Crystallographic Misorientation Research Articles

Optimizing Rolling Strategies for API 5L X80 Steel Heavy Plates Produced by Thermomechanical Processing in a Reversible Single-Stand Mill

This study focuses on advancing the production of predominantly bainitic heavy plates to meet the API 5L X80 standard. The investigation involves a thorough evaluation of the influence of rolling parameters and austenite conditioning on both microstructural characteristics and mechanical properties. Accurate specifications for chemical composition, processing temperatures, and mean deformations were established using mathematical models and bibliographical references. Four rolling conditions were performed in a reversible single-stand mill, allowing for comprehensive comparison and critical analysis. Microstructural and mechanical characterizations were performed utilizing several techniques, including optical microscopy (OM), scanning electron microscopy (SEM), tensile tests, Charpy impact tests, and hardness tests to ensure adherence to API 5L standards. Additionally, the SEM-EBSD (electron backscattered diffraction) technique was employed for a complementary analysis. The EBSD analysis included crystallographic misorientation maps, mean kernel misorientation parameters (ϑ), low- and high-angle grains boundaries, mean equivalent diameter, and evaluation of the contribution of different strengthening mechanisms to yield strength. Results underscored the significant influence of austenite conditioning on both microstructure and mechanical properties. Considering the specificities of a reversible single-stand mill, it was concluded that, unlike the classic approach for ferritic or ferritic–pearlitic HSLA (high-strength low-alloy steel), when a product with a predominantly bainitic microstructure is required, the accumulated deformation in the austenite during the finishing rolling stage, as well as its temperature, must be meticulously controlled. It was shown that the greater the deformation and the lower the temperature, the more favorable the scenario for the undesired polygonal ferrite formation, which will deteriorate the material’s performance. Furthermore, an optimized production route was identified and adapted to the specificities of the employed rolling mill. The presented data have great importance for researchers, manufacturers, and users of API 5L X80 heavy plates.

Molecular dynamics simulations of nanoparticle sintering in additive nanomanufacturing: The role of particle size, misorientation angle, material type, and temperature

Additive nanomanufacturing, where nanoparticles (NPs) are generated via laser material ablation and sintered via laser, permits the fabrication of novel electronic devices with adequate flexibility, such as tunable material composition, adjustable sintered state, and a wide selection of substrates—including biodegradable ones—to name a few. The laser energy input often needs to be carefully balanced between achieving adequate sintering and avoiding substrate damage. The sintered state of NPs, a key influencing factor of the resistivity of electronic circuits, depends not only on temperature (the result of laser energy input), but also on NPs size, size ratio, and crystallographic misorientation. While the minuteness of NPs and the transient nature of their sintering (typically within a nanosecond) make direct experimental evaluation of such parameters challenging, the length and time scales are uniquely suitable for molecular dynamic (MD) studies. This study utilizes MD to investigate the sintering characteristics of silver and copper NP doublets at different temperatures and examines the effects of NP size, size ratios, misorientation angle (including both tilt and twist), and material type. A mathematical framework to describe the characteristic sintering time, i.e., time needed for a NP doublet to achieve a given normalized neck size, was proposed based on MD results.

Study on subgrain boundaries in cast monocrystalline silicon

Cast monocrystalline silicon (mono-Si), also known as quasi-mono-Si, has been recognized for its potential as a high-performance crystalline silicon material due to its low manufacturing costs and high crystal quality. This study investigated the occurrence of high-density dislocation loops in cast mono-Si, which exhibited grid-like propagation caused mostly by subgrain boundaries. The study looked at the fundamental properties of these subgrain boundaries as well as the mechanisms that allow them to propagate in a grid-like pattern within cast mono-Si. Observations revealed differences in the crystallographic misorientation of subgrain boundaries across the ingot, ranging from 1 to 3°. Electron Beam Induced Current (EBIC) tests revealed strong recombination activity at these boundaries under typical conditions. As the temperature gradually decreases from 300 K to 80 K during EBIC testing, subgrain boundaries with shallower energy states emerge, which become more apparent in photoluminescence (PL) tests conducted on Si wafers cut from different heights of the ingot.

