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This interdisciplinary work concerns misorientations across various interfaces in spark plasma–sintered (SPSed) WC–Co cemented carbides, as well as how these misorientations affect the intergranular fracture. The whole boundaries in cemented carbides were divided according to the phases on the two sides of the boundary plane, and carbide/carbide grain boundaries were further divided according to the misorientation across the boundary plane. Stereological statistics and five‐parameter analysis were comprehensively performed on the concerned boundary types. For Σ2 carbide/carbide boundaries, multiple boundary structures are observed. How Σ2 twist inhibits intergranular fracture and how such boundary structure is formed are analyzed. For random carbide/carbide boundaries, the habit planes that they are terminated by are calibrated, and their responses to intergranular fracture are examined according to their energy anisotropy. For WC/α‐cobalt and WC/β‐cobalt phase boundaries, misorientations across these boundary planes and the corresponding crack propagation routines are illustrated. On these bases, approaches to improve the fracture strength of SPSed cemented carbides are suggested. [ABSTRACT FROM AUTHOR]

Rotation axes (together with rotation angles) are often used to describe crystal orientations and misorientations, and they are also needed to characterize some properties of crystalline materials. Since experimental orientation data are subject to errors, the directions of the axes obtained from such data are also inaccurate. A natural question arises: given the resolution of input rotations, what is the average error of the rotation axes? Assuming that rotation data characterized by a rotation angle ω deviate from the actual data by error rotations with fixed angle δ but which are otherwise random, the average error of the rotation axes of the data is expressed analytically as a function of ω and δ. A scheme for using this formula in practical cases when rotation errors δ follow the von Mises–Fisher distribution is also described. Finally, the impact of crystal symmetry on the determination of the average errors of the axis directions is discussed. The presented results are important for assessing the reliability of rotation axes in studies where the directions of crystal rotations play a role, e.g. in identifying deformation slip mechanisms. [ABSTRACT FROM AUTHOR]

Manufacturing titanium alloys with simultaneous enhancement in strength and ductility has motivated extensive research into various strategies for regulating the arrangement and texture of α and β phases. The present study explores a novel α + β titanium alloy, TIMETAL 639 (Ti-639), produced by replacing a portion of vanadium in Ti-64 with molybdenum. The low diffusivity and β-stabilizing effects of molybdenum help retain bimodal characteristics within solution heat-treated Ti-639 microstructures. EBSD and TEM were used to examine β-phase evolution after thermal processing and recrystallization of new globular α grains within pre-existing colonies in a depleted bimodal microstructure. These depleted bimodal colonies in solution heat-treated Ti-639 also led to lower misorientation spreads and dislocation densities within neighboring primary α grains. Quasi-static compression along the plate normal direction demonstrated the ability of the depleted bimodal microstructure to simultaneously enhance strength and ductility in Ti-639 (~90 MPa stronger, ~6% higher failure strain) versus identically processed Ti-64. Only one solution heat-treatment step (1 h at 900 °C) is needed to achieve these properties in Ti-639, whereas comparable properties in Ti-64 required prolonged aging heat treatment (24 h at 600 °C) after the same solution heat-treatment step, making Ti-639 a viable α + β alloy candidate. [ABSTRACT FROM AUTHOR]

Geometrically necessary dislocations (GNDs) play a pivotal role in polycrystalline plastic deformation, with their characteristics notably affected by strain rate and other factors, but the underlying mechanisms are not well understood yet. We investigate GND characteristics in pure copper polycrystals subjected to tensile deformation at varying strain rates (0.001 s−1, 800 s−1, 1500 s−1, 2500 s−1). EBSD analysis reveals a non-linear increase in global GND density with the strain rate rising, and a similar trend is also observed for local GND densities near the grain boundaries and that in the grain interiors. Furthermore, GND density decreases from the grain boundaries towards the grain interiors and this decline slows down at high strain rates. The origin of these trends is revealed by the connections between the GND characteristics and the behaviors of relevant microstructural components. The increase in grain boundary misorientations at higher strain rates promotes the increase of GND density near the grain boundaries. The denser distribution of dislocation cells, observed previously at high strain rates, is presumed to increase the GND density in the grain interiors and may also contribute to the slower decline in GND density near the grain boundaries. Additionally, grain refinement by higher strain rates also promotes the increase in total GND density. Further, the non-linear variation with respect to the strain rate, as well as the saturation at high strain rates, for grain boundary misorientations and grain sizes align well with the non-linear trend of GND density, consolidating the intimate connections between the characteristics of GNDs and the behaviors of these microstructure components. [ABSTRACT FROM AUTHOR]

