Volume 103, Issue 11

Experimental characterization of microstructure evolution in three binary Al–Li alloys provides a quantitative test of diffusion screening theory. Particle size distributions, growth kinetics, and maximum particle sizes are obtained through quantitative, centered dark-field transmission electron microscopy. The dependences on δ′ precipitate volume fraction of the coarsening rate constant and maximum particle size are revealed, both of which have eluded determination for a half century. These experiments show that the diffusion screening theory for late-stage phase coarsening yields accurate predictions of maximum size of particle and relative coarsening constant.

The Mg–C binary phase equilibria and thermodynamic data are critically evaluated in this work. The necessity is demonstrated to meticulously evaluate the original experimental literature instead of relying on erroneous statements in a previous review that had led to a completely different phase diagram. The two Mg carbides, Mg 2 C 3 and MgC 2 , are both shown to be metastable based on the examination of the thermodynamic data and the original experimental work on their formation and decomposition. Using the Calphad method, a thermodynamic description of the Mg–C system is developed. The stable phase diagram at 1 bar was calculated without assuming any binary interaction parameters. The solubilities of C in liquid Mg, having recently been measured to be tens of ppm between 800°C and 900°C, verify the calculated phase diagram. The metastable Mg 2 C 3 and MgC 2 phases were also modeled and their descriptions were directly derived from the thermodynamic data. The complete Mg–C description allows the calculation of metastable phase equilibria involving these carbides by suspending graphite and diamond.

Six {Ni-30 wt.% Cr}-based alloys containing from 2.5 to 5 wt.% C, were elaborated by casting and heat treated at 1000, 1100, and 1200°C for 50 h to achieve stabilization. Their melting ranges and the phase surface fractions were established. These results were compared to thermodynamic calculations. All microstructures are hyper-eutectic and carbides are either Cr 7 C 3 or Cr 3 C 2 . The carbide fraction increases with the carbon content and graphite appears for carbon contents higher than 4 wt.% C. The experimental solidus and liquidus temperatures are several tens of degrees lower than the calculated ones but their evolution versus the carbon content are well represented by calculations. There is a good agreement between experiments and calculations concerning graphite. The hardness is about 300 HV and decreases when the heat-treatment temperature increases.

The aim of the presented experimental and numerical investigation is to verify the ternary phase diagram Cu–Sn–P in the Cu-rich corner, especially the presence and position of the ternary eutectic transition point. Annealing experiments within a concentration gradient have been performed and compared to computational thermodynamics. The identification of phases and phase regions is based on differential thermal analysis, scanning electron and light microscopy. The discussed ternary eutectic transition in the Cu-rich corner is confirmed, phases and phase regions, as proposed by computational thermodynamics, are verified. In addition, the existence of the γ phase was confirmed but the ∊ phase was not found in the as-cast microstructures which decreases its importance for technical bronze alloys with Sn up to a mass fraction of 0.2.

The response of a strong bainitic-steel to tempering at high temperatures is investigated, because a softened state is sometimes necessary during the manufacture of engineering components, prior to the final heat-treatment which hardens the material. Thermodynamic calculations conducted to determine the maximum temperature at which the steel could be annealed without forming austenite were found to significantly overestimate the actual temperature at which austenite, ferrite and cementite (γ + α + θ) can coexist in equilibrium. As a consequence, the tempering temperature must be limited to below about 700°C, which unfortunately necessitates many days of tempering in order to reduce the hardness to < 250 HV. An alloy modification which may shorten this tempering time is suggested. One unexpected outcome is that the unintended heat treatment in the three-phase field revealed useful information about the nucleation of pearlite on cementite particles. Colonies of pearlite started inevitably on particles of cementite located at the γ / α interfaces, rather than at similar particles enclosed completely by the austenite.

A comparative study of the microstructure, compressive properties, and fractography of Ti 3 Al and Ti 3 Al–Nb intermetallics produced via powder metallurgy and standard vacuum melting and casting processes has been carried out. Non-porous compacts were obtained via vacuum hot pressing of powders produced by mechanical alloying. Prior to compression tests, all samples were homogenized by a solution treatment at 1050°C (α + β region), followed by water quenching. The compression tests were performed from room temperature to 500°C in vacuum at a strain rate of 2.4 × 10 –3 s –1 . Detailed microstructural characterization was conducted using scanning electron microscopy, followed by energy dispersive X-ray spectroscopy and X-ray diffraction analysis. Values of compressive mechanical properties of compacts were higher than those of castings. Fracture topography was examined by scanning electron microscopy. A correlation between ductility and the fracture mode exists for all materials.