Development of crystallographic misorientation in laser powder bed fusion 316L stainless steel

This study examines the development of crystallographic misorientation and its relations to the solidification microstructure in Laser Powder Bed Fusion (LPBF) alloys. We performed a single laser track experiment on an SS316L single-crystal substrate to characterize the correlation between solidification features and misorientation evolution within a single LPBF melt pool and found that the sources of misorientations inside the melt pool can be attributed to both rapid solidification (misorientation aligning precisely with the cell walls & colony boundaries) and residual stress-induced plastic deformation (misorientation independent of solidification morphology), while the residual stress-induced plastic deformation acts as the sole mechanism to extend this misorientation outside of the melt pool boundary. The misorientation development both inside and outside of the melt pool always occurs through a crystal rotation around one of the {111} axes without any obvious correlation with the sample orientations. Additionally, we conducted a comprehensive literature overview of mechanisms in the solidification process and critically assessed the current understanding of misorientation formation and the causes of the loss of epitaxial grain growth.

Electron backscatter diffraction analysis combined with NanoSIMS U–Pb isotope data reveal intra-grain plastic deformation in zircon and its effects on U–Pb age: examples from Himalayan eclogites, Pakistan

Abstract. Zircon grains preserve records of crystallization, growth, and/or deformation that can be envisaged from their internal structures and through the U–Pb isotope analysis. Electron backscatter diffraction (EBSD) is a non-destructive method for visualizing undeformed domains to differentiate them from those that are plastically deformed. In this study, we report EBSD analyses conducted on zircon grains, in thin sections with available textural information, from Himalayan eclogites. The studied eclogite samples show no petrographic evidence of shearing or mylonitization. However, several zircon grains preserve plastically deformed domains. These deformed domains display several degrees of misorientation relative to the undeformed domain and yielded geologically reset ages when analysed for U–Pb isotope ratios using nanoscale secondary ion mass spectrometry (NanoSIMS), in contrast to most undeformed domains which retained the protolith age. The degree of resetting is positively correlated with the extent of misorientation. These pieces of evidence indicate that plastic deformation in zircon grains, equilibrated at higher pressure–temperature conditions, affected the primary geochemical and geochronological records. Based on these observations, we assume that not only regional shearing/mylonitization in metamorphic rocks affects the geochemical records, but also that zircon grains in apparently unsheared high-grade metamorphic rocks behave plastically. The micro-scale intra-grain plastically deformed domains can easily be identified through EBSD analysis in the form of crystallographic misorientations. To extract meaningful geochronological results, it is necessary to identify undisturbed domains in zircon grains before applying any destructive analytical method.

The anisotropic grain size effect on the mechanical response of polycrystals: The role of columnar grain morphology in additively manufactured metals

Additively manufactured (AM) metals exhibit highly complex microstructures, particularly in terms of grain morphology which typically features heterogeneous grain size distribution, irregular and anisotropic grain shapes, and the so-called columnar grains. The conventional morphological descriptors based on grain shape idealization are generally inadequate for representing complex and anisotropic grain morphology of AM microstructures. The primary aspect of microstructural grain morphology is the state of grain boundary spacing or grain size whose effect on the mechanical response is known to be crucial. In this paper, we formally introduce the notion of axial grain size from which we derive mean axial grain size, effective grain size, and grain size anisotropy as robust morphological descriptors capable of effectively representing highly complex grain morphologies. We instantiated a discrete sample of polycrystalline aggregate as a representative volume element (RVE) featuring random crystallographic orientation and misorientation distributions. However, the instantiated RVE incorporates the typical morphological features of AM microstructures including distinctive grain size heterogeneity and anisotropic grain size owing to its pronounced columnar grain morphology. We ensured that any anisotropy observed in the macroscopic mechanical response of the instantiated sample primarily originates from its underlying anisotropic grain size. The RVE was then employed for mesoscale full-field crystal plasticity simulations corresponding to uniaxial tensile deformation along various axes via a spectral solver and a physics-based crystal plasticity constitutive model which was developed, calibrated, and validated in earlier studies. Through the numerical analyses, we isolated the contribution of anisotropic grain size to the anisotropy in the mechanical response of polycrystalline aggregates, particularly those with the characteristic complex grain morphology of AM metals. This contribution can be described by an inverse square relation.

