The Spectrum of Crystallographic Misorientations of Intercrystalline Boundaries for BCC-HCP Phase Transformation in Additively Manufactured Ti-6Al-4V

Electron backscatter diffraction is a modern experimental method for local structure and texture investigation, which makes it possible to establish the presence and types of the various boundaries between the elements of the mesostructure such as low or high angle, special and interphase boundaries. Moreover, this technique can demonstrate the migration of boundaries during structural and phase transformations. This study estimated the possible spectrum of crystallographic misorientations of intercrystalline boundaries in additively manufactured titanium alloy Ti-6Al-4V using orientation microscopy and crystallographic calculations based on Burgers orientation relationship during β→α-transformation. The study has established that the boundaries between grains of α-phase are characterized by the misorientation angles of 11±2 °, 61±5 °, 89±3 °. The majority of high-angle boundaries are characterized by misorientation angles in the range of 57-65 °. The study also ascertained that the experimental spectrum of intercrystalline boundaries in the α-phase reveals the displacive nature of β→α-transformation in titanium alloys.

Influence of Residual Stress Around Constituent Particles on Recrystallization and Grain Growth in Al-Mn-Based Alloy during Annealing

Effect of the residual stress on the recovery and recrystallization behaviors of the cold-rolled AA3003 aluminum alloy was investigated. The evolution of deformed microstructure and dislocation density characterized by TEM and Synchrotron X-ray measurements found that the change in the ratio between low angle grain boundaries (LAGBs) and high angle grain boundaries (HAGBs) during annealing is varied depending on the initial dislocation density, where the value of HAGB/LAGBs ratio is amounted to be about 0.8 at maximum. The nucleation and growth rate of the recrystallized grains are strongly dependent on the net driving pressure associated with dislocation density increased by the amount of reduction. EBSD analysis revealed that the deformed zone composed of the fine equi-axed grains with large misorientation angles would be formed in the vicinity of the constituent particles, which is consistent with the region of the large residual stress and total displacement predicted by Eshelby inhomogeneity problem under cold rolling condition.

Mechanical and Microstructural Evolution of the Mg-B Powder/Nb/Cu Cladding Using Hydrostatic Extrusion and Subsequent Drawing Process

The paper introduces the mechanical and microstructural evolution of Mg-B powders/Nb/Cu claddings fabricated using only drawing process and hydrostatic extrusion plus drawing process. We found that the Mg-B powder of the claddings during the latter process was more densified than that of the former process because of larger reduction rate in the process of hydrostatic extrusion. The claddings created by the latter process exhibited a little higher Vickers hardness values and lower grain size than those of the former process in Nb tubes. The refined microstructure of Nb tube by the latter process had higher image quality (IQ) value corresponding to lower dislocation density due to higher misorientation angles between grains than that of the former process, thereby demonstrating the broadly distributed (110) fiber texture.

Methodology for the Identification of Nucleation Sites in Aluminum Alloy by Use of Misorientatation Mapping

The fabrication of semi-finished hot and cold rolled sheets includes a complex evolution of both microstructure and texture to meet the demanded mechanical properties and suitable formability characteristics. The desired mechanical properties along with the optimum grain size can be obtained through the control of both recovery and recrystallization processes. This work examines the effect of recovery and recrystallization on the resulting crystallographic texture and on the local plastic deformation. A processing approach for EBSD-KAM (Electron Back Scatter Diffraction—Kernel average misorientation) evaluation is suggested with the purpose of effectively evaluating all the possible misorientation angles in-between the grains and of observing the recovery phenomenon from a different point of view. The results showed that although texture components did not alternate significantly during recovery, the fraction of sub-grain boundaries was increased indicating the completion of recovery at the selected temperature exhibited a maximum value of 90%. The initiation of recrystallization was illustrated by a different aspect, underlying newly formed grains and points which exhibited high misorientation angle, critical for the evolution of the recrystallization process and texture evolution.

Базовые элементы структуры границ зерен наклона. Часть 2. Оси разориентации [110] и [111]-=SUP=-*-=/SUP=-

The computer simulation methods have been applied to calculate structure and energy of symmetric tilt grain boundaries (GB) with the misorientation axes [110] and [111]. The calculations have been carried out with the use of the structural-vacancy model. The study of the atomic structure has been carried out within the entire range of misorientation angles. The reverse density of coincidence sites in special grain boundaries has amounted Σ≤57. The calculations have been carried out with the use of the Morse pair potential and the Cleri-Rosato many-body potential. When calculated with different potentials, the dependence of GB energy on the misorientation angle has a similar form, and the atomic structure completely coincides. It has been shown that the structure of any GB with the misorientation axes [110] and [111] may be represented by a limited number of basic structural units. All found basic structural units defined as units of A, B, C and D types are based on the structures of special grain boundaries. Such special GBs shall be Σ3(111), Σ3(112), Σ11(113) and Σ9(114) for GBs with the misorientation axis [110], and as regarding GBs with the misorientation axis [111], such special GBs shall be Σ3(112), Σ7(123) and Σ13(134). Ranges of angles within which certain basic structural units are found have been defined.