Sn-1wt.%Cu hypereutectic alloy was directionally solidified upward at a constant temperature gradient ( G = 12 K · mm –1 ) in a wide range of growth velocities ( V = 1–250 μm · s –1 ) using an improved Bridgman-type directional solidification furnace. The microstructure was observed to be a Cu 6 Sn 5 rod in the matrix of β-Sn from the directionally solidified Sn-1wt.%Cu samples. The rod spacing (λ), rod diameter ( d ), and microhardness ( H V ) were measured from transverse sections of the samples. The experimental results showed that the rod spacing and rod diameter decreased with increasing growth velocity, while the microhardness increased with increasing growth velocity. The dependences of the rod spacing ( λ ), rod diameter ( d ), and microhardness ( H V ) on the growth velocity ( V ) were determined by using linear regression analysis, given as: λ = 10.49 V −0.47 , d = 2.1 V −0.37 and H V = 9.33 V 0.11 , respectively. The dependences of the microhardness on the rod spacing and rod diameter were also investigated, and the relationships between them were obtained by using linear regression analysis, given as: H V = 16.4λ −0.235 and H V = 11.8 d −0.245 .

Si 3 N 4 ceramics reinforced with SiC particles were fabricated via spark plasma sintering at 1650°C under 40 MPa pressure. AlN and Y 2 O 3 were used as sintering additives. The purpose of this work was to study the influence of SiC powders on the properties of Si 3 N 4 /SiC composites. The microstructure, phase composition, and mechanical properties of the composites were investigated. It was found that mechanical properties of the composites improved, the α–β transformation and grain growth of β-Si 3 N 4 were inhibited and the equiaxed grain increased due to the increase of SiC (w) .

The present work was carried out to compare the formation of single icosahedral phase during conventional heating and microwave processing. Al 67 Cu 23 Fe 10 alloy powder was synthesized from high purity (99.9%) powder elements by mechanical alloying. Differential scanning calorimetry combined with in-situ synchrotron energy dispersive X-ray diffraction was used to identify the main solid state reactions and the phase evolution of the powders. Inductive microwave processing in the magnetic field anti-node was performed to obtain the quasicrystalline phase in only a few seconds. Due to the rapid cooling of the sample it was possible to stabilize the icosahedral phase against its competing quasicrystalline approximants. Laboratory X-ray diffraction analysis was used to characterise the atomic structure of the specimen and scanning electron microscopy was used to characterise the microstructure after the microwave processing.

The characteristics of both direct and converse magnetoelectric (ME) interactions in bilayer composite structures comprising layers of a commercially available magnetostrictive permendur CoFe alloy and different piezoelectric PZT ceramics are investigated in detail by the method of harmonic field modulation. It is shown that, given the optimum DC magnetic bias field, a high piezomagnetic coefficient in the alloy leads to increased efficiency of ME interactions. The resonant behavior of frequency dependencies of the magnetoelectric voltage is explained by excitation of bending and planar mechanical oscillations in the structures. The results are of interest for developing highly sensitive AC magnetic field sensors and magnetoelectric transducers for energy harvesting from mechanical vibrations.

A WE54 (Mg–Y–Nd–Zr) magnesium alloy was subjected to uniaxial and plane strain compression at two temperatures (300 and 400°C) and two strain rates (10 –4 and 10 –2 s –1 ). This processing resulted in a relative weakening of the initial strong basal texture of the as-received material. Contrarily to the conventional AZ31 alloy, the deformation texture was more or less insensitive to the processing parameters but depended strongly on the hot deformation type. Annealing treatments at 450°C up to 7 days resulted in normal grain growth. The grain growth annealing caused dissolution of the precipitates that had developed during hot deformation at 300°C. The grain growth kinetics can be described by D n = D R n + kt , where n was found to range between 6 and 11. A net randomization of the texture was evidenced for all the deformation conditions.

