The formation of Pt8Cr in Pt 10 at.% Cr

Post deformation heat treatment of Pt 10 at.% Cr at temperatures below the recrystallisation temperature results in the formation of an ordered phase not predicted in the platinum–chromium phase diagram. Electron diffraction patterns show that the ordered structure is Pt₈Cr, which has not previously been experimentally observed. Dark field imaging shows that the ordered regions are dispersed in a deformed matrix. The kinetics of the ordering transformation are very slow.     

Crystallographic relationship of orthorhombic φ-Al5Mg11Zn4 phase to icosahedral quasicrystalline phase

The orthorhombic φ-Al₅Mg₁₁Zn₄ phase is known to be related to quasicrystalline phases, but the exact relationship has not been shown yet. In this study, the relationship of this phase to the icosahedral quasicrystalline phase is explored through analysis of the electron diffraction patterns. It is shown that icosahedral coordinations in three orientations occur in the unit cell - one with three mutually perpendicular twofold axes along 〈1 0 0〉 of the unit cell, and two with a twofold axis along [1 0 0] and a fivefold along [0 0 1]. In this, this phase is similar to aluminum and zinc based hexagonal phases which are related to quasicrystals.     

Determination of the structure of a new tetragonal U2FeAl20 phase

The atomic structure of a new ternary U₂FeAl₂₀ phase appearing in the Al-rich corner of a U–Fe–Al system was solved using electron crystallography and X-ray powder diffraction techniques (XRD). The positions of U atoms were determined from crystallographically processed high-resolution electron microscopy (HRTEM) images. These positions were used as a starting set for determining the coordinates of Fe and Al atoms by difference-Fourier synthesis technique. The U₂FeAl₂₀ phase is tetragonal and belongs to the space group. Its unit cell contains 80 Al, 4 Fe, and 8 U atoms. The lattice parameters obtained after Rietveld refinement are: a = 12.4138 Å, c = 10.3014 Å. The reliability factors characterizing the Rietveld refinement procedure are: R_p = 8.65%, R_wp = 11.2% and R_b = 5.93%.     

Nucleation and growth of the γ′(AlAg2) precipitate in Al–Ag(–Cu) alloys

Precipitation of the γ′(AlAg₂) phase was investigated in Al–Ag(–Cu) alloys using high-resolution transmission electron microscopy and scanning transmission electron microscopy. Precipitation commenced with segregation of Ag to stacking faults, followed by thickening in steps corresponding to single unit cell height ledges. In conjunction with gradual segregation of Ag and Al into ordered layers, this yielded γ′ phase platelets with a thickness of either 2 or 3 × the AlAg₂c-lattice parameter. Plates with a thickness of 2c(AlAg₂) could not achieve self-accommodation of the shape strain for transformation. Further thickening of the precipitates was slow, despite considerable Ag segregation around the precipitates. Growth by the addition of single unit cell height ledges is expected to lead to an additional shear strain energy barrier to ledge nucleation and this may contribute to a process of nucleation-limited growth.     

DO22–(Cu,Ni)3Sn intermetallic compound nanolayer formed in Cu/Sn-nanolayer/Ni structures

The present work conducts crystal characterization by High Resolution Transmission Electron Microscopy (HRTEM) on Cu/Sn-nanolayer/Ni sandwich structures associated with the use of Energy Dispersive X-ray (EDX) analysis. The results show that DO₂₂–(Cu,Ni)₃Sn intermetallic compound (IMC) ordered structure is formed in the sandwich structures at the as-electrodeposited state. The formed DO₂₂-(Cu,Ni)₃Sn IMC is a homogeneous layer with a thickness about 10 nm. The DO₂₂–(Cu,Ni)₃Sn IMC nanolayer is stable during annealing at 250 °C for 810 min. The formation and stabilization of the metastable DO₂₂–(Cu,Ni)₃Sn IMC nanolayer are attributed to the less strain energy induced by lattice mismatch between the DO₂₂ IMC and fcc Cu crystals in comparison with that between the equilibrium DO₃ IMC and fcc Cu crystals.     

Bismuth tungstate nano/microstructures: Controllable morphologies, growth mechanism and photocatalytic properties

A facile hydrothermal process was utilized to synthesize bismuth tungstate (Bi₂WO₆) hierarchical nano/microstructures, by which various morphologies could be achieved, including caddice clew-like, nest-like, flower-like and plate-like nanostructures. From the scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis, the morphologies and phases of the as-synthesized Bi₂WO₆ exhibited a strong dependence on the pH value of the precursor solutions. Moreover, the formation mechanisms of the controllable assembly of these Bi₂WO₆ nano/microstructures under different pH values were investigated. The photocatalytic performances of Bi₂WO₆ with different morphologies were also discussed, and the nest-like Bi₂WO₆ displayed the best photocatalytic activity due to the effective visible absorption and the large surface areas.     

Determination of the structure of UFe2Al10 compound

The atomic structure of a new ternary phase UFe₂Al₁₀ appearing in the U–Fe–Al system was determined using direct methods applied to X-ray powder diffraction data. High resolution electron microscopy combined with the methods of crystallographic image processing was used for the verification of the structural model. The UFe₂Al₁₀ phase is orthorhombic and belongs to Cmcm space group, its unit cell contains 40 Al, eight Fe, and four U atoms. The lattice parameters obtained after Rietveld refinement are: a=8.919 Å, b=10.208 Å, and c=9.018 Å. The reliability factors characterizing the Rietveld refinement procedure are: R_p=5.9%, R_wp=8.1%, and R_b=2.9%.     

