Volume 110, Issue 8

Based on a current non-equilibrium dendrite growth model and a local non-equilibrium solute trapping model for dilute alloys, a model for rapid dendritic solidification of dilute alloys was developed. In the present work, we considered the results of the non-equilibrium dendrite growth model for solidification of dilute undercooled melts with different concentrations in order to reveal the concentration effect. Incorporating the fluid flow effect, we applied an extended chemical superheating model to predict the dendrite remelting of dilute undercooled melts. This model predicted that the dendrite remelting will disappear abruptly once the dendrite growth velocity exceeded the solute diffusion velocity in the liquid phase at the interface.

In pure magnesium and aluminum-containing magnesium alloys, the microstructure also plays a role in the corrosion properties. In Part 1, the grain sizes, secondary dendrite arm spacings ( SDAS ) and precipitates of β phase were determined by casting samples with 0, 3, 6, 9 and 12 % aluminum (all compositions in mass percentage) at different cooling rates. These samples were tested for corrosion properties by immersion and salt spray tests. The modeling of the corrosion process enables establishing a mathematical link between the microstructure and corrosion properties of an alloy. The results show an increase in the corrosion rate with increasing aluminum contents and the cooling rate. The precipitations at the grain boundaries have a relevant impact on corrosion properties of the magnesium–aluminum alloys. A random comparison using the salt spray test tends to confirm the results.

Ce 2 (MoO 4 ) 3 is a harmful phase formed in waste glasses from nuclear fuel. To determine the third-law entropy of Ce 2 (MoO 4 ) 3 , the isobaric heat capacities, Cp,m°$C_{p,m}^^\circ $, were measured with a relaxation-method instrument at 2–300 K. The standard entropy, Δ0TSm°$\Delta _0^TS_{\rm{m}}^^\circ $, at 298.15 K was determined with fitting functions including the Debye–Einstein formula including electronic and spin-wave terms. The Néel temperature, T N , was estimated by extrapolation from the magnetic term in this fitting function. The phase stability of Ce 2 (MoO 4 ) 3 is discussed in terms of its standard Gibbs energy of formation, ΔfGm°${\Delta _f}G_{\rm{m}}^^\circ $, which was derived by combining the values for Sm°$S_m^^\circ $determined in this study with reference data for the standard enthalpy of formation, ΔfHm°${\Delta _f}H_{\rm{m}}^^\circ $.

Springback caused by elastic recovery is known to be a major disadvantage in sheet metal forming. Many studies focused on the prediction and compensation of springback in the bending process have used simulation and numerical methods, with experimental tests rarely being reported. A new approach, aimed at decreasing springback, is presented in this paper to solve the springback problem and provide a reference for other researchers. A new edge bending method called “incremental bending” has been developed and implemented on aluminum sheet at room temperature. Using this method, bending strain was lowered, leading to a reduction in springback. 3D Digital Image Correlation, an optical measurement technique, was adopted simultaneously to provide a high accuracy measurement of the full field strain distribution and springback curvature, making it very suitable for springback measurement. The experimental results show an obvious reduction of springback, which agrees well with the theoretical analysis. This work could help to minimize springback in sheet metal bending dramatically and improve formability and productivity, as well as provide a reference for researchers studying cold-bending. Details of the basic bending theory, experimental method, experimental results, and analysis will be demonstrated in the following content.

This study investigates how minor La and Ce additions affect the microstructure and mechanical properties of A201 alloy. The results indicate that adding 0.2 wt.% La or Ce to A201 alloys could refine the grain size and led to a rise in the temperature of exothermic peak of Ω and θ' precipitates. In addition, the presence of La-rich phase or Ce-rich phase consumed the quantities of Cu atoms in the Al matrices during solidification. Neither of the phases could be dissolved during solution heat treatment, reducing the precipitation of Ω and θ' phases in A201 alloy after artificial aging heat treatment. The lower volume fraction of the Ω and θ' strengthening phases led to a decrease in hardness and tensile properties but an increase in ductility of the La-containing or Ce-containing A201 alloy.

Laminated sheets with Ti 2 AlC/TiAl composite layers synthesized from the Ti–Al–TiC system and TC4 titanium alloy as the toughening layer were fabricated by spark plasma sintering. Their phase composition and microstructure were analyzed and flexural strength and fracture toughness measured. The composite layers mainly comprised Ti 2 AlC, TiC, TiAl, and Ti 3 Al phases. The flexural strength and fracture toughness of the sheets perpendicular to the laminated direction were 455.74 MPa and 21.65 MPa · m 1/2 , respectively. The TC4 layers provided a strengthening–toughening effect by changing the crack propagation model and weakening the fracture energy. Ti 2 AlC particles provided a strengthening effect. The synergistic effect of the two components enhanced the mechanical properties of these TiAl-based laminated composite sheets.