Exceptional thermal stability of additively manufactured CoCrFeMnNi high-entropy alloy with cellular dislocation structures

CoCrFeMnNi high-entropy alloy (HEA) was additively manufactured (AM) by laser powder-bed fusion (L-PBF). The AM CoCrFeMnNi has prominent cellular dislocation structures with a small number of Mn-rich oxides. The thermal stability of the AM CoCrFeMnNi was investigated by isochronal annealing treatment at various temperatures from 400 to 1300 °C for 1 h. Microstructural analysis shows slow dislocation recovery, retarded recrystallization process, and precipitation of additional Cr-Mn based oxides during thermal annealing, resulting in exceptional thermal stability and retained high hardness at elevated temperatures. By thermodynamic calculations, a low stored energy of 1.31 MJ/m3 and a high activation energy of 353 kJ/mol for recrystallization were estimated for the AM CoCrFeMnNi. The exceptional thermal stability of the AM CoCrFeMnNi HEA is mechanistically attributed to the low crystallographic misorientations across the dislocation cell walls, sluggish atomic diffusion, and the pinning effects of the oxide nanoprecipitates.

Mechanism and age of gold remobilization in orogenic gold deposit from primary laminated ore to the high-grade ore: A case study from Cenozoic Bangbu gold deposit, Tethyan Himalaya

The formation of high-grade gold ore has always been attractive, mostly located in Precambrian gold deposits with various mechanisms. Yet, in the orogenic Bangbu gold deposit, Tibet, we discovered that the coupled dissolution-reprecipitation (CDR) process and low melting point chalcophile elements (LMCE) -related melting are responsible for the formation of high-grade ore at ca. 38 Ma constrained by in-situ U-Th-Pb dating of hydrothermal monazite. Three generations of pyrite have been recognized, metamorphic barren pyrite (Py I) in the host schist, hydrothermal pyrite (Py II) in the preceding primary laminated ore with an Au grade of ∼8 g/t, and the hydrothermal coarse pyrite (Py III) in later massive ore with a grade of up to 29 g/t. In the primary laminated ore, the Py II in the sulfide ribbons is intergrown with native gold and colloform quartz and carries abundant trace element contents, such as Au, As, Cu, Pb, Zn, Te, Se, and Bi. These suggest that the rapid precipitation and local supersaturation occurred during the episodic crack-seal process. In the later high-grade massive ore, Py III exhibits distinct zonation, ranging from Py III-1 in the core to Py III-3 in the rim. The Py III-1, porous and rich in inclusions, has sharp boundaries and successive lattice orientation with the mantle Py III-2 suggesting a CDR process. Higher Au and As in Py III-2 than the Py III-1, and the close affinity between visible gold and LMCE melt inclusions at the boundary suggest that gold was remobilized and facilitated by the LMCE during the CDR process. The electron backscatter diffraction (EBSD) mapping result shows little crystallographic misorientations of Py III, excluding the deformation process that has significantly contributed to the remobilization of gold. The decrease of the δ34S ratio of pyrite between Py II (δ34S = 2.0‰ to 4.3‰, mean 3.4‰) and Py III (δ34S = −2.5‰ to 3.8‰, mean −0.2‰) most likely reveals a more oxidized condition in the open space which may trigger the CDR process and gold remobilization of the pyrite in the primary ore. Within the zonation of Py III, an increasing trend of the δ34S ratio represent the evolution of the redox state of fluids towards relatively reducing conditions during the healing of quartz veins. The newly obtained ca. 38 Ma age is comparable to regional amphibolite- to granulite-facies metamorphism during the continental subduction, which was considered to trigger the modification of primary gold orebody to form high-grade ore.