Atomistic investigation of clustering phenomenon in the Al–Cu system: Three-dimensional phase-field crystal simulation and HRTEM/HRSTEM characterization

Early-stage clustering in quenched/aged supersaturated Al–Cu alloys is simulated and characterized at the atomic scale to study the structural and compositional evolution of clusters. A three-dimensional analysis of the nucleation and growth mechanisms of early clusters in binary alloys is built upon a phase-field crystal (PFC) methodology previously developed in two dimensions by Fallah et al. [Phys. Rev. B. 86, 134112 (2012)]. The dislocation-mediated nucleation of clusters, reproduced in three dimensions, is compared against new results of atomistic characterization using high-resolution transmission electron microscopy (HRTEM) and high-resolution scanning transmission electron microscopy (HRSTEM). Consistent with the simulation results, analysis of HRTEM micrographs reveals the association of quenched-in dislocations with the early clusters. Moreover, the PFC model and HRSTEM observations show remarkable agreement on the non-equilibrium evolution of composition within the early clusters as well as their preferred growth orientation and spherical-to-ellipsoidal morphological transition.     

Interface structure and energy in Cu–71.8 wt.% Ag

The as-cast eutectic Cu–71.8 wt.% Ag was prepared. The orientation relationship and interface structure of Cu and Ag phases were investigated using high-resolution transmission electron microscopy. The interface energies and nucleation rates in the formation of different orientation relationships were discussed. The Cu and Ag eutectic lamellae can form the cube-on-cube and hetero-twin orientation relationships and the occurrence probabilities of the two orientation relationships are approximate in the solidification of the eutectic structure. There are misfit dislocations and monolayer steps at the interface between both phases having the cube-on-cube or hetero-twin relationship. The twin fault and lattice mismatch energies at the interface result only in an insignificant effect on the formation of different orientation relationships between both phases of the eutectic laminae.     

Local structural fluctuation in Pd–Ni–P bulk metallic glasses examined using nanobeam electron diffraction

Local structural fluctuation in relation to the medium range order (MRO) in a Pd–Ni–P bulk metallic glass was examined using nanobeam electron diffraction (NBED) technique. We found diffraction spots with strong intensities in the NBED patterns taken from any observation sites in the specimen. This indicates a presence of MRO regions densely formed in the specimen. The diffraction spots in NBED were normally dispersed around positions corresponding to the first halo-diffraction ring in selected area diffraction. A low-temperature annealing led to form a nanocrystalline microstructure consisting of unidentified phosphides. In the course of annealing, the MRO structures deduced from the NBED patterns have no structural similarity to the phosphides found in the primary crystallization stage. The MRO structure changes into a similar structure with the primary crystals just before the crystallization. A discussion is made for the MRO structure and its relation to the glass stability and also to the phosphide nucleation in the primary crystallization.     

New orthorhombic phase in U-Fe-Al-Si system

A new quaternary phase with the approximate composition U-18.6 at%Fe-29.2 at%Al-32.6 at%Si was observed in U-Fe-Al-Si system. The crystal structure of this phase was investigated by electron diffraction and X-ray powder diffraction techniques. It has an orthorhombic unit cell with lattice parameters a = 12.241 Å, b = 18.362 Å and c = 4.066 Å and can be described by the Immm space group.     

Structurally modulated precipitates in a refractory Cr-V alloy

Chromium alloys are considered as high temperature structural materials. Vanadium was substitutionally alloyed into chromium to improve its room temperature ductility. Precipitates, which were indexed as C₂₀Cr₂₅V₅₅ with an orthorombic structure, form in these chromium-vanadium alloys due to the presence of carbon impurities. The distribution, morphology, and crystal defects of the precipitates were studied using electron diffraction, diffraction contrast imaging, and high resolution transmission electron microscopy. One-dimensional structural modulations were determined in these precipitates.     

Preparation and characterization of mullite whiskers from silica fume by using a low temperature molten salt method

Mullite whiskers were prepared from silica fume in molten Al₂(SO₄)₃-Na₂SO₄ mixture salts at low temperatures. The resulting mullite whiskers, as well as the nucleation and growth mechanism in the molten environment, have been investigated by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and thermogravimetric analysis (TG-DTA) techniques. XRD studies showed that the materials obtained were orthorhombic mullite. SEM, TEM and HRTEM results revealed that the mullite whiskers were single crystal fibers with diameters ranging from 30 to 150 nm and lengths of over several microns. According to thermodynamic analysis, mullite phase might be spontaneously formed in molten salts as the temperature reached the decomposition temperature of aluminum sulfate (1023 K). Moreover, the mullite crystals grew along [1 1 1] crystal plane firstly and developed into fibrous microstructure finally.     

The effect of roll gap geometry on microstructure in cold-rolled aluminum

Microstructure and texture are analyzed through the thickness of two aluminum plates cold-rolled 40% with different roll gap geometries. It is found that both texture and microstructure are strongly affected by the rolling geometry. After rolling with intermediate-size draughts a rolling-type texture is developed throughout the plate thickness. In this case, grains are subdivided by extended planar dislocation boundaries preferentially aligned at an angle of 40 ± 15° to the rolling direction. In the plate rolled with small draughts, shear texture components appear in the intermediate layers. In these layers, extended planar dislocation boundaries are frequently found to be inclined closely to the rolling direction. The subsurface and central layers of this plate exhibit microstructures similar to those in the plate rolled with intermediate draughts. It is suggested that the development of different textures and microstructures at different depths is related to the activation of different slip systems due to through-thickness strain gradients.