Sub-micro dislocation cellular structures formed during rapid solidification break the strength–ductility trade-off in laser powder bed fusion (LPBF)-processed 316L stainless steel through high-density dislocations and segregated elements or precipitates at the cellular boundaries. The high-density dislocation entangled at the cellular boundary accommodates solidification strains among the cellular structures and cooling stresses through elastoplastic deformation. Columnar grains with cellular structures typically form along the direction of thermal flux. However, the ultra-low misorientations between the adjacent cellular structures and their interactions with the cellular boundary formation remain unclear. In this study, we revealed the ultra-low misorientations between the cellular structures in LPBF-processed 316L stainless steel using conventional electron backscatter diffraction (EBSD), transmission Kikuchi diffraction (TKD), and transmission electron microscopy (TEM). The conventional EBSD and TKD analysis results could provide misorientation angles smaller than 2°, while the resolution mainly depends on the specimen quality and scanning step size, and so on. A TEM technique with higher spatial resolution provides accurate information between adjacent dislocation cells with misorientation angles smaller than 1°. This study presents evidence that the TEM method is the better and more precise analytical method for the misorientation measurement of the cellular structures and provides insights into measuring the small misorientation angles between adjacent dislocation cells and nanograins in nanostructured metals and alloys with ultrafine-grained microstructures. [ABSTRACT FROM AUTHOR]

This study investigates how deviation angles close to the [001] orientation affect the tensile properties and deformation behavior of a nickel-based single-crystal superalloy at room temperature. The research focuses on samples with deviation angles of 3°, 8°, and 13° from the [001] orientation and examines their strength and ductility. We employed scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM) to explore the deformation micro-mechanisms at varying angles. Findings reveal that strength decreases and ductility increases as the deviation angle widens within the [001] vicinity. The study emphasizes that <110> octahedral slip-driven crystal slip and rotation are crucial for understanding tensile deformation. The deformation differences in samples at varying angles are attributed to the differential engagement of mechanisms. Specifically, at lower angles, reduced ductility and increased strength are due to short lattice rotation paths and work hardening causing superlattice stacking faults (SSFs) to slip in two directions on the {111} plane within the γ′ phase. As the angles increase, the lattice rotation paths extend, and Shockley partial dislocations (a/6<112>) accumulate in γ channels. This process, involving SSFs moving in a single direction within the γ′ phase, results in higher ductility and reduced strength. [ABSTRACT FROM AUTHOR]

In this study, the effects of differences in grain size, grain boundary type and misorientation on the initiation of discontinuous precipitates are investigated for the Cu–5Ni–1.25Si alloy. Samples with different grain sizes are obtained by thermomechanical treatment, and the smaller the grain size, the higher the percentage of discontinuous precipitate at the same aging time, while there is no significant difference in the growth rate of the reaction front of discontinuous precipitates. EBSD is used to study the effect of grain boundary misorientation on discontinuous precipitates, the characteristics of discontinuous precipitates initiation on different grain boundaries are investigated by multivariate statistical analysis. It is found that discontinuous precipitates only initiate from random grain boundaries instead of coincident site lattice boundaries, where random grain boundaries with misorientation angles of 30–50° are more prone to discontinuous precipitates. And the initiation of DPs at different misorientation axes is different. There is a clear borderline for the axes such as , , and . The grain boundaries below this borderline do not initiate DP, while all grain boundaries below this angle initiate DPs. The cases for axes such as , , and are more complicated. On these misorientation axes, grain boundaries with lower or higher misorientation angles do not initiate DPs, while grain boundaries at intermediate range misorientation angles do initiate DPs.

Manufacturing titanium alloys with simultaneous enhancement in strength and ductility has motivated extensive research into various strategies for regulating the arrangement and texture of α and β phases. The present study explores a novel α + β titanium alloy, TIMETAL 639 (Ti-639), produced by replacing a portion of vanadium in Ti-64 with molybdenum. The low diffusivity and β-stabilizing effects of molybdenum help retain bimodal characteristics within solution heat-treated Ti-639 microstructures. EBSD and TEM were used to examine β-phase evolution after thermal processing and recrystallization of new globular α grains within pre-existing colonies in a depleted bimodal microstructure. These depleted bimodal colonies in solution heat-treated Ti-639 also led to lower misorientation spreads and dislocation densities within neighboring primary α grains. Quasi-static compression along the plate normal direction demonstrated the ability of the depleted bimodal microstructure to simultaneously enhance strength and ductility in Ti-639 (~90 MPa stronger, ~6% higher failure strain) versus identically processed Ti-64. Only one solution heat-treatment step (1 h at 900 °C) is needed to achieve these properties in Ti-639, whereas comparable properties in Ti-64 required prolonged aging heat treatment (24 h at 600 °C) after the same solution heat-treatment step, making Ti-639 a viable α + β alloy candidate.

In this work, an optimized method was proposed to identify the activated slip directions (i.e., gliding direction of dislocations) based on intragranular misorientation axes (IGMA) analysis only using electron backscattered diffraction (EBSD) data. By using MTEX toolbox in MATLAB software, the figures which showed the slip directions and the change of rotation angles (i.e, the grain reference orientation deviation (GROD) angles) in each grain, were plotted based on the EBSD data. By comparing the directions in which the GROD angle increases with the slip directions in the grain, the potential activated prismatic slip directions can be determined. Taking two grains in the extruded Mg–6Zn–1Y-0.5Zr alloy as examples. Two different prismatic slip directions belonging to two prismatic slip systems, [1-210] (GROD value: 0.64 → 0.75) and [-12-10] (GROD value: 0.34 → 0.74), were activated in the grain 1. Meanwhile, only one prismatic slip system, (10-10) [-12-10] (GROD value: 0.29 → 0.8), was initiated in the grain 2. Moreover, this method was further applied to determine the basal slip systems. Two basal slip systems, (0001) [-12-10] (GROD value: 2.7 → 4) and (0001) [-2110] (GROD value: 3.2 → 4.2), were activated in the selected grains, demonstrating that this method is also suitable for identifying the basal slip systems except for the prismatic systems. In summary, a novel method to determine the active slip directions in Mg alloys was successfully developed and experimentally validated in Mg alloys, which was simpler and more efficient compared to other widely utilized methods.