A novel microwall sliding test uncovering the origin of grain refined tribolayers

The tribology induced microstructure determines the tribological properties of metals. Yet the complex interaction of multiple microcontacts makes it impossible to decouple the fundamental plastic mechanisms. Single nano-/microasperity sliding tests allow to separate the microcontacts and to study the origins of plastic evolution during the initial stages of wear. However, the fundamental formation mechanisms of the sliding induced grain refinement are still largely unknown. In this work, we pre-remove material around the wear track and produce microwalls, which simplify the stress state and allow to directly inspect the contact zone. After sliding on the microwalls, a misorientation jump forms in the crystal orientation below the wear track. The crystallographic misorientation reaches 30° in some configurations, resulting in the formation of large angle grain boundaries. The misorientation jump formation depends on the grain orientation, wear direction and on twin boundaries in its path. We unravel the grain formation mechanism via slip-step and dislocation analysis and address dislocation arrangements at the grain boundary. This novel microwall sliding test has a potential to better understand the origins of microstructure modification in metals during the run-in stage of wear.

(Invited) Electron Channeling Contrast Imaging for Rapid Characterization of Compound Semiconductors

As compound semiconductor devices become more advanced, their ultimate performance becomes increasingly dependent on nano to micro scale structural defects in their constituent materials. These defects, such as dislocations, stacking faults, and anti-phase boundaries often act as recombination centers in devices, limiting efficiency. Characterization of these defects – their type (such as edge vs. screw vs. mixed dislocations), their relative densities, how they interact with other defects, what growth conditions are more or less likely to propagate them, how they relate to device efficiencies and performance, etc. – is vital to mitigate their negative effects and even sometimes exploit their potential benefits depending on the desired application. In this contribution, we will discuss the use of electron channeling contrast imaging (ECCI) as an ideal characterization method for compound semiconductors and devices as well as some recent applications which include ECCI characterization in tandem with other characterization methods for a broader material understanding.Transmission electron microscopy (TEM) is a widely used technique for characterizing extended defects and local crystal orientation. However, TEM analysis usually entails thinning a sample via focused ion beam milling or chemical/mechanical polishing to around 50-100 nm, which is time consuming and only allows a relatively small area of the sample to be characterized. These drawbacks can cause bottlenecks in research progress and even render TEM impractical for certain applications. ECCI performed in a scanning electron microscope (SEM) can bypass these issues as it requires little to no sample preparation. This means ECCI can easily characterize over large areas in a fraction of the time as TEM analysis. [1-3] These benefits mean that ECCI gives more accurate analysis by not missing larger trends that can be missed with the small samples in TEM as well as by not introducing artifacts from the sample preparation.Here we highlight applications of ECCI for characterization of two very different compound semiconductors of growing importance -- Cd3As2 and GaN. Firstly, we consider Cd3As2 thin films of use as topological quantum materials, where the Cd3As2 can be either a compound semiconductor or topological Dirac semimetal, depending on the structural phase or mode of use. The ECCI of MOCVD-grown Cd3As2 shown in this work finds that the developmental thin films are not completely single crystalline. [4] Moreover, two different spatial scales of domain formation are seen. At lower magnification, we see roughly circular-shaped larger domains that are ~ 2-5 mm in diameter. Some of these domains are more prominently defined and feature single dark spots at their center, which at first suggests threading dislocations, but turns out to be occasional defect-pits formed in concert with numerous, indistinct threads. At higher magnification, we see much smaller dot-like or speck-like domains that are ~ 100 nm or less in diameter. The wide-area electron channeling patterns used to orient the sample for the ECCI imaging were visible, but rather indistinctly resolved, which is consistent with small crystallographic misorientations of the ensemble of domains composing the film. Secondly, we consider bulk GaN wafers entering use in a wide variety of functional applications, including GaN high-voltage diodes for power electronics. We will show novel “star” defects appearing in the GaN substrates when characterized by both ECCI and high-resolution electron backscattered diffraction (EBSD). [5] Through a more complete structural understanding of these star defects, we seek to improve understanding of the impact of these defects on device performance, which may in turn facilitate development of strategies for their mitigation or removal.Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