Based on the flow formulation for rigid–plastic/viscoplastic materials, a rigid–plastic/viscoplastic element-free Galerkin method is established to realize the simulation of massive metal-forming processes. Stiffness equations and solution formulae are derived in terms of the incomplete generalized variational principle. The transformation method is employed to exert the essential boundary condition in the local coordinate system. The arctangent frictional model is used to implement the frictional boundary conditions, and the transform matrix from the global coordinate system to local coordinate system is given. Being similar to finite-element simulations, the key techniques for metal-forming meshless analysis such as the treatment of the rigid region, dynamic adjustment of the boundary nodes, and treatment of volumetric locking are developed. The analysis software is developed. The equal-channel angular pressing process is simulated numerically using the software. The effective strains become larger and more uniform with increasing curve angle Ψ. On the other hand, the forming load increases greatly with the increase in the curve angle Ψ. The effective strains change slightly with the change of the frictional status between the die and the workpiece. However, the frictional status influences greatly the forming load.

A reliable finite element model was employed to investigate the effects of configuration parameters and impact velocity on the in-plane deformation mode and dynamic plateau stress of staggered triangular honeycomb cores at impact velocities 3–300 m s –1 under in-plane crushing loadings. At different impact velocities, ‘>’-, ‘<’-shaped, and ‘I’-shaped deformation modes appear in turn. The effects of configuration parameters on the deformation modes are discussed qualitatively. When all configuration parameters are kept constant, the mean in-plane dynamic plateau stress is proportional to the square of impact velocity; for a given impact velocity, the mean in-plane dynamic plateau stress is related to the ratio of cell-wall thickness to edge length by power laws and to the expanding angle by complicated curves. Mean in-plane dynamic plateau stresses are expressed by empirical equations in terms of configuration parameters and impact velocity based on our simulation results.

Polyaniline/Fe 3 O 4 nanocomposite was synthesized via micro-emulsion polymerization of aniline in the presence of Fe 3 O 4 nanoparticles. The experimental results revealed that a core-shell structure composite was obtained successfully. Electrospinning of Fe 3 O 4 -polyaniline/polyacrylonitrile (Fe 3 O 4 –PANI/PAN) blended with different composition ratios were performed using N, N-Dimethylformamide as solvent. Morphology and fiber diameters were investigated by means of scanning electron microscopy. Electrospun fibers with diameters ranging from 168 to 300 nm were obtained. Scanning electron microscopy images indicated that the diameter of the composite nanofiber increases with the content of Fe 3 O 4 . It was also found that the permittivity was decreased by the addition of Fe 3 O 4 , but the permittivity was increased relevantly if the Fe 3 O 4 mass fraction in the Fe 3 O 4 /PANI was increased. The thermal stability of the composite nanofibers is also examined in this paper.

Gelatin–Cloisite 30B (C 30B) hybrid nano-composites were prepared by blending gelatin with cloisite 30B in aqueous solution. The nano-composites were characterized by using FTIR, SEM and XRD analysis. From the FTIR spectra the various groups present in the gelatin blend were monitored. The homogeneity, morphology and crystallinity of the blends were ascertained from SEM and XRD data, respectively. The results indicate that an intercalated or partially exfoliated nano-composite can be achieved, and the properties of the composite are significantly improved. The drug release kinetics was investigated using ofloxacin as the drug. The kinetics of the drug delivery system was systematically studied. Drug release kinetics was analyzed by plotting the cumulative release data vs. time by fitting to an exponential equation which indicates the non-Fickian type of kinetics. The drug release was investigated at different pH medium and it was found that the drug release depends upon the pH medium as well as the nature of the matrix.

The properties of barium hafnate titanate are possibly better than those of barium zirconium titanate. In general nanoscale materials possess unique electrical, magnetic, and optical properties. Barium hafnate titanate powders were prepared via sol-gel processing at different sol concentrations. X-ray diffraction and transmission electron microscopy characterization were performed. The X-ray diffraction spectra suggest that a higher calcination temperature is necessary for the powder samples prepared at lower sol concentrations to obtain a pure phase. The X-ray diffraction and transmission electron microscopy results both reveal that the average powder size decreases with the increasing of sol concentration, which may be due to the change in viscosity.