The multi-scale hierarchical structure of tooth enamel enables it to withstand a lifetime of damage without catastrophic failure. While many previous studies have investigated structure-function relationships in enamel, the effects of crystal misorientation on mechanical performance have not been assessed. To address this issue, in the present study, we review previously published polarization-dependent imaging contrast (PIC) maps of mouse and human enamel, and parrotfish enameloid, in which crystal orientations were measured and displayed in every 60-nm-pixel. By combining those previous results with the PIC maps of sheep enamel presented here we discovered that, in all enamel(oid)s, adjacent crystals are slightly misoriented, with misorientation angles in the 0°-30° range, and mean 2°-8°. Within this limited range, misorientation is positively correlated with literature hardness values, demonstrating an important structure-property relation, not previously identified. At greater misorientation angles 8°30°, this correlation is expected to reverse direction, but data from different non-enamel systems, with more diverse crystal misorientations, are required to determine if and where this occurs. STATEMENT OF SIGNIFICANCE: We identify a structure-function relationship in tooth enamels from different species: crystal misorientation correlates with hardness, contributing to the remarkable mechanical properties of enamel in diverse animals.

Geometrically necessary dislocations (GNDs) play a pivotal role in polycrystalline plastic deformation, with their characteristics notably affected by strain rate and other factors, but the underlying mechanisms are not well understood yet. We investigate GND characteristics in pure copper polycrystals subjected to tensile deformation at varying strain rates (0.001 s−1, 800 s−1, 1500 s−1, 2500 s−1). EBSD analysis reveals a non-linear increase in global GND density with the strain rate rising, and a similar trend is also observed for local GND densities near the grain boundaries and that in the grain interiors. Furthermore, GND density decreases from the grain boundaries towards the grain interiors and this decline slows down at high strain rates. The origin of these trends is revealed by the connections between the GND characteristics and the behaviors of relevant microstructural components. The increase in grain boundary misorientations at higher strain rates promotes the increase of GND density near the grain boundaries. The denser distribution of dislocation cells, observed previously at high strain rates, is presumed to increase the GND density in the grain interiors and may also contribute to the slower decline in GND density near the grain boundaries. Additionally, grain refinement by higher strain rates also promotes the increase in total GND density. Further, the non-linear variation with respect to the strain rate, as well as the saturation at high strain rates, for grain boundary misorientations and grain sizes align well with the non-linear trend of GND density, consolidating the intimate connections between the characteristics of GNDs and the behaviors of these microstructure components.

Sub-micro dislocation cellular structures formed during rapid solidification break the strength–ductility trade-off in laser powder bed fusion (LPBF)-processed 316L stainless steel through high-density dislocations and segregated elements or precipitates at the cellular boundaries. The high-density dislocation entangled at the cellular boundary accommodates solidification strains among the cellular structures and cooling stresses through elastoplastic deformation. Columnar grains with cellular structures typically form along the direction of thermal flux. However, the ultra-low misorientations between the adjacent cellular structures and their interactions with the cellular boundary formation remain unclear. In this study, we revealed the ultra-low misorientations between the cellular structures in LPBF-processed 316L stainless steel using conventional electron backscatter diffraction (EBSD), transmission Kikuchi diffraction (TKD), and transmission electron microscopy (TEM). The conventional EBSD and TKD analysis results could provide misorientation angles smaller than 2°, while the resolution mainly depends on the specimen quality and scanning step size, and so on. A TEM technique with higher spatial resolution provides accurate information between adjacent dislocation cells with misorientation angles smaller than 1°. This study presents evidence that the TEM method is the better and more precise analytical method for the misorientation measurement of the cellular structures and provides insights into measuring the small misorientation angles between adjacent dislocation cells and nanograins in nanostructured metals and alloys with ultrafine-grained microstructures.

This study investigates how deviation angles close to the [001] orientation affect the tensile properties and deformation behavior of a nickel-based single-crystal superalloy at room temperature. The research focuses on samples with deviation angles of 3°, 8°, and 13° from the [001] orientation and examines their strength and ductility. We employed scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM) to explore the deformation micro-mechanisms at varying angles. Findings reveal that strength decreases and ductility increases as the deviation angle widens within the [001] vicinity. The study emphasizes that octahedral slip-driven crystal slip and rotation are crucial for understanding tensile deformation. The deformation differences in samples at varying angles are attributed to the differential engagement of mechanisms. Specifically, at lower angles, reduced ductility and increased strength are due to short lattice rotation paths and work hardening causing superlattice stacking faults (SSFs) to slip in two directions on the {111} plane within the γ′ phase. As the angles increase, the lattice rotation paths extend, and Shockley partial dislocations (a/6) accumulate in γ channels. This process, involving SSFs moving in a single direction within the γ′ phase, results in higher ductility and reduced strength.