Topological aspects of mean-field crystallographically resolved models

It is well-known that the crystallographic texture of a polycrystalline aggregate can be represented by the Orientation Distribution Function (ODF). A similar statistical approach can be extended to other microstructural state variables that are of relevance in the context of obtaining microstructurally based and quantitatively accurate structure-properties relations. In principle such statistical representations are of a non-topological nature, in contrast to an RVE (Representative Volume Element) description of the microstructure. However, by including additional variables to the statistical descriptor specific features of the topology may be taken into account. In this paper the example will be shown on how the plastic anisotropy simulation of a conventional deep drawing grade of Interstitial Free (IF) steel can be improved by considering the crystallographic misorientation of pairs of neighboring crystals, which represent the basic structural units of the 2-point mean field ALAMEL crystal plasticity model. In another example it will be shown how the recrystallization texture of the same deep drawing IF steel can be modelled with improved accuracy if the Strain Induced Boundary Mechanism (SIBM) is taken into account whereby a crystal orientation of low stored energy grows into a neighboring orientation of high stored energy.

Microstructural and textural modification of columnar calcite under increasing shear strain (Evia Island, Greece)

We studied the microstructural and textural modification of columnar calcite naturally deformed at increasing shear strain. The studied marbles were sampled from different structural levels of the Basal Unit of the Cycladic Massif on Evia Island, Greece. The marbles have experienced high pressure metamorphism at peak temperatures around 350 °C. The long axes of the columnar calcite grains and their c-axes were originally oriented normal to the foliation and were subsequently rotated during exhumation. The obliquity of the long axes of relict calcite grains with respect to the foliation was used to infer shear strain. Electron backscatter diffraction (EBSD) analysis was used to characterize the marble microstructure as well as the crystallographic preferred orientations (CPO) and misorientations in calcite. Recrystallization of calcite was active from very low shear strains (0.1) and mylonitization (∼60% area fraction of recrystallized grains) took place at shear strains >∼4. Subgrain rotation was the dominant recrystallization mechanism in calcite in all samples. Differential stress and strain rate did not show any systematic variation with increasing shear strain. A shear strain of up to ∼4 was not enough to produce a strong CPO in calcite.

Thermomechanical properties of cold-sprayed copper coatings from differently fabricated powders

Cold spraying is a material coating deposition process that accelerates powders to high velocities, thereby causing them to undergo intensive plastic deformation upon impact in solid states at temperatures far below their melting point. The critical powder velocity is the most influential factor determining the bonding strength of cold spray coatings and strongly depends on the thermomechanical interactions between the sprayed powder and the substrate material. In this study, three commercially available Cu feedstocks fabricated through electrolysis (EP), gas-assisted water atomization (WA), and inert gas atomization (GA) were characterized and used to produce cold spray coatings. The kernel average misorientation (KAM) data from electron backscatter diffraction (EBSD) analysis were used to determine the plastic strain distribution of the Cu powders and coatings through local crystallographic misorientation. The percentages of the local misorientation within grains with angles higher than 1.5° in the EP (3.0%) and GA (2.8%) powders were similar, whereas that in the WA powder (0.6%) was the smallest. According to the EBSD data, more dynamic recrystallization and, in turn, more plastic strain release occurred in the as-sprayed EP and GA coatings than in the WA coating. The tendency of recrystallization of the twin grains in the as-sprayed GA coating and its influence on the ductility of the coating are discussed in relation to the GA powder's bonding mechanisms. The static recrystallization in the postannealing treatment (at 190 °C for 1 h) of the EP and GA coatings being more prominent than in that of the WA coating supports differences in dynamic recrystallization among the cold-sprayed coatings determined through EBSD analysis. The thermal conductivity of cold-sprayed Cu coatings is influenced by recrystallization and strain release.

