Atom vacancies at a screw dislocation core in SrTiO3

A screw dislocation in strontium titanate has been studied taking benefit of negative spherical aberration-imaging in a spherical aberration-corrected transmission electron microscope. The core structure of the dislocation is atomically resolved with respect to both cation and oxygen columns by the inclusion of the central core area. The dislocation core is characterized by a helical distortion of the lattice planes, which leads, in particular, to azimuthally elongated image dots associated with individual atomic columns close to the core centre. The atomic coordination in the dislocation core is identified and a high density of atom vacancies is revealed for a Ti–O column at the core.     

Cooling-rate-dependent microstructure and mechanical properties of a CuZrAlAg alloy

A Cu₃₆Zr₄₈Al₈Ag₈ alloy rod with a diameter of 10 mm was fabricated using a copper-mould suction casting method. Structural characterization revealed that the rod has different microstructures along the casting direction, including a complete amorphous structure and an amorphous/crystalline composite structure with different amount of B2 CuZr phase. Nanoindentation tests showed that the hardness and the elastic modulus of the crystalline phase are lower than those of the amorphous matrix. The hardness and the elastic modulus of the amorphous matrix decrease with decreasing crystalline proportion of the alloy, while the Vickers hardness of the alloy increases with a reduction in the crystalline proportion.     

Thermal stability of nanocrystalline fcc and hcp Ni(Si) synthesized by mechanical alloying of Ni90Si10

The thermal stability of nanocrystalline fcc and hcp Ni(Si), obtained by mechanical alloying of Ni₉₀Si₁₀, has been studied. The allotropic transformation from fcc to hcp Ni(Si) is accompanied by a volume expansion of 8.6% and is observed when fcc Ni(Si) reaches a critical crystallite size of 10nm. The hcp phase transforms to stable fcc Ni(Si) at 573K. It has been identified that the lattice distortion in nanometre-sized crystallites from the equilibrium configuration and the decrease in the interfacial energy with grain refinement act as self obstacles in controlling the grain growth of nanocrystalline materials.     

3D shape and orientation of nanoscale Pb inclusions at grain boundaries in Al observed by TEM and STEM tomography

We have combined high-angle annular dark field/scanning transmission electron microscopy (HAADF-STEM) tomography with bright field (BF)-TEM tomography to characterize small inclusions of Pb at a grain boundary in Al. It was found that the shape of the grain boundary inclusions is more complex than previously thought. By using moiré fringes observed at some orientations of the specimen in a BF-TEM tomographic tilt series, we were able to determine the orientation of each grain, the axis and angle of misorientation of the grain boundary, and the facet planes of the grain boundary inclusions. The 3D shape of the inclusions was determined by merging this information with the HAADF-STEM tomography.     

Formation of plate-shaped Guinier–Preston zones during natural aging of an Al–Zn–Mg–Cu–Zr Alloy

Plate-shaped Guinier–Preston (G–P) zone formation in an Al–Zn–Mg–Cu–Zr alloy has been studied using transmission electron microscopy. The results provide, for the first time, direct evidence showing nucleation and growth of plate-shaped coherent G–P zones during natural aging.     

Annealing of europium-implanted silicon by nanosecond ion-beam pulses

Ion implantation into Si(100) was made with Eu⁺ ions at 25 keV to doses of 1.2 x 10¹⁵ and 1.2 x 10¹⁶ ions cm^-2     

Microstructural development during transient directional solidification of a hypomonotectic Al–In alloy

Upward directional non-steady-state solidification experiments have been performed on a hypomonotectic Al–5.5?wt%In alloy. The alloy developed cellular as-solidified microstructure for tip growth rates, V _L, higher than 0.95?mm/s. The casting regions associated with V _L?<?0.95?mm/s were shown to be characterized by a microstructure formed by In droplets disseminated in the Al matrix. Tip growth rate and microstructural features, such as cell spacing and interphase spacing, have been experimentally determined. The experimental cell spacings have been compared with theoretical predictions furnished by the Hunt–Lu model. It was found that the experimental scatter lies below the minimum range of values theoretically predicted. Moreover, the experimental cell spacing evolution with V _L is characterized by a ?1.1 power law. The droplets’ interphase spacing, λ, is related to the growth rate by the Jackson–Hunt relationship (λ ² V _L?=?constant).     

Production of recrystallized nano-grains in a fine-grained Cu–Zn alloy

A fine-grained Cu–30%Zn alloy sheet was rolled at 77 K to induce ultrafine mechanical twins. Subsequent annealing of the rolled alloy at temperatures up to 543 K led to the uniform appearance of recrystallized ultrafine grains (UFGs), which contained numerous annealing twins. Average grain sizes of 150 ～ 300 nm were produced in this way. The formation of such UFGs during annealing is attributed to the high nucleus density associated with the fine initial grain size as well as to the high densities of mechanical twins and dislocations produced by cryorolling. The high driving force for recrystallization enabled the use of relatively low annealing temperatures, which limited the subsequent grain growth.     

Effect of thermoelectric magnetic force on the array of dendrites during directional solidification of Al–Cu alloys in a high magnetic field

By eliminating the effect of the magnetic moment arising from the magnetic crystalline anisotropy, the effect of the thermoelectric magnetic force on the array of dendrites during directional solidification of Al–35?wt%Cu and Al-40?wt%Cu alloys in a high magnetic field has been investigated experimentally. The results indicate that the dendrite array is essentially destroyed, a result that could have general significance for understanding the processes involved in the solidification of alloys in a magnetic field.