The podiform chromitite found within the Luobusha ophiolite comprises characteristic nodules and massive chromitites. However, the exact origin of these formations remains a topic of ongoing debate. In this study, the microstructures of olivine and chromite are investigated to unravel their formation processes and shed light on the associated geodynamic mechanisms. EBSD analysis provides insights into chromitite and host peridotite deformation mechanisms. Olivine grains in the host dunite and nodular chromite exhibit crystallographic preferred orientations (CPOs) with D-type fabrics, which show a girdle distribution in the [010] and [001] axes, normal to the foliation plane of the sample. The massive and disseminated chromitite displays B-type and C-type olivine fabric, with a concentration of [001] axes parallel to the lineation of the sample. Crystal plastic deformation can be observed in the Luobusha chromite grains, highlighting intercrystalline deformation processes. Small grains lacking misorientation observed in the massive chromitite are likely attributed to heterogeneous nucleation. Chromite nodules are found to be a patchwork of subgrains with various orientations and high-angle boundary misorientation. The formation of Luobusha chromitite involves deep-seated crystallization, followed by amalgamation, and subsequent deformation within the mantle peridotite. These findings distinguish Luobusha chromitite from other ophiolitic chromite deposits, offering valuable insights into the deformation history and formation processes. [ABSTRACT FROM AUTHOR]

The atomic-layer misorientation during the growth of a 5 μm thick AlN thin film on a patterned (0001) sapphire substrate was investigated by the scan rotation approach using a probe aberration-corrected scanning transmission electron microscope at a nanometer scale. Through the geometrical phase analysis of the resulting twisted atomic structure at different depths below the top surface, it is shown that over 10% of local tensile and compressive strain is balanced in a 1.6° twist of the c-planes within the first micron of AlN growth. As a consequence, the formation of threading dislocations is reduced. The in-plane twist is seen to decrease toward the layer surface down to 0.5°. Finally, growth has adopted the conventional step flow mechanism with a reduced density of emerging dislocations by the thickness of 5 μm. Our finding forecasts the possibility of understanding the relationship between atomic bilayer twist and local strain accommodation at a nanometer scale, which could provide guidance for achieving better crystal quality of AlN thin films on patterned substrates during epitaxy. [ABSTRACT FROM AUTHOR]

As part of the present project, an inquiry is being conducted into the impact of the cooling rate subsequent to extrusion on both the mechanical characteristics and microstructure of 6061 alloy extruded profiles tailored for application in the automotive industry. Water quenching, air cooling, and step-cooling (combination of air cooling and water quenching) were performed after a solution heat treatment for simulating different cooling processes on the exit of the extrusion press. Microstructure examination was performed after artificial aging for every cooling method accompanied by three-point bending and tensile testing for investigation of differences in formability characteristics in each one of the three cases. Electron fractography, texture, and grain boundary misorientation analysis consisted the main analytical techniques, allowing the correlation between grains orientation resulting from the extrusion process with cracking initiation behavior in mechanical testing and for the determination of the regions which were more prone to cracking. From the examination, the positive role of rapid cooling for improved formability was highlighted. Through the grain boundary misorientation analysis and the formation of Taylor factor maps, it was shown that crack initiation preferably took place at subsurface regions even though "roughening" of the bent surface was obvious and expected to lead to crack initiation in the more ductile samples. Considerable amounts of LAGBs (Low Angle Grain Boundaries) (14.7%) and SGBs (Subgrain Boundaries) (4.5%) were detected in the sample which was subjected to step cooling accompanied by an outer and inner surface layers (surface zone) of 200–250 μm thicknesses exhibiting different orientations. The results of this project will be used for optimization of the automotive extruded profiles production process, ensuring improved mechanical performance and resistance to premature fracture. [ABSTRACT FROM AUTHOR]

Selective Laser Melting (SLM) technology is effective for fabricating complex shape parts with superior strength and ductility. However, the high-temperature gradient and rapid solidification rate in the SLM process led to unstable material microstructure, which indicated an excellent strength and poor elongation of the SLM specimen. In order to achieve outstanding strength-plasticity matching, the influences of different solution temperatures (1000 °C, 1100 °C, and 1200 °C) on the evolution of phase and microstructure of Fe–22Cr–5Ni-0.26 N duplex stainless steel (DSS) fabricated by SLM were investigated. The results were then used to clarify the corresponding variations in mechanical properties of the specimens under tensile loading. The results revealed that the AS-SLM specimen showed high yield strength and poor elongation which was 1162.52 MPa and 4.97%. Solution treatment at 1000 °C can increase the elongation from 4.97% to 29.21% due to the two-phase structures recovered, grains refined, as well as eliminate dislocation and residual stress through recrystallization. As the temperature rose, the yield strength declined, while elongation remained almost unchanged. Except for elongation, the tensile strength, yield strength, and hardness were all higher than those of forged specimens. Therefore, solution treatment is an efficient strategy to improve the mechanical properties of the SLMFe-22Cr–5Ni-0.26 N DSS with excellent yield strength and plasticity.

