Electron Backscatter Diffraction Study Research Articles

Kyanite-muscovite-dumortierite vein mineralization mechanisms from advanced microstructural analysis using EBSD

Abstract Dumortierite, an aluminous borosilicate mineral, is relatively rare in Earth’s crust, but it is the second most abundant aluminous borosilicate after tourmaline. Boron is an element with many uses in modern societies worldwide, from health products to wind turbine blades for clean energy, but of limited availability and at future risk of supply. Only a limited number of studies have been published on dumortierite mineralization processes and the factors that control its abundance and distribution remain poorly understood. Here we present the first comprehensive electron backscatter diffraction (EBSD) study of dumortierite mineralization mechanisms in kyanite-muscovite-dumortierite veins occurring in the metapelites of the Amgaon Gneiss Supracrustals, in the Girola hill area, Sakoli region, Central India. Advanced microstructural and chemical analyses show that mixed-mode brittle-viscous deformation in kyanite, by fracturing and easy glide on (100) [001] slip system, facilitates fluid-rock interactions with reactive hydrothermal fluids rich in B, F, and K and containing Na, Ti, Mg, Fe and Pt. These interactions cause the dissolution of kyanite along fracture and cleavage surfaces and the precipitation of muscovite (F = 0.32 wt %) and topaz (F = 16.48 wt %). The motion of ripplocation defects in muscovite facilitates fluid migration along cleavage surfaces and crystallisation of dumortierite needles within these surfaces. Fluid flux removes silica in solution from the system, so reactions may continue. The observed mineral assemblage, the microstructural signature of kyanite and muscovite, the moderate fluorine content of topaz, and low fluorine content of muscovite, together suggest that dumortierite mineralization results from hydrothermal activity, possibly in a transitional magmatic-hydrothermal environment, likely at P > 2.5 kbar and 400°<T < 550°, that could be linked with granite intrusions in the area. Using EBSD we demonstrate that dumortierite mineralization is focussed along muscovite basal cleavage surfaces and dumortierite needle elongation is likely controlled by the fluid flux direction. These new results advance our understanding of dumortierite mineralization mechanisms and conditions and have important implications for our understanding of the distribution of this aluminous borosilicate mineral in muscovite-rich rocks.

A quasi-in-situ EBSD study on abnormal grain growth in 2219 aluminum alloy friction stir welded joints during post-weld heat treatment

Abnormal grain growth occurs in the friction stir welds of 2219 aluminum alloy during the solution treatment. To further investigate abnormal grain growth, the quasi-in-situ electron backscatter diffraction (EBSD) experiment, including the EBSD testing and heating by thermal simulation testing machine, was proposed to observe the grain growth process in the weld. The results show that the abnormal grain growth behavior in the stir zone and the thermo-mechanically affected zone is different, and different microstructures at different positions in the weld promote the growth of abnormal grains. In the stir zone, the modified Humphreys’ model is used to analyze the abnormal grain growth behavior. The grains with an advantage size and low strain are more likely to grow abnormally. The non-uniform pinning caused by the dissolution of second-phase particles further promotes abnormal grain growth. In the thermo-mechanically affected zone, the abnormal grains are formed by unstrained equiaxed grains near the stir zone or recrystallized sub-grains. The growth of abnormal grains in the thermo-mechanically affected zone is a strain-induced grain boundary migration process. The research is helpful to understand the abnormal grain growth in friction-stir welds during post-weld heat treatment.

Electron backscatter diffraction study and unified constitutive model of dynamic recrystallization behavior of As-forged ERNiCrMo-3 alloy

The hot deformation behavior of as-forged ERNiCrMo-3 alloy was studied through isothermal compression tests at temperatures ranging from 1000 to 1150℃ and strain rates of 0.01–10 s−1. The microstructure evolution mechanism was analyzed using scanning electron microscopy(SEM) and electron backscatter diffraction(EBSD). Results indicate that with increased strain and temperature, dynamic recrystallization becomes more evident, low-angle grain boundaries transform into high-angle ones, and twins lose their twinning nature. Recrystallization decreases with increasing strain rate from 0.01 to 1 s−1, but at 10 s−1, due to high dislocation density, adiabatic heating, recrystallization is enhanced. The primary DRX mechanism is discontinuous dynamic recrystallization(DDRX) via grain boundary bulging, supplemented by continuous dynamic recrystallization(CDRX) through lattice rotation and strain-induced subgrain boundary transformation. Twin boundaries provide additional nucleation sites and promote recrystallized grain growth. Considering the critical strain for DRX initiation, the nucleation rate of DRX grains, and the size of DRX grains, a unified constitutive model coupling flow behavior and microstructure evolution was developed, which can accurately and reasonably describe the flow behavior and microstructural changes of ERNiCrMo-3 alloy.