Black Drum Fish Teeth: Built for Crushing Mollusk Shells

With an exclusive diet of hard-shelled mollusks, the black drum fish (Pogonias cromis) exhibits one of the highest bite forces among extant animals. Here we present a systematic microstructural, chemical, crystallographic, and mechanical analysis of the black drum teeth to understand the structural basis for achieving the molluscivorous requirements. At the material level, the outermost enameloid shows higher modulus (Er = 126.9 ± 16.3 GPa, H = 5.0 ± 1.4 GPa) than other reported fish teeth, which is attributed to the stiffening effect of Zn and F doping in apatite crystals and the preferential co-alignment of crystallographic c-axes and enameloid rods along the biting direction. The high fracture toughness (Kc = 1.12 MPa⋅m1/2) of the outer enameloid also promotes local yielding instead of fracture during crushing contact with mollusk shells. At the individual-tooth scale, the molar-like teeth, high density of dentin tubules, enlarged pulp chamber, and specialized dentin-bone connection, all contribute to the functional requirements, including confinement of contact compressive stress in the stiff enameloid, enhanced energy absorption in the compliant dentin, and controlled failure of tooth-bone composite under excessive loads. These results show that the multi-scale structures of black drum teeth are adapted to feed on hard-shelled mollusks. Statement of significanceThe black drum fish feeds on hard-shelled mollusks, which requires strong, tough, and wear-resistant teeth. This study presents a comprehensive multiscale material and mechanical analysis of the black drum teeth in achieving such remarkable biological function. At microscale, the fluoride- and zinc-doped apatite crystallites in the outer enameloid region are aligned perpendicular to the chewing surface, representing one of the stiffest biomineralized materials found in nature. In the inner enameloid region, the apatite crystals are arranged into intertwisted rods with crystallographic misorientation for increased crack resistance and toughness. At the macroscale, the molariform geometry, the two-layer design based on the outer enameloid and inner dentin, enlarged pulp chamber and the underlying strong bony toothplate work synergistically to contribute to the teeth's crushing resistance.

On the correlation between plastic strain and misorientation in polycrystalline body-centered-cubic microstructures with an emphasis on the grain size, loading history, and crystallographic orientation

The correlation between plastic strain and crystallographic misorientation, grain size, grain orientation, distance from grain boundary, and loading history were investigated experimentally and numerically for body-centered-cubic (BCC) polycrystalline microstructures based on a misorientation deviation (MD) approach. Nine monotonic tensile experiments were performed on two BCC titanium alloys inside a scanning electron microscope (SEM). The influence of reference orientation was explored both at the grain scale and at the mesoscale using electron backscattered diffraction (EBSD). The correlation between global plastic strain and the MD was quantified. The tendency for orientation change was quantified as a function of plastic strain and grain orientation for three crystallographic orientations (i.e., [100], [110], and [111]) with respect to tensile direction. The subpopulation of small grains exhibited a lower level of misorientation dispersion compared with larger grains, and this discrepancy became more pronounced at higher strains. An empirical equation was proposed to estimate the level of misorientation dispersion for individual grains as a function of grain size and global plastic strain level. Two interrupted in-situ SEM experiments were performed, and this resulted in a significantly increased misorientation compared with uninterrupted tests performed to similar plastic strain levels.

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.

Subgrain Boundaries as Sites of Melt Generation and Pathways for Melt Flow: Implications for Rheology From Combined Chemical and Quantitative Orientation Analysis

AbstractWe report a detailed petrographic, compositional, structural, and crystallographic investigation into the partial melting process. Migmatitic samples that record biotite‐dehydration melting in the Wet Mountains of central Colorado preserve textural evidence for partial melting locations and an incipient former melt network. Detailed analysis of partial melting locations was conducted using a combined energy dispersive X‐ray spectroscopy (EDS) and electron backscatter diffraction (EBSD) approach. Cuspate‐shaped films of former melt, now plagioclase, with low apparent dihedral angles and adjacent to rounded and corroded reactant minerals are interpreted as former locations of partial melting. We identified former melt films infiltrating and melting along quartz grains using optical microscopy and EDS and determined crystallographic misorientation across these transects using EBSD. Forty‐two percent of these transects are associated with subgrain boundaries, and the remaining transects are between adjacent quartz grains with various misorientations. Although previous work has emphasized grain boundaries and triple junctions as sites for melting, the presence of over 40% of the former melt films developed along subgrain boundaries suggests that these are favorable and potentially preferred locations for partial melting. Consequently, melting along subgrain boundaries must be integral to the evolution of partial melt networks and will increase melt network interconnectedness and generate a finer grain size, enhancing permeability and leading to focused melt flow. Given that these factors exert a fundamental control on crustal rheology, the role of melting and migration along subgrain boundaries should be investigated within diverse crustal and mantle lithologies and incorporated into models of partial melting.

