Volume 103, Issue 10

Phase equilibria of the Gd–Ni binary and Mg–Ni–Gd ternary systems were critically investigated using equilibrated alloys and differential scanning calorimeter measurements. The phase diagram of the Gd–Ni binary system was updated from scanning electron microscopy with energy-dispersive X-ray spectrometry, X-ray diffraction, and differential scanning calorimeter results obtained on binary samples over the entire composition range. Major changes made in the present work include the absence of the Gd 3 Ni 2 and GdNi 4 compounds and the congruent melting point of the GdNi compound. An isothermal section of the Mg–Ni–Gd ternary system at 673 K was constructed from the investigations on 22 ternary alloys. In total, six ternary compounds were identified in this work, three of which were observed to crystallize in the Cu 4 MgSn (τ1), Mo 2 FeB 2 (τ2), and Ru 4 Al 3 B 2 -type (τ3) structures, respectively. As in most of the Mg–rare-earth metal–transition metal ternary systems, a long-period-stacking ordered phase was identified to have an 18R structure and a melting temperature of 806 K. Noticeable solid solubility of Ni in the Mg 5 Gd and Mg 3 Gd binary compounds was observed.

A transformation of correlation functions used in the cluster variation method is introduced, such that the transformed correlation functions represent departures of the untransformed correlation functions from their values corresponding to ideal solutions. Analytical solutions for the transformed correlation functions and their derivatives with respect to composition in the infinite dilution limit are obtained for the first time for disordered binary bcc (under irregular tetrahedron approximation), fcc, and cph (both under tetrahedron-octahedron approximation) phases using the framework of the cluster variation method. These results are utilized to obtain the configurational contribution to self-interaction coefficients which occur in the expansion of the logarithm of the activity coefficient.

Both first-principles molecular-dynamics calculations and experimental observations reveal that the coherent Pd/TiAl interfaces with various orientations are all thermally stable after annealing at 773 K, which seems good for the lifetime of Pd/TiAl membranes. It is found that the bond strength of the Pd/TiAl interface at 773 K becomes slightly smaller than the corresponding value at 0 K, and the interface dipole formed at 773 K seems marginally smaller than that at 0 K. In addition, calculations also show that the bond lengths of Pd/TiAl interfaces after annealing at 773 K become oscillated due to thermal vibrations, which are quite different from those at 0 K.

The effects of electropulsing on microstructure changes and phase transformations of a tempered Mg-9Al-1Zn alloy sheet were investigated by using X-ray diffraction and transmission electron microscopy. The results indicate that with increasing frequency of electropulsing, precipitation and decomposition of β-phase were tremendously accelerated sequentially. The effects of electropulsing on single-point diamond turning processing were investigated by examining cutting force and surface roughness variations, and are discussed from the point of view of dislocation dynamics.

Based on indentation experiments under different loads, the mechanism of ductile-regime grinding of SiCp/Al composites has been investigated. The factors that influence the ductile-regime removal of SiC particles, such as tip radius of abrasive grains, intrusion depth, and volume fraction of SiC particles, have been analyzed by three-dimensional finite element simulation. The calculation results indicate that a sharp abrasive grain without tip radius cannot produce a plastic deformation region under the indenter and brittle fracture of the SiC particle takes place rather than ductile model of failure. The critical grinding depth of ductile-regime removal decreases with increasing tip radius of abrasive grains, but increases with decreasing SiC particle volume fraction.

The welding processes of three different magnesium alloys ZK60, AZ31, and Mg-rare earth alloy NZ30K were studied using a high-power CO 2 laser. The microstructure and tensile strength of welded joints were tested and analyzed. With increasing welding speed the tensile strength and total elongation of welded joints of ZK60 alloy are improved. The ultimate tensile strength of the welded joint of ZK60 is 211.18 MPa, 90% of the base metal. The tensile strengths of welded joints of AZ31 and NZ30K are better than those of the base metal. The expansion of the plasma of laser-welded ZK60 is the strongest with the highest temperature.

