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.

Crystallographic Peculiarities of β-α Transformation in Brass Induced by Hot Extrusion

Structure-texture states in brass rods after hot extrusion and air-cooling have been investigated with the orientation microscopy (EBSD). In the examined samples, a significant concentration of β-phase with the lattice, close to bcc and fcc α-phase, has been detected. The β-phase texture consisted of the main components: two close to {110}<110> and {001}<110>. The α-phase texture consisted of the main components: close to {001}<100> and two close {110}<111>. The analysis of crystallographic relationship of the texture components of β-and α-phases demonstrates that they may all be obtained, in accordance with the orientation relations, which are intermediate between the Kurdjumov-Sachs and Nishiyama-Wasserman types It is assumed that β-α transformation began in β-phase at coincident site lattice Σ3 and Σ33a boundaries.

Spatial Resolutions of On-Axis and Off-Axis Transmission Kikuchi Diffraction Methods

Spatial resolution is one of the key factors in orientation microscopy, as it determines the accuracy of grain size investigation and phase identification. We determined the spatial resolutions of on-axis and off-axis transmission Kikuchi diffraction (TKD) methods by calculating correlation coefficients using only the effective parts of on-axis and off-axis transmission Kikuchi patterns. During the calculation, we used average filtering to evaluate the spatial resolution more accurately. The spatial resolutions of both on-axis and off-axis TKD methods were determined in the same scanning electron microscope at different accelerating voltages and specimen thicknesses. The spatial resolution of the on-axis TKD was higher than that of the off-axis TKD at the same parameters. Furthermore, with an increase in accelerating voltage or a decrease in specimen thickness, the spatial resolutions of the two configurations could be significantly improved, from tens of nanometers to below 10 nm. At a voltage of 30 kV and sample thickness of 74 nm, both on-axis and off-axis TKD methods exhibited the highest resolutions of 6.2 and 9.7 nm, respectively.

Effect of Grain Boundaries Type on Carbides Precipitates in Tempered Martensite

Different types of carbide phases and regions of their precipitation in tempered martensite of austenitic steel have been investigated with orientation microscopy (EBSD) and electron microprobe analysis. The steel structure consisted of large grains of high-temperature ferrite (~ 15%), without visible mesostructured, and martensite packages with a great number of low-angle boundaries. High-angle boundary spectrum with the most prominent coincidence site lattice (CSL) boundaries, Σ3, Σ11, Σ25b, Σ33с Σ41с, is typical for martensite. This spectrum, resulted from austenite transformation by shear mechanism according to orientation relationships (OR), intermediate between Kurdjumov-Sachs (K-S) and Nishiyama-Wassermann (N-W). In the structure two types of carbide precipitates were observed: large MC [~ NbC] along the boundaries of former austenite grains, and dispersed M23C6 [~ (W,Mo)2(Cr,Fe)21C6] predominantly along the boundaries in martensite packages. It has been shown that under martensite tempering M23C6 precipitation was mainly at high-angle intergranular boundaries. Carbide almost did not precipitate at low-angle and special CSL Σ3 boundaries. A few carbides were detected at special CSL boundaries, Σ11, Σ25b, Σ33с Σ41с.

Effect of Mesostructural Elements on Radiation-Induced Porosity in 16Cr-19Ni-2Mo-2Mn-Nb-Ti-V-P-B Austenitic Steel

Different mesostructural elements of 16Cr-19Ni-2Mo-2Mn-Nb-Ti-B austenitic steel have been examined after neutron irradiation to damage dose up to 82 dpa by scanning electron microscopy using orientation microscopy (EBSD). Radiation porosity with maximum void size up to 200 nm was observed in austenitic steel structure after neutron irradiation. Nonuniformity, related to mesostructural elements, such as general grain boundaries, special CSL boundaries Σ3 (twins), areas with high density of low-angle boundaries, is typical for radiation porosity.

Nanoscale deformation in polymers revealed by single-molecule super-resolution localization–orientation microscopy

Mechanical deformation can be detected at the nanoscale by determining fluorophore orientation in single-molecule super-resolution optical microscopy.

The Possibility of Obtaining Electrical Steel with Texture {100} <001>

We have investigated the cold rolling mesostructure and recrystallization of BCC crystals {110} <110> Fe-3%Si using a method of orientation microscopy. The 40% deformation caused shear bands with habit plane at a slope of ~20 ... 28° to the direction of rolling to form a "fishbone"-type structure. The orientation of the crystal lattice in SBs was close to {100} <001>. It can be represented as a rotation around TD close to the crystallographic direction [001] at an angle of ~ ± 37°. Such disorientation corresponds to the special disorientation CSL Σ5 (36.87о, axis [001]) between SBs and the matrix. Primary recrystallization centers in previously deformed crystal {110} <110> are formed primarily in SBs. Their orientation appears to be close to the orientation {100} <001>. It has been shown that the usage of patterns of texture formation in the shear bands of original crystallites {110} <110> allows to obtain electrical steel with a cubic texture {100} <001>.

Hot-Rolled Texture of FCC and BCC Metals

Orientation microscopy, based on electron backscattered diffraction (EBSD) has been used to study the regularities of formation of the crystallographic texture in materials with BCC and FCC lattices in the hot rolling process throughout the whole thickness of the strips. It has been established that the texture of the central layers of all samples consisted of the discrete sets of stable orientations corresponding to the cold rolling texture. In the surface layers of the samples Fe-3%Si and Al, the texture consisted of sets of discrete orientations corresponding to the shear structure. In the samples of Mo and austenitic steel, the set of discrete orientations of the surface layers matched the texture of the central layers. The difference in textures of the central and surface layers was the result of a certain stress state. The amount of friction has notably influenced the texture of the surface layer. In "hard" materials (Mo, γ-Fe), the friction was minimal, i.e. the difference in stress states of the surface and central layers was insignificant.