In-situ high-temperature EBSD study of austenite reversion from martensite, bainite and pearlite in a high-strength steel

The austenite (γ) reversely transformed from lath martensite (LM), lath bainite (LB), granular bainite (GB) and pearlite+ferrite (P+F) in a high-strength steel was studied at high temperatures using in-situ electron backscatter diffraction (EBSD). The memory effect of initial γ significantly affects the nucleation of the reverted γ in LM and GB structures, while a weak influence on that of LB and P+F structures. This results in a significant difference in γ grain size after complete austenitization, with the first two obtaining larger γ grains while the latter two are relatively small. Crystallographic analysis revealed that the reverted γ with acicular morphology (γA), most of which maintained the same orientation with the prior γ, dominated the reaustenitization behavior of LM and GB structures through preferential nucleation within γ grains and coalesced growth modes. Although globular reverted γ (γG) with random orientation or large deviation from the prior γ can nucleate at the grain boundaries or within the grains, it is difficult for it to grow and play a role in segmenting and refining the prior γ due to the inhibition of γA coalescing. For LB and P+F structures, the nucleation rate of intragranular γG increases with increasing temperature, and always shows a random orientation. These γG grains can coarsen simultaneously with the intergranular γG, ultimately playing a role in jointly dividing and refining the final γ grains. Research also found that the differences in the effects of four different microstructures on reverted γ nucleation are closely related to the variant selection of the matrix structure, as well as the content and size of cementite (θ). High density of block boundaries induced by weakening of variant selection and many fine θ formed in the lath are the key to promoting LB structure to obtain more intragranular γG formation, as well as the important role of the large-sized θ in P+F structure.

Effect of interlayer scan rotation on structure-property relationship of directed energy deposited CoCrNi medium entropy alloy

Laser-based Additive Manufacturing (AM) is sought to be a prevalent technique to synthesize medium to high entropy alloys. However, the anisotropy, temperature distribution, and residual stresses in Laser-based AM are some of the major problems that need to be addressed. The effect of interlayer scan rotation on microstructure, texture evolution, and tensile properties of laser-based directed energy deposited CoCrNi are investigated in this study. The electron backscatter diffraction studies revealed the strong 〈001〉 cubic crystallographic texture along the build direction (YZ-plane) without scan rotation. However, there is no preferred grain orientation observed with interlayer scan rotations. The 〈111〉 fiber texture and 〈111〉〈101〉 fiber texture, respectively, are obtained with 67° and 90° scan rotation strategies. The randomized grain orientation due to fiber texture formation enhanced strength significantly with little improvement in ductility. In addition, the substructure refinement is also observed after incorporating scan rotation. Moreover, the present work suggests that nearly isotropic strength and elongation are obtained with 67° rotations.

Solute segregation, clustering and interphase precipitation in Ti-Mo-Nb microalloyed steel studied by correlated electron backscattering diffraction and atom probe tomography

Site-specific atom probe tomography coupled with electron back scattering diffraction studies were used for the first time to elucidate the multi-element solute segregation and clustering at austenite-ferrite interface during early stages of phase transformation in Fe-Mn-Si-C steel alloyed with Ti, Mo and Nb. The results have shown the existence of negligible partitioning local equilibrium at interfaces with segregation of C, Mn, Ti and Mo to interfaces having the angle deviation in the range from 2.9 to 12° from Kurdjumov-Sacks orientation relationships (K-S ORs), but either irregular incident planes or the ones not following the matching according to K-S ORs. The segregation of Nb was less common, which was linked to the earlier occupancy of interfaces by Ti and Mo. Variation in solute segregation along the same interfaces is highlighted. Presence of clusters within and in close proximity to the interface is detected. The links between interface orientation, solute segregation, clustering and interphase precipitation are discussed.

The effect of annealing on micro-hardness of molybdenum single crystals

Molybdenum (Mo) crystals exhibit excellent mechanical properties such as high yield strength, high elastic modulus, very high melting point, and excellent corrosion resistance, making them a suitable choice for various industrial applications. The mechanical behaviour of these crystals has been investigated through tension, compression, and indentation experiments. The indentation experiments on annealed Mo single-crystal thin film show an increase in hardness with increase in annealing temperature from 400 °C–650 °C. However, it is not clear whether this behaviour is specific to the Mo thin films or these are applicable to the bulk samples of single crystals also. In order to address these issues, the Vickers indentation experiments are performed on as-received and annealed samples of (100) -, (110) -, and (111) -oriented Mo single crystals. The results show that the low-temperature annealing leads to an increase in micro-hardness by 9% for (100) oriented crystals. The x-ray diffraction (XRD), electron backscatter diffraction (EBSD) and energy dispersive x-ray spectroscopy (EDS) studies have shown that there is a drop in the number of dislocation sources or dislocation density ( ρ ) with no high-angle grain boundary formation or any microstructural changes or any oxide formation. This necessitates to enhance the applied stress required for significant yielding (or yield strength) which results in an increase in the hardness. Based on experimental observations, a hardening mechanism governed by dislocation annihilation during annealing has been proposed in the present study.