The problem of obtaining priming materials from Ni–W alloys arose in connection with the development of technology for casting single-crystal turbine blades of gas turbine engines (GTE) from high-temperature alloys. This technology uses a seed method for producing single-crystal castings with a crystallographic orientation [001] using seedings from alloys of the Ni–W system with a melting point 120–140°C higher than the casting alloy. The use of such primers greatly simplifies the casting process of turbine blades with a single-crystal structure, increases its reliability both in pass-through furnaces of the PMP-2 type and in high-gradient furnaces of the UVNK-9A type. The article presents the results of the study of the influence of temperature–velocity parameters of directional crystallization, namely, the temperature gradient GZ on the structure of the obtained single-crystal seed blanks, as well as the study of effects of tungsten and carbon on the structure of single-crystal seed blanks, and makes recommendations for optimizing the technological process of single-crystal casting of Ni–W seed blanks adjusting the alloy composition for the seed blanks. [ABSTRACT FROM AUTHOR]

Al–Cu–Li bicrystals with different misorientation gradients were prepared to study the effect of misorientation and precipitates on the initial corrosion behavior of the Al–Cu–Li alloy by scanning electron microscopy (SEM), transmission electron microscopy (TEM), immersion testing, and electrochemical testing. The results show that the initial corrosions were generated on the matrix rather than on the grain boundary for the as-quenched alloy. The effect of grain boundary misorientation on the corrosion rates of the as-quenched alloy is very limited. On the other hand, for the aged alloy, the initial corrosions were generated on the grain boundaries, which suffer more severe corrosion than the matrix. Meanwhile, the corrosion of high angle grain boundary (HAGB) is more severe than that of low angle grain boundary (LAGB) for the aged alloy. These results are associated with the high number density of the continuously distributed precipitates on grain boundaries.

We investigate the effects of microfaceting on the orientation and interface structure of fcc films on fcc substrates by molecular dynamics simulations and atomic resolution electron microscopy. For (110) substrates, the simulations reveal a misorientation between film and substrate lattices that undergoes a sudden change when interfacial facets approach the "magic size", where a lattice dislocation minimizes the strain energy by compensating the misfit between film and substrate. For a large misfit, the angle of misorientation varies between zero and several degrees, depending on the size and sequence of microfacets. Experimental observations of interfaces in Ag/Ni near the Ni(110) orientation uncover the presence of magic-size {111} facets and show how microfaceting controls the partitioning of misfit dislocations. For facets smaller than the magic size, misfit may be compensated by partial rather than perfect dislocations. In vicinal {hhl} interfaces, made of {111} terraces separated by single-layer steps, a partial dislocation per terrace leads to film growth in the heterotwin orientation. This concept explains a range of previous results on interface structures in a variety of heteroepitaxial systems. [Display omitted] [ABSTRACT FROM AUTHOR]

The microstructural transformation behavior of carbide‐free bainitic steel at different strain rates is investigated using a combination of scanning electron microscopy, transmission electron microscopy, and electron backscatter diffraction. The results demonstrate that the stress–strain relationship of the steel exhibits a dependence on the strain rate, with the tensile strength increasing from 1441 MPa at a strain of 0.1 s−1 to 1537 MPa at 500 s−1, with the elongation of the sample increasing from 16.0% to 22.0% under these conditions. The increase in the strain rate raises the degree of local deformation with blocky martensite/retained austenite, exhibiting that different degrees of fragmentation and bainitic ferrite laths are observed to undergo torsional deformation. Through continuous dislocation absorption, the dislocation walls and dislocation tangles gradually develop into low‐angle subgrain boundaries, primarily located in regions with high kernel average misorientation values. After deformation at a strain rate of 0.1 s−1, the sample exhibits a Brass texture and demonstrates a combination of both Brass + Goss textures at a strain rate of 500 s−1. [ABSTRACT FROM AUTHOR]

Investigations into creep–fatigue life and the corresponding failure physical mechanism are crucial for guaranteeing the structural integrity of components. In this work, a series of strain‐controlled fatigue and creep–fatigue tests were performed at different temperatures. Then, the EBSD‐TEM combinative analysis was performed to reveal the microstructure evolution. The creep failure parameter dependence derived from standard creep experimental data and their importance in further creep–fatigue employment were discussed. Results show that strain energy density has better relevance than ductility in connecting with creep failure. The temperature‐dependent critical strain energy density and an equivalent failure strain energy density, considering geometric effect, were incorporated with the current energy‐based model, which enables creep–fatigue life scatter within a factor of 1.5. Moreover, multi‐slip activations and severe slip interactions under creep–fatigue conditions were responsible for the ultimately lifetime reductions based on microstructure observations. Highlights: Exploring the parameter dependence of creep failure.Performing creep–fatigue tests under various temperatures.Establishing a unified creep–fatigue life prediction model based on strain energy.Revealing the microscopic interactions between creep and fatigue. [ABSTRACT FROM AUTHOR]