The pollution materials emission standards in Europe are going to be more strict. In order to meet the environmental standards, a European automotive manufacturer performs a finishing laser treatment on the honed cylinder bores of their V-engine blocks. Samples of laser treated cast iron cylinder bores with lamellar graphite were investigated. In order to evaluate the microstructure and grain size of the laser-treated layer, scanning electron micrographs were taken on cross-sectioned samples with a scanning electron microscope/focused ion beam dual-beam instrument. The samples were found to be ultra-fine grained. Nanoindentation hardness measurements of the surface layer showed a clear linear trend between the laser power density in the applied range and the measured hardness. Additional microhardness measurements suggest an annealed region beneath the surface.

In view of the recycling of aluminium scrap for automotive sheet application, we have investigated the solidification behaviour of AA5754 alloy containing additional amounts of impurity elements such as Si, Fe, and Cu. Ingot casts with a high impurity content resulted in coarse α-Al dendrites and complex-shaped secondary phases. A large volume of coarse Chinese script and needle-type Fe-bearing intermetallic phases were observed to form at the centre of an ingot. In addition to the grain-boundary eutectic, spherically shaped rosette-type eutectic phases were observed within the Al grain in the high-impurity alloy. The more uniform size distribution of the Fe-bearing intermetallics observed in the Al–Ti–B grain refined alloy is attributed to the presence of a large fraction of α-Al grain boundaries which distributes the eutectic liquid where the Fe-bearing intermetallic forced to nucleate and grow.

The structural evolution of nanocrystalline ZnO films on copper substrates synthesized via pulsed laser deposition was observed with increasing thickness controlled by deposition time. Scanning electron microscopy images indicate an increase in the average grain size. All the films are polycrystalline with the hexagonal wurtzite structure. X-ray diffraction patterns prove the orientation of the crystals to become better with an increase in film thickness. Raman measurements show three optical normal modes of crystalline ZnO indicating wurtzite structure. The line-width variation of the E 2 high mode reveals the structural improvement of the nanocrystalline ZnO films. The spatial correlation model was applied to analyze the structure evolution of the films. Different electron field-emission current densities are observed during the structural evolution of nanocrystalline ZnO films.

Porous cordierite–mullite ceramics with high strength were prepared by a pore-forming in-situ technique. The phase compositions, pore characteristics, and strength were investigated through X-ray diffractometry, scanning electron microscopy, and a microscopy measurement method. It is found that the sintering temperature strongly affects the formation of cordierite and mullite and the sintering, and thus changes the pore characteristics and strength. The formation of cordierite and mullite takes place on a large scale at 1430°C. The pore size distributions are bimodal in specimens sintered at 1370°C, 1400°C, and 1430°C, and mono-modal in a specimen sintered at 1450°C. The strength increases slightly when the sintering temperature increases from 1370°C to 1400°C, and increases significantly when the sintering temperature is increased to 1430°C. The most appropriate mode is a specimen sintered at 1430°C which has high cordierite (42 wt.%) and mullite content (53 wt.%), high apparent porosity (44%), high compressive strength (30.6 MPa) and a relatively homogeneous pore-size distribution.

Y 2 O 3 : Eu 3+ , Tb 3+ nanopowders were prepared via the sol–gel process, using yttrium pentadionate, europium, terbium nitrates, and ethanol as precursors. After the sol evaporation at 100°C, the formed gel was annealed from 300 to 900°C for 15 min, and the obtained nanopowders were analyzed by X-ray diffraction to characterize the microstructural behavior and the crystalline structure, which was determined as mainly cubic. The crystallite size varies from 8.6 to 30.9 nm, at 500 and 900°C, respectively. Transmission electron microscopy studies were carried out in order to analyze the microstructure and the size of crystallites. Three different Tb 3+ atomic contents (0.005, 0.075, and 0.01 at.%) were used at a fixed Eu 3+ level (2.5 at.%) with the aim of determining the relationship between the co-doping content and the scintillation intensity of the well-known 5 D o → 7 F 2 europium emission band at 611 nm. The results show that at higher Tb 3+ contents, a quenching process occurs between Eu 3+ and Tb 3+ ; however, even with the lowest Tb 3+ content (0.005 at.%), an increment on the scintillation light yield is observed compared with a Eu 3+ monodoped sample.

