproduced by the presently obtained atomic mobilities. The general agreement between the model-predicted concentration profiles and the experimental ones in the Al-Ni–Si, Al-Mg-Zn and Cu-Mn–Ni–Zn diffusion couples validates the potential application of the present atomic mobility database to predict the concentration profiles in higher order systems. An 8-elemental diffusion couple was also simulated with the present database.

Copper was electrodeposited at different current densities with additive modifications of the plating bath. With respect to applied current density there is modification of the microstructure as well as the physical properties of the copper deposit. There is notable change in cathodic potential, as revealed from polarization analysis, with Mw of poly ethylene glycol. The increase in current density increased crystallite size and increased the hardness of the deposit. There is significant change in grain size and shape with respect to applied current density in the case of the same kind of additives. The crystallographic orientation of the deposit has a prominent (220) plane for deposit at high current density and the ratio I (111) / I (220) decreased with increase in current density. The observed changes can be envisaged as due to the adsorption nature, nucleation characteristics with respect to various additives and also on the hydrogen evolution rate with applied current density, which influenced the deposit character.

FeCo alloy coatings were successfully prepared on carbon fiber surfaces by means of electroplating at 25 °C for 480 s. The structures and morphologies of the composite were characterized using X-ray diffraction and scanning electron microscopy. The coercivity ( H c ) and saturation magnetization ( H s ) of the FeCo/CF composites are 141.9 Oe and 100.5 emu · g −1 . The reflectivity of FeCo/CF composites is less than–5 dB over the range of 1.1 to 5.4 GHz. The reflectivity of FeCo/CF composites is less than–10 dB over the range of 1.6–2.1 GHz. The lowest reflectivity of the FeCo/CF composites is −14.7 dB at 2.0 GHz and the corresponding thickness is 3.3 mm.

SiBN has the advantages of Si 3 N 4 at high temperature and also presents good mechanical properties. Understanding the structural and mechanical properties of SiBN is essential in order to control the properties under fabrication. In this paper, the effects of BN content on structural and mechanical properties of SiBN ceramics were investigated using atomistic simulation. Phase separation of the SiN-rich region and the BN-rich region was observed for all the three compositions. With BN content increases, the BN-rich regions tend to be larger and the SiN-rich regions become smaller. Interestingly, Si 3 B 3 N 7 shows different structural and mechanical properties compared with Si 3 BN 5 and Si 3 B 5 N 9 : 1) sharper and narrower peaks for pair distribution functions and angular distribution. 2) larger values but less stability for Young's moduli at high temperatures. The larger Young's modulus of Si 3 B 3 N 7 is attributed to the network structure of BN and SiN phase.

Polycrystalline Ca 0.18 Sr 0.226 Ba 0.594 Nb 2 O 6 (CSBN18) was synthesized via the solid-state reaction route. X-ray structural studies confirmed it belonged to the tetragonal tungsten bronze family. Rietveld refinement of the X-ray data has been carried out for CSBN18 where the atomic positions and site occupancy factors for A-sites have been determined. The dielectric properties of CSBN18 ceramic were studied as a function of temperature in the 100 Hz–1 MHz frequency range. The dielectric relaxation followed the Vogel–Fulcher relation wherein E a = 37.4 meV; T f = 131.5 °C and ω 0 = 4.31 × 10 9 rad s −1 . A high pyroelectric coefficient of ∼ 250 μC m −2 .K was obtained around the transition temperature (∼150 °C). This is significantly higher than that reported for polycrystalline Sr x Ba 1-x Nb 2 O 6 (SBN). However, the piezoelectric coefficient ( d 33 ) of the title composition was as low as 6 pC N −1 .

As a high-dielectric cubic perovskite-related material, CaCu 3 Ti 4 O 12 (CCTO) has a dielectric constant of 10 4 at room temperature. Up to now the origin of the peculiar dielectric phenomena in CCTO is not fully understood and there are some disputes in the literature. In this paper, based a one-dimensional Ising model under static electric field, the dielectric properties of CCTO were studied. Results indicate that the theory is nearly consistent with the experiment.

Diffusion alloying processing is an emerging, environmentally friendly, surface engineering technique. In this study, we have utilized diffusion alloying processing to alloy aluminum and zinc mixed powder on pure magnesium for erosion wear protection. A stirring device was used for erosion testing. The treated and untreated samples were immersed in oil slurry and water slurry with quartz sand in suspension and rotated at a given speed. Scanning electron microscopy and X-ray diffraction were used to study the surface morphology and chemical composition of the coatings before and after erosion testing.