Low-alloy 16 to 20MND5 steels are used for the production of nuclear reactor components. During manufacturing, austenitization is followed by a quench; different types of microstructures are formed during this step. Characterizing the impact of Mo and Mn and of cooling rate on these microstructures can help understand how mechanical properties will evolve during tempering and ageing. The impact of molybdenum and manganese, as well as the impact of the cooling rate, were studied on microstructures of three model alloys: FeCMo, FeCMn and FeCMoMn. This was done using continuous cooling transformation (CCT) diagrams and electron backscattering diffraction (EBSD) characterizations. FeCMoMn was found to be a good model for 16 to 20MND5 steels, based on its CCT diagram and hardness. The presence of molybdenum or manganese did not modify the misorientation angle/axis pairs of martensite. In bainitic microstructures however, the presence of Mn seemed to favor the presence of block boundaries with a misorientation about 59° [433]. On the prior austenitic grain (PAG) level, the impact of the cooling rate was rather continuous, from martensite to slowly cooled bainite, and the same regardless of the composition, with the presence of block and sub-block boundaries. The microstructure became coarser with decreasing cooling rate, with fewer crystallographic orientations per PAG. [ABSTRACT FROM AUTHOR]

Surface mechanical treatments are known to introduce deformation heterogeneity, thus entailing a combination of excellent strength and ductility in metallic metals. Accumulative skin pass rolling (ASPR) was employed to introduce heterogeneous structure in pure copper, which significantly improved yield strength and maintained high ductility. The experimental observations of the ASPR processed copper showed that surface grains possessed a much larger magnitude of misorientations and geometrically necessary dislocations (GNDs) than the centre grains. Crystal plasticity finite element modelling was utilised to provide an in-depth understanding of microstructure evolution during ASPR. It was found that the surface grains accommodated higher shear strain and had higher slip resistance than the centre grains. The multiple active slip systems in the surface grains induce the lattice rotations and then the formation of intragranular misorientations accompanied by a high density of GNDs, while the single active slip system in the centre grains can accommodate the applied material rotation without the lattice rotation.

During plastic deformation, strain weakening can be achieved, in part, via strain energy reduction associated with intragranular boundary development and grain boundary formation. Grain boundaries (in 2D) are segments between triple junctions, that connect to encircle grains; every boundary segment in the encircling loop has a high (>10°) misorientation angle. Intragranular boundaries terminate within grains or dissect grains, usually containing boundary segments with a low (<10°) misorientation angle. We analyze electron backscatter diffraction (EBSD) data from ice deformed at −30°C (Th≈ ${T}_{h}\approx $ 0.9). Misorientation and weighted Burgers vector (WBV) statistics are calculated along planar intragranular boundaries. Misorientation angles change markedly along each intragranular boundary, linking low‐ (<10°) and high‐angle (10–38°) segments that exhibit distinct misorientation axes and WBV directions. We suggest that these boundaries might be produced by the growth and intersection of individual intragranular boundary segments comprising dislocations with distinct slip systems. There is a fundamental difference between misorientation axis distributions of intragranular boundaries (misorientation axes mostly confined to ice basal plane) and grain boundaries (no preferred misorientation axis). These observations suggest during progressive subgrain rotation, intragranular boundaries remain crystallographically controlled up to large misorientation angles (>>10°). In contrast, the apparent lack of crystallographic control for grain boundaries suggests misorientation axes become randomized, likely due to the activation of additional mechanisms (such as grain boundary sliding) after grain boundary formation, linking boundary segments to encircle a grain. Our findings on ice intragranular boundary development and grain boundary formation may apply more broadly to other rock‐forming minerals (e.g., olivine, quartz). Plain Language Summary: When grains of minerals are placed under high stresses and temperatures, they develop internal (intragranular) boundaries due to the accumulation of crystal defects ("dislocations"). Over time, these boundaries introduce more local rotation ("misorientation") into the crystal structure. Eventually, the amount of rotation becomes large enough that an intragranular boundary evolves into a distinct, new grain boundary. Thus, grains become progressively subdivided during deformation. This process of subdivision allows minerals to weaken, promoting their large‐scale flow. To understand intragranular boundary development and grain boundary formation at temperatures close to the melting point, we examined the microstructure of ice samples deformed at −30°C. We found widespread variation in the crystalline structure of individual intragranular boundaries, which cannot easily be explained by previous models for boundary evolution. We propose that intragranular boundaries grow and develop by the progressive coalescence of smaller boundary sections. Furthermore, intragranular boundaries evolve via rotation around specific crystal axes. Intragranular boundaries can transform into grain boundaries, which encloses an area (grain), after rotating beyond a threshold misorientation angle. The grain boundaries are not tied to any specific rotation axis. This implies the introduction of a secondary mechanism (such as sliding along grain boundaries), which serves to disperse crystal orientations. Key Points: We propose that intragranular boundaries form via the intersection of boundary segments containing dislocations with distinct slip systemsSubgrain rotation can operate to large misorientation angles (∼38°) with rational, low‐order misorientation axes (a and m axes)Boundary misorientation axes become randomized from additional mechanisms (e.g., grain boundary sliding) following grain boundary formation [ABSTRACT FROM AUTHOR]