Silicon carbide coating was developed using chemical vapor deposition on carbon substrate as a protective coating. The present studies were carried out with methyl trichlorosilane as the SiC precursor, at 1673 K along with hydrogen and argon as carrier gas using a high-temperature vertical graphite reactor. The SiC coatings were characterized by means of X-ray diffraction for phase identification. Scanning electron microscopy analysis with energy dispersive X-ray spectrometer was also carried out for microstructure and elemental analysis. From the morphological study of different SiC deposits obtained at varying operating parameters it was observed that methyl trichlorosilane feed rate and hydrogen flow rate play a major role in deciding the nature of deposits and the argon percentage in the mixed gas also plays a vital role.

The adsorption and corrosion inhibition behavior of 1–tetradecylphosphonic acid self-assembled monolayers on the differently structured surfaces of 2024 and 1060 aluminum alloys were investigated by contact-angle measurement, potentiodynamic polarization, electrochemical impedance spectroscopy, and scanning electron microscopy coupled with energy-dispersive spectroscopy. The electrochemical experiments showed that a 4 h modification of 2024 and 1060 alloys resulted in a maximal inhibition efficiency. Independent of assembly time, the desorption of the tetradecylphosphonic acid molecules provoked by anodic polarization to a certain degree resulted in the acceleration of the anodic dissolution reaction. The inhibition of the self-assembled monolayers for the 1060 alloy was more prominent than for the 2024 alloy. This is consistent with the contact-angle values, supporting the conclusion that TDPA formed a more closely packed SAM on the surface of the 1060 alloy than of the 2024 alloy. Scanning electron microscopy/energy dispersive X-ray spectroscopy results directly revealed the inhibition effect of the monolayers on the primary corrosion stage of these two alloys.

Hydrogen gas is a clear energy resource. The hydrogen generation from the H 2 O/H 2 O 2 /MnWO 4 system was studied for the first time. The MnWO 4 powders were fabricated via an aqueous reaction method and followed by calcination at 400°C. The powders were characterized with X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectrometry. The efficiency of the hydrogen generation increased with increasing initial pH in the appropriate range, H 2 O 2 proportion, MnWO 4 proportion, and intensity of light resource. Calcining at 400°C for 1 h makes the MnWO 4 powder more effective for H 2 generation and more stable at higher initial pH. The MnWO 4 catalyst showed a long-term stability for photocatalytic H 2 generation. A mechanism of the hydrogen generation from the H 2 O/H 2 O 2 /MnWO 4 system is suggested.

Asphalt modification with polymers has utilized the advantages of nanotechnology including nanoclays as one of the components in addition to polymers. This led to the metamorphosis of polymer-modified asphalts into a new class of material called polymer-modified asphalt nanocomposites which offer the cumulative characteristic features obtained by the polymer modification of asphalt as well as the innovative properties experienced from polymer nanocomposites. Polymer-modified asphalt nanocomposites including styrene butadiene and ethylene vinyl acetate have revealed additional features which were not available in polymer-modified asphalts. The compositional complexity provides a great challenge in addressing the structure–property relations prevailing in these materials. This paper describes microstructural features as determined by Qwin Plus Software analysis and the rheological properties on compositional changes.

The microstructure of the as-cast Mg-3.1Nd-0.45Zr-0.25Zn (wt.%) alloy was investigated. It consists of α-Mg matrix, a divorced intergranular phase and small Zr-containing particles. Scanning electron microscopy equipped with energy dispersive spectroscopy analysis on transmission electron microscopy samples was carried out in order to eliminate the Mg matrix contribution to the quantitative analysis results and to reveal the intergranular phase composition which was found to be Mg 12– x Zn x Nd ( x ∼ 0.31) (space group I4/mmm) with a bct crystal structure. The lattice parameters ( a = 1.029 nm and c = 0.591 nm) were found using X-ray diffraction with the least squares refinement technique. The combination of different characterization techniques indicates that Mg atoms are substituted by Zn atoms without a change in the crystal structure.