This paper presents the quality analysis of cladding layers deposited on continuous steel casting rolls made of 41CrMo4 (EN 10083-1-91). The effect of filler used on the tribological properties of claddings was analyzed. There was minimal mixing between the base material and interlayer observed in the process of hard surfacing. The microstructure of the interlayer and the coatings is martensite–ferrite. Dispersed carbides M C, M 7 C 3 , and Cr 23 C 6 were observed in the interlayer. Small amounts of carbides were also observed in the cover layer along with Cr 2 N and CrN, which was confirmed by energy dispersive X-ray analysis. The highest average hardness, 410 HV30, was measured in the cover layer at a distance of 1 mm from the surface. The lowest hardness was found in the base material, 239 to 243 HV30. The hardness of the interlayer metal is affected by mixing of cladding and cover layer metal. The cladding metal showed a martensite–ferrite structure and fine precipitates in the interlayer, and diffraction spectra of the carbides had the characteristics of M C, M 7 C 3 , and Cr 23 C 6 carbides. Lower abrasive wear has been reported in the reference material (a roll with a surface-hardened layer), which is in line with the contact surface hardness of test samples.

In this study, the machinability of austempered ductile iron with dual phase structure was investigated. Specimens were intercritically austenitized (partially austenitized) in the two phase region (α + γ) at various temperatures (810, 820 and 830 °C) for 90 min, then quenched in a salt bath held at austempering temperatures of 315 °C or 375 °C for 120 min and then air cooled to room temperature to obtain various ausferrite volume fractions and morphologies. Machinability tests were carried out at various cutting speeds (150, 180 and 210 m min −1 ), at a constant feed rate (0.30 mm rev −1 ) and depth of cut at 2 mm after austempering heat treatment. The experimental results showed that austempered specimens from the (α + γ) temperature range exhibited better machinability than as-cast samples. On the other hand, the cutting force was decreased with increasing proeutectoid ferrite fractions. The results also showed that continuity of ausferritic structure along intercellular boundaries plays an important role in determining machinability of austempered ductile iron with different ausferrite volume fractions. Another important result is that higher proeutectoid volume fraction has negative effects on surface roughness.

Copper oxide nanoparticles and submicron size spheres were produced via the ultrasonic spray pyrolysis method using copper nitrate without any additives. The effects of the process temperature and solution concentration on the copper oxide particles were investigated. HSC software, differential scanning calorimetry and thermal gravimetric analysis were used for the thermodynamic investigation of the CuO formation by the decomposition reaction. Particle characterization studies were performed using X-ray diffraction, energy dispersive spectroscopy, scanning–and transmission–electron microscopy. The results show that spherical CuO nanoparticles having around 80 nm particle size were prepared at 400 °C and the submicron size CuO spheres were obtained by the aggregation of nanoparticles at elevated temperatures. The crystallite sizes of the particles ranged between 21 and 46 nm.

Neodymium-doped yttrium aluminum garnet (Nd:YAG) ceramics were fabricated via a solid-state reaction method using high-purity Y 2 O 3 , Al 2 O 3 and Nd 2 O 3 powders as the raw materials. The mixed powder compacts were sintered at 1 750 °C for 5 h under vacuum. The Nd:YAG bulk without doped CaF 2 was opaque. A transparent Nd:YAG ceramic was obtained with tiny amounts of CaF 2 addition. The bulk had a uniform microstructure containing grains with an average size of 20 μm. No porosity could be detected in the sintered bulk. The maximum optical transmittance of the sample is 44 % in the visible range.

Multiferroic materials, which show simultaneous ferroelectric and magnetic ordering, exhibit unusual physical properties–and in turn promise new device applications–as a result of the coupling between their dual order parameters. BiFeO 3 is currently considered the most promising candidate material for device applications of room temperature multiferroics. However, its G-type antiferromagnetic behavior and high Néel temperature restrict the use of this material in potential applications. We report the synthesis and characterization of a novel Bi 2 FeNiO 6 material for the first time using a citric acid assisted gel combustion technique. Magnetization studies reveal that it exhibits ferrimagnetism with Néel temperature around 500 K. Differential scanning calorimetry study also reveals a sharp phase transition at 500 K. These materials also exhibit good ferroelectric behavior with square type hysteresis with a remanent polarization ( P r ) of 1.28 μC cm −2 , saturation polarization ( P s ) of 18 μC cm −2 and coercive fields 20 kV and–40 kV respectively. The results are convincing to make a big step towards developing devices that run on spin.

In this paper we demonstrate visible up-conversion emission of Er 3+ doped (Lu 0.5 Y 0.5 ) 2 O 3 nanophosphor and discuss possible mechanisms for pumping the upper energy levels of Er 3+ ions. Polymer complex solution synthesis yields well crystalline, pure-phase cubic nanopowder with particle size in the 20–50 nm range. Red, green and blue up-conversion emission is measured under near-infrared excitation (1 540 nm), over the temperature range 10–300 K. The red/green intensity ratio indicates that the mechanism responsible for populating red up-conversion is temperature dependent. Decay times are found to be around 0.25 ms for red and green, and around 70 μs for blue emission.