Two dissimilar advanced high strength steels (AHSS)—ferrite-bainite (F-B) and ferrite-martensite (F-M) steel grades were joined by gas metal arc welding (GMAW) process. Microstructure of the heat-affected zone (HAZ) after welding was critically reviewed and further correlated with the performance of the welded joint. It was observed that both the steels had softening in the HAZ, particularly in the intercritical HAZ (ICHAZ) although the reasons were found to be different. For the F-B steel grade, the extent of softening was much higher and primarily attributed to the annihilation of the dislocations (which was manifested by presence of internal strain) present in the base matrix. Besides, the volume fraction of the precipitates present in the base steel was also reduced drastically and aided in the softening process. In contrast, the F-M steel inherently contained less internal strain and the softening was predominantly due to the tempering of the martensite islands distributed in the ferrite matrix during the welding process. Thus, to extract the optimum benefits from these modern AHSSs after welding, it is important to have a thorough knowledge about the steel design philosophy (i.e., base metal chemistry and transformed microstructural products). [ABSTRACT FROM AUTHOR]

The microstructure of the tertiary oxide scale formed on the surface of low-alloy steel and local strains in three different regions were characterized by electron backscatter diffraction. Local strains of four different phase grains of hematite, magnetite, wustite, and ferrite in these three regions were systematically evaluated. A higher strength misorientation was detected around cracks of the oxide scale. On the surface of the oxide scale and the interface seam layer, Fe3O4 had a lower average local orientation difference than Fe2O3. Small spherical Fe3O4 crystal grains accumulated at the interface between the oxide layer and the steel matrix, resulting in a sharp increase in local strain, and it could be attributed to the phase transformation of magnetite during nucleation and growth processes. During high-temperature deformation, the stress released at the interface caused a different misorientation distribution at the joint seam layer. The quantification of the spatial distribution of local plastic strain in the microstructure of the tertiary oxide scale provided a good insight into the nature and distribution of crystal defects in the oxide scale, helping in controlling the formation of oxide scales during high-temperature hot rolling. [ABSTRACT FROM AUTHOR]

High-angle misorientations can significantly influence material properties. In this study, optical microscopy, Scanning Electron Microscope-Electron Backscatter Diffraction (SEM-EBSD), and Atomic Force Microscopy (AFM) have been used to investigate high-angle misorientations in quartz-bearing crustal rocks. Thin sections of high-grade quartzofeldspathic rocks were subjected to chemical mechanical polishing (CMP) with colloidal silica. In quartz, high-angle misorientations like random high angle grain boundaries (RHAGBs) and Dauphiné twin boundaries (DTBs) could be discriminated using EBSD techniques but not optical microscopy. In nanoscale AFM images, indented channels are observed along RHAGBs but not DTBs; these result from material removal during CMP, indicating lower compactness of RHAGBs compared to DTBs. Along any RHAGB, EBSD reveals different misorientations across segments between consecutive RHAGB-DTB intersections. Grains adjacent to these RHAGB segments have angles between their c-axes varying from 61-66° with parallel { 10 1 ‾ 2 } planes, and 81–84° with parallel { 11 2 ‾ 2 } planes, respectively. These symmetries represent the Japan and Sardinian twin laws of quartz, indicating that the RHAGB segments become low-energy twin boundaries, thereby reducing the overall surface energy of the aggregate. Finally, these results suggest that apart from surface topography quantification and high-resolution nanoscale imaging, AFM in conjunction with SEM-EBSD can be used for precisely locating sites for TEM study. • High-angle grain boundaries (HAGBs) in quartz aggregates vary in compactness. • Random HAGBs show indented channels in Atomic Force Microscopy (AFM) scans. • Dauphiné twin boundaries (DTBs) have greater compactness than random HAGBs. • DTB formation creates twinned random HAGB segments reducing overall surface energy. • AFM can be used for site selection before Transmission Electron Microscopy analysis. [ABSTRACT FROM AUTHOR]

As part of the present project, an inquiry is being conducted into the impact of the cooling rate subsequent to extrusion on both the mechanical characteristics and microstructure of 6061 alloy extruded profiles tailored for application in the automotive industry. Water quenching, air cooling, and step-cooling (combination of air cooling and water quenching) were performed after a solution heat treatment for simulating different cooling processes on the exit of the extrusion press. Microstructure examination was performed after artificial aging for every cooling method accompanied by three-point bending and tensile testing for investigation of differences in formability characteristics in each one of the three cases. Electron fractography, texture, and grain boundary misorientation analysis consisted the main analytical techniques, allowing the correlation between grains orientation resulting from the extrusion process with cracking initiation behavior in mechanical testing and for the determination of the regions which were more prone to cracking. From the examination, the positive role of rapid cooling for improved formability was highlighted. Through the grain boundary misorientation analysis and the formation of Taylor factor maps, it was shown that crack initiation preferably took place at subsurface regions even though “roughening” of the bent surface was obvious and expected to lead to crack initiation in the more ductile samples. Considerable amounts of LAGBs (Low Angle Grain Boundaries) (14.7%) and SGBs (Subgrain Boundaries) (4.5%) were detected in the sample which was subjected to step cooling accompanied by an outer and inner surface layers (surface zone) of 200–250 μm thicknesses exhibiting different orientations. The results of this project will be used for optimization of the automotive extruded profiles production process, ensuring improved mechanical performance and resistance to premature fracture.