An electron backscatter diffraction study of monazite: Linking the time-deformation path

Monazite, (Ce,REE)PO4, is a common accessory mineral used to quantify the timing and duration of tectono-metamorphic processes in (poly)metamorphosed orogenic terranes. As monazite frequently yields a spread of dates, there can be ambiguity linking age domains to specific metamorphic reactions and/or deformation events. This study aims to: (1) discern the effect of deformation on the monazite crystal structure; (2) understand how dynamic recrystallisation and dissolution-precipitation mechanisms are recorded by microtexture and/or the distribution and concentration of elements and isotopes within the monazite; and (3) assess the usefulness of microtextural imaging for the interpretation of complex petrochronological datasets.Monazites are analysed from several different geological settings including, the Himalaya (India), Western Gneiss Region (Norway), Snake Range (Nevada, USA), and Madagascar. Here, combined laser-ablation split stream isotopic (U-Th/Pb) and trace element analysis and Electron Backscatter Diffraction (EBSD) are used to investigate links between monazite (re)crystallisation/precipitation mechanisms, microtextures, age and trace-element distribution in individual grains. The studied monazite display a variety of microtexture including (001)[100] and (120)[120] (deformation) twins, micron-scale lattice rotation, and sub-grain boundaries.Observed monazite microtextures are interpreted to have formed during ductile deformation. Microtextures typically coincide with geochemically distinct, younger monazite, suggesting that crystallographic defects focus coupled dissolution-precipitation mechanisms during deformation and metamorphism. Crystallographic defects (including twins and sub-grains) are interpreted to be significant pathways for fluid, enabling coupled dissolution-precipitation of chemically distinct monazite during ductile deformation and metamorphism. This study highlights the power of combining traditional petrochronology approaches with microtextural imaging to better link monazite ages to specific deformation events.

Electron backscatter diffraction (EBSD) study of elongatoolithid eggs from China with microstructural and parataxonomic implications

AbstractElectron backscatter diffraction (EBSD) has been widely used in recent studies of eggshells for its convenience in collecting in situ crystallographic information. China has a wide variety of dinosaur eggshells, although nearly none have been studied with this technique. Elongatoolithid eggs include many oogenera, although the microstructural differences of some were not highly appreciated, leading to several parataxonomic problems. In this paper, we surveyed seven elongatoolithid oogenera in China using EBSD in order to acquire more information about their microstructural variation. It is shown in this paper that in some elongatoolithid eggshells, scaly calcite grains that form the squamatic ultrastructure are not the only form of calcite in the continuous layer. Large columnar grains separated by high-angled grain boundaries and slender subgrains separated by radially arranged low-angled grain boundaries could exist in certain areas of the eggshells such as Macroolithus and Macroelongatoolithus. This paper discusses the criteria for identifying squamatic ultrastructure and proposes type I (rich in rugged high-angled grain boundaries) and type II (rich in both rugged high- and low-angled grain boundaries) squamatic ultrastructures. A pathological layer is found in Undulatoolithus pengi. An external zone is identified in the eggshell of Heishanoolithus changii, which does not support its position within the oofamily Elongatoolithidae. We argue that Paraelongatoolithus no longer belongs to Elongatoolithidae based on a combination of reticulated ornamentation, columnar continuous layer, and acicular mammillae. The high structural variation in elongatoolithid eggshells also implies that it may be inappropriate to relate all previous elongatoolithid eggshells to oviraptorosaurs and assume they are non-monophyletic.

Role of residual stress in the failure of HF-ERW welded tubes

High-frequency electric resistance welding is used for manufacturing hydro formable tubes. Tube forming and welding results in the formation of residual stress. The hole drilling technique was used to evaluate the residual stress of the welded tube. Tensile residual stress of varying magnitude was observed at different locations on the tube. The weld, heat affected zone was observed to have the highest residual stress as a result of phase transformation, forming and gradually reduced towards the parent material. The generated tensile residual stress led to failure of the tube during mechanical evaluation. Additionally, electron backscattered diffraction studies (EBSD) of the fusion line and the thermo-mechanically heat-affected zone were found to have goss and cube texture. These detrimental textures can lead to easy crack propagation in the presence of defects along the fusion line. A post-weld heat treatment (PWHT) was carried out to alleviate the tensile residual stress and alter the weld microstructure. PWHT helped transform the bainite in the weld to ferrite and pearlite. The inter-critical annealing significantly reduced the tensile residual stress along the circumferential direction resulting in improved formability.