Fractal theory is widely used to analyze the topography of surfaces; however, the relationship and characteristics of fractal dimension and microstructures of β-SiC films have not been reported. Using scanning electron microscopy and computer analysis, the microstructures of β-SiC films were evaluated; the films were prepared on AlN substrates by laser chemical vapor deposition using a diode laser and hydrido polycarbosilane as the precursor at different vacuum levels. The effect of vacuum level on the microstructure of β-SiC films was evaluated. The results show that the microstructures of β-SiC films exhibit the characteristics of fractals. Using the box counting method, the fractal dimensions of β-SiC films were calculated to be about 1.94–2.14, providing more fractal identification in evaluating the performance of films.

La 2 (Zr 0.7 Ce 0.3 ) 2 O 7 ultrafine powder was prepared via a precipitation process using ZrOCl 2 .8H 2 O, Ce(NO 3 ) 3 .6H 2 O, and La 2 O 3 precursors. The thermal behavior, phase structure, particle size, and morphology of the nanostructured precipitate and the calcined powders were investigated. The thermal analysis results of the nanostructured precipitate showed that pyrolysis occurs at 600 °C. The X-ray diffraction analysis results of the calcined powders indicated that submicrometer crystalline phases of lanthanum zirconate pyrochlore and lanthanum cerate fluorite with approximately 50 % amorphous were formed at 1 100 °C. The powders calcined at 900 °C were composed of semi-crystallized nanoparticles including crystalline phases of lanthanum zirconate and cerate. The semi-crystallized nano-particles can potentially be used as raw material of new nanostructured thermal barrier coatings.

Several phosphate-bonded castables were prepared using corundum as a raw material and 48 wt.% phosphoric acid as a binder. The phase composition, microstructural evolution, and properties of the castables samples were analyzed, and a relationship between the microstructures and properties of the castables was established. The results revealed that the cold modulus of rupture of the specimens increased by 19 % to 33.02 MPa after firing at 1 100 °C when the alumina micropowder content increased from 10 % to 15 %. X-ray diffraction analysis revealed that corundum and AlPO 4 were present in the castables fired at both 1 100 °C and 1 500 °C. The intensities of the AlPO 4 diffraction peaks increased as the alumina micropowder content and sintering temperature increased. Scanning electron microscopy revealed that AlPO 4 was tightly arranged and packed with particles.

The electrokinetic behavior of TiO 2 –WO 3 nanoparticles while applying non-uniform AC electric fields at a frequency of 10 kHz was investigated using planar parallel electrodes. For this purpose, WO 3 and TiO 2 nanoparticles, which exhibited a different response to the applied electric field, were deposited simultaneously at 10 kHz. Characterization of the obtained patterns by optical and scanning electron microscopy revealed that the TiO 2 nanoparticles, which were unable to enter the gap, moved toward it and got deposited there in the presence of WO 3 nanoparticles. Hence, a composite layer consisting of TiO 2 and WO 3 nanoparticles was formed in the gap. A hypothesis for the change in the deposition and electric behavior of TiO 2 nanoparticles is presented in this paper using the multi-shell model. Furthermore, a possible method for the fabrication of a TiO 2 –WO 3 based gas sensor has been provided.

In this study, 3-dimensional nanoflower structured TiO 2 photoanodes were successfully grown onto tin oxide doped with fluorine substrates. X-ray diffraction and scanning electron microscopy were performed. The 3-dimensional TiO 2 nanoflowers presented improved photoelectrochemical performance compared with a TiO 2 layer. Meanwhile, TiO 2 nanoflowers with 2.5 h preparation time substantially increased the production of H 2 compared with the TiO 2 layer. The improved performance could be ascribed to the 3-dimensional nanoflower structure with many carriers and fast reaction kinetics, which enhanced light absorption and enlarged the contact area between the photoanode and electrolyte. Moreover, this nanoflower structure with trunks connected to the FTO substrate also improved the transfer of photogenerated carriers.

Al 2 O 3 based self-lubricating ceramic tool materials with the addition of CaF 2 @Ni–B were prepared using the vacuum hot-pressing technique. The microstructure, mechanical properties and cutting performance of the material with different contents of CaF 2 @Ni–B were studied. Compared to its counterpart tool material without CaF 2 @Ni–B, the fracture toughness and flexural strength of the Al 2 O 3 /TiB 2 /(CaF 2 @Ni–B) self-lubricating ceramic tool materials increased by 40.5 % and 10.1 %, and the tool life increased by 25 %.