THE STRUCTURE FORMATION OF RAPIDLY SOLIDIFIED FOIL OF THE EUTECTIC ALLOY SN-8,8 WT. % ZN

Представлены результаты исследования микроструктуры быстрозатвердевшей фольги эвтектического сплава Sn - 8,8 мас.% Zn поверхностей A и B, определены параметры микроструктуры. Проведено исследование текстуры выделений твёрдых растворов олова и цинка в фольге, представлены полюсные плотности дифракционных линий данных фаз. Изучено влияние сверхбыстрого охлаждения на распределение углов разориентации соседних и случайно выбранных зёрен для поверхностных слоёв фольги, контактирующих с подложкой () и атмосферой () соответственно. The results are presenred of a study of the microstructure of rapidly solidified foil of the eutectic alloy Sn - 8,8 wt.% Zn A and B surfaces, microstructure parameters are determined. The texture of the precipitates of tin and zinc solid solutions in the foil was studied, and the pole densities of the diffraction lines of these phases are presented. The effect is studied of ultrafast cooling on the distribution of misorientation angles of neighboring and randomly selected grains for surface foil layers in contact with surfaces A and B .

The Significance of Coherent Transformation on Grain Refinement and Consequent Enhancement in Toughness

Coherent transformation is considered to be an effective approach to refine the microstructure and enhance toughness of structural steels. However, there are gaps in the knowledge on the key aspects of microstructure that govern toughness. In this regard, a low alloyed experimental steel with lean chemistry was subjected to a simple heat treatment involving austenitization at different temperatures, followed by quenching and tempering to obtain bainitic microstructures with different boundary composition. The microstructure of the four experimental steels was characterized by electron backscattered diffraction and mechanical properties were determined. The study indicated that the density of high angle grain boundaries does not adequately reflect the change of ductile-to-brittle transition temperatures (DBTT) of the experimental steels. Thus, we propose here a new mechanism on reducing DBTT from the perspective of misorientation of boundary, which takes into consideration these aspects in defining DBTT. One is inhibition effect on cleavage fracture by boundaries with high {100}-plane misorientation angles, and the other is ductility improvement by boundaries with high {110}-plane misorientation angles. Furthermore, the contribution of prior austenite grain boundary, packet boundary, block boundary, and sub-block boundary on toughness is also analyzed.

Orientation Ordering and Chiral Superstructures in Fullerene Monolayer on Cd (0001)

The structure of C60 thin films grown on Cd (0001) surface has been investigated from submonolayer to second monolayer regimes with a low-temperature scanning tunneling microscopy (STM). There are different C60 domains with various misorientation angles relative to the lattice directions of Cd (0001). In the (2√3 × 2√3) R30° domain, orientational disorder of the individual C60 molecules with either pentagon, hexagon, or 6:6 bond facing up has been observed. However, orientation ordering appeared in the R26° domain such that all the C60 molecules adopt the same orientation with the 6:6 bond facing up. In particular, complex chiral motifs composed of seven C60 molecules with clockwise or anticlockwise handedness have been observed in the R4° and R8° domains, respectively. Scanning tunneling spectroscopy (STS) measurements reveal a reduced HOMO–LOMO gap of 2.1 eV for the C60 molecules adsorbed on Cd (0001) due to the substrate screening and charge transfer from Cd to C60 molecules.

Modern Techniques for Automated Acquiring and Processing Data of Diffraction Electron Microscopy for Nano-Materials and Single-Crystals

Progress in modern science and technology is impossible without the use of new materials, which include nanoparticles and single crystals. Existing approaches in the field of computer vision are difficult to apply to the processing of diffraction patterns, which contain information about the parameters of the fine structure of nanostructured and single-crystal materials. The aim of the work was to develop modern computer-aided techniques that, interacting with the software of the electron microscope, automatically receive and process the information contained in electron diffraction patterns. Replacing the diffraction pattern obtained by a transmission electron microscope with a three-dimensional relief makes it possible to reduce the problem to the solution of the optimization problem. This approach allows not only automating the process of scientific research, but also significantly reduces the time for obtaining the result and increases its accuracy. The application of the proposed approach is demonstrated in measuring the misorientation angles of large single-crystal tungsten ingots, which are obtained by the plasma-induction growing technology.