Reliable information on the horizontal orientation of a seismometer is crucial to seismological research utilizing three-component seismograms. In this study, we provide misorientation angles of broadband seismometers in three permanent networks in South Korea from 2003 to 2021 by using two methods, denoted as PPCA and PminT, both utilizing P-wave polarization characteristics. Our estimates show that 36% of the sensors have been aligned within 5° from the geographic north during their operation periods, while 40% of the sensors have been rotated by more than 10° at least once. The estimates are highly consistent for both methods, with 95% of the total showing uncertainty less than 10°. Moreover, we identified a significant number of temporal changes in misorientation by taking automatic change point detection and visual inspection. The procedure described here and misorientation angles can be useful reference for seismic data preprocessing for research utilizing horizontal-component seismograms for earthquake sciences. [ABSTRACT FROM AUTHOR]

Atomistic simulations were performed to investigate the relationships among the misorientation, dislocation density, and grain boundary energy of twist and tilt bi-crystal grain boundaries. In this work, the grain boundary energies were calculated based on the embedded-atom method interatomic potential for Cu. The results show that the dislocation density of the grain boundary changes with the rotation angle, thereby affecting the grain boundary energy. Furthermore, the grain boundary energy of a grain boundary with no dislocations is greater than that of a grain boundary with dislocations, which results from the distribution of the atomic potential energy on the grain boundaries. Additionally, the grain boundary energy increases with the dislocation density of the grain boundary in the case of dislocations on the grain boundary. On this basis, a new relationship is proposed for the misorientation angle and grain boundary energy. We assume that when the driving force of dislocation nucleation breaks through the grain boundary energy barrier, the grain boundary energy declines. [ABSTRACT FROM AUTHOR]

Penetrating morphologies at the growth front of abnormally-growing Goss grains in Fe–3%Si steel was examined in view of the possibility that they are the two-dimensional section of the solid-state wetting (SSW) along the triple junction line. To obtain the statistically meaningful data, 102 penetrated grain and 204 penetrating abnormally-growing Goss grain morphologies were examined. The misorientation angles of penetrating and penetrated grains were measured by electron backscattered diffraction. Among the 102 examined penetrated grain boundaries, none has low misorientation angles less than 15°, whereas 17.2% of the 204 penetrating grain boundaries have low misorientation angles, and 23.5% of them have coincidence site lattice boundaries. Besides, boundary energies of penetrating Goss grains, which were estimated from misorientation angles of the three grains in the penetrating morphology, satisfied the energetic condition for SSW along the triple junction line. These results imply that the abnormal grain growth of Goss grains in Fe–3%Si steel occurs by the mechanism of sub-boundary enhanced SSW. [ABSTRACT FROM AUTHOR]

The aim of this paper is to evaluate an ambitious imaging experiment and to contribute to the methodology of statistical inference of the three-dimensional microstructure of polycrystalline materials. The microstructure of the considered Al-3Mg-0.2Sc alloy was investigated by three-dimensional electron backscattered diffraction (3D-EBSD), i.e., tomographic imaging with xenon plasma focused ion beam (Xe-FIB) alongside EBSD. The samples were subjected to severe plastic deformations by equal channel angular pressing (ECAP) and annealed subsequently prior to the mapping. First we compared the misorientation level needed for a reliable segmentation of grains distinguishing between conventional evaluation of two-dimensional cuts and the 3D data set. Then, using methods of descriptive spatial statistics, various morphological characteristics of a large number of grains were analyzed, as well as the crystallographic texture and the spatial distribution of grain boundaries. According to the results stated so far in the literature, an even microstructure was expected, nevertheless local inhomogeneities in grains and grain boundaries with regard to their size, texture and spatial distribution were observed and justified.

A tool to implement a length scale dependency to classical crystal plasticity simulations is presented. Classical crystal plasticity models do not include a size effect; therefore, the size of the grain does not influence the simulated deformation. Classical crystal plasticity advancements have been through the inclusion of stress or strain gradient based constitutive models to improve the simulation of length scale dependent deformation. However, this tool presents an alternative to implementing a length scale, where the influence of slip pile-up in the form of dislocations at grain boundaries as a potential to explaining the Hall-Petch effect in materials. This is achieved by calculating the slip distance in adjacent grains for each slip system, by assuming the total slip length spans the grain in the slip direction. These calculations can occur in two ways. The first is the analysis occurs at the start of the simulation, therefore, only occurs once. If this approach is used, the computational cost of this tool is minute. However, if the simulations consider large deformations, during which it is expected that the grains are going to undergo large rotations, then it would be advantageous to the have the tool recalculate the information during the analysis. Consequently, the computational cost would depend on the resolution of the modelled geometry, the number of grains, and the number of slip systems. The tool also provides a capability to develop constitutive models based on complex grain boundary features which can be implemented in classical crystal plasticity models and gradient based crystal plasticity models. The described calculation process is implemented through a Fortran subroutine, which has been designed to be easily used in crystal plasticity simulations. The presented tool also includes Python code designed to link with microstructures built using DREAM.3D to extract the required input data to the Fortran subroutine.The proposed tool is not limited to classical crystal plasticity formulations, instead the data extracted and outputted from the Fortran subroutine can be used to serve alternative purposes in both stress and strain gradient crystal plasticity models.The proposed tool can be modified to extract additional data to that presented.The slip distance in the adjacent grain, the distance from the grain boundary of the current calculation point, and the interaction between slip systems between grains can be used in any crystal plasticity constitutive models.

Competing Interests: Conflicts of interest None disclosed.