Unraveling the effects of nano-grained microstructure on mechanical behavior, corrosion, and in vitro biocompatibility of 316L austenitic stainless steel

Nanograins are often beneficial in achieving better cytocompatibility for metallic implants. In this work, we have achieved grains from the micro to nano range in 316L austenitic stainless steel by a combination of cryo-rolling (50%, 70%, and 90% thickness reduction) followed by annealing (750–1000 °C for 2–20 min). The combined effect of grain refinement along with texture on its mechanical, corrosion, and in vitro cellular behavior was thoroughly investigated. Microstructural observations revealed nanograins formation (grain size = 144 nm) only for the 90CRA sample, whereas grain refinement in the micron range was observed for 0-70CRA samples. Electron backscatter diffraction (EBSD) studies showed fully austenitic structures for all the annealed samples while low Kernel Average Misorientation (KAM) values indicated strain-free microstructures. Orientation distribution function (ODF) maps showed the presence of strong γ-fiber (<111>||ND) and weak α-fiber (<110>||ND) in the 90CRA sample. The grain refinement led to an increase in the yield strength and ultimate tensile strength from 470.6 ± 16.21 MPa and 858.35 ± 31.82 MPa (0CRA) to 1662.06 ± 58.44 MPa and 2112.3 ± 51.62 MPa (90CRA), respectively. The potentiodynamic polarization study revealed that the corrosion rate of the 90CRA sample was about eight times less than that of the 0CRA sample. This was further corroborated by Mott-Schottky analysis, which showed a lowering of both acceptor and donor densities with the reduction in grain size. The evolution of a strong <111> texture during cryo-rolling contributed towards enhanced corrosion resistance of nano-grained 316L. Furthermore, grain refinement improved wettability, which in turn led to better cell proliferation and differentiation. At all culture days, MC3T3-E1 cell proliferation and differentiation were considerably higher for nano-grained 316L micron-sized counterparts. Thus, grain refinement to the nano range is an effective technique for the property enhancement of biomedical implants.

A combined EBSD and machine learning study of predicting deformation twinning in BCC Fe81Ga19 alloy

Compared to face-centered cubic (FCC) metals, body-centered cubic (BCC) metals demonstrate more intricate deformation behavior and microstructural characteristics because of the influence of intrinsic unstable stacking faults and defect structure. To investigate the unique phenomenon of deformation twinning in Fe81Ga19 alloy with BCC structure at moderate temperature and low strain rate, four twin nucleation models were constructed using a combination of electron backscatter diffraction (EBSD) technique and machine learning. These models are aimed to predict twin nucleation of grains and explore the relationship between twin nucleation and microstructural attributes. The study revealed that amongst the 235 grains analyzed during in-situ compressive deformation, 32 grains experienced twinning. Nine attributes influencing twin nucleation were selected and ranked according to their importance. Grain area, average image quality, neighboring grain count, and the Schmid factor of twinning systems exhibited significant influence on twin nucleation. Decision tree and tree ensemble (XGBoost) achieved 94% and 96% accuracy, respectively, on the test set, showcasing robust generalization capability. Due to the optimization of hyperparameters, support vector machine (SVM) and artificial neural network (ANN) exhibited outstanding performance. The ANN model achieved an accuracy of 97% and an F1 score of 0.91 on the test set, while the SVM model achieved an accuracy of 98% and an F1 score of 0.94, indicating superior performance. Furthermore, the study revealed that the twinning stress in Fe81Ga19 alloy exhibited weak responsiveness to temperature during deformation, and the intrinsic factors of grains were identified as crucial factors influencing twin nucleation.

In-situ observation of deformation-induced grain reorientation in 718 Ni alloy microlattices

Microlattices pose ample opportunity for constructing light weight structures for the automotive and aerospace industries. Laser powder bed fusion is an appealing technique to fabricate these structures because of its capabilities to process high-resolution complex architectured structures. In this work we explore the use of a 718 oxide dispersion strengthened alloy to create three microlattice structures designed in nTop, a straight bar, honeycomb and body-centered cubic (BCC) microlattice and investigate the effects of architectures on tensile behavior of the microlattices in a scanning electron microscope. The straight bar configurations deliver high strength but low ductility. The BCC lattices are highly deformable but soft. The honeycomb has an attractive combination of high strength and pronounced work hardening. Furthermore, electron backscattered diffraction studies revealed substantial crystallographic reorientation and grain refinement in the honeycomb lattice during deformation, in contrast to little crystal orientation change in the straight bar specimens. This study suggests that architectures play a significant role in the tensile behavior and deformation mechanisms in metallic materials.

Effects of carbon content on precipitate evolution