Space weathering of iron sulfides in the lunar surface environment

Alteration of iron sulfides on the lunar surface by space weathering is poorly understood. We examined space weathering features of iron sulfides in lunar mature soil grains using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM observations reveal that iron sulfides have vesicular textures and iron whiskers on their surfaces. Iron sulfides observed using TEM are troilite and NC-pyrrhotite. The space-weathered rim on the iron sulfides is characterized by crystallographic misorientations and the disappearance of superstructure reflections of troilite in electron diffraction patterns. These crystallographic modifications are probably produced by solar wind irradiation. The rim contains opened vesicles that are aligned along the c-plane of the sulfides, as well as numerous tiny vesicles. The Fe/S ratio at the surface of the rim is higher than in non-altered regions, indicating selective sulfur loss from the surface. Iron whiskers protrude from the space weathered rim and consist of polycrystalline metallic iron. The sulfide rims and the iron whiskers are both coated with vapor-deposited materials rich in O and Si. The combined processes driven by the solar wind irradiation, heating during impact events, solar UV radiation, and the thermal cycling may cause vesicular textures, selective sulfur escape from the iron sulfides, and the formation of the iron whiskers. The rim textures support the notion that the enrichment of heavy sulfur isotopes in mature lunar soils is caused by space weathering of iron sulfides. The space weathered rims on lunar iron sulfides are similar to those observed in regolith samples from asteroid Itokawa. Therefore, alterations of sulfide surface might be common among airless bodies in the solar system.

Impact of grain orientation and phase on Volta potential differences in an additively manufactured titanium alloy.

This work introduces a method for co-localized multi-modal imaging of sub-μm features in an additively manufactured (AM) titanium alloy. Ti-6Al-4V parts manufactured by electron beam melting powder bed fusion were subjected to hot isostatic pressing to seal internal porosity and machined to remove contour–hatch interfaces. Electron microscopy and atomic force microscopy-based techniques (electron backscatter diffraction and scanning Kelvin probe force microscopy) were used to measure and categorize the effects of crystallographic texture, misorientation, and phase content on the relative differences in the Volta potential of α-Ti and β-Ti phases. Given the tunability of additive manufacturing processes, recommendations for texture and phase control are discussed. In particular, our findings indicate that the potential for micro-galvanic corrosion initiation can be regulated in AM Ti-6Al-4V parts by minimizing both the total area of {111} prior-β grains and the number of contact points between {111} β grains and α laths that originate from {001} prior-β grains.

СПЕЦИФИКА ПРИМЕНЕНИЯ РЕНТГЕНОВСКИХ МЕТОДОВ «КАЧАНИЯ» И ЛАУЭ ПРИ ОЦЕНКЕ КАЧЕСТВА СТРУКТУРЫ ОТЛИВОК НИКЕЛЕВЫХ ЖАРОПРОЧНЫХ СПЛАВОВ

Systematically analyzes and justifies the characteristics of equipment operating in monochromatic radiation by the «swing» method and in polychromatic radiation by the Laue method in relation to the specifics of controlled samples in the technology of single-crystal casting from nickel heat-resistant alloys. The main application of the «swing» method is the mass control of seed blanks, seedings, growth cones of samples and blades. The main application of the Laue method is local measurements of block misorientation in the casting of the turbine blade, determination of the crystallographic orientation misorientation in controlled areas on the blade. An optimized configuration is proposed for a compact modification of a diffractometer operating in monochromatic radiation for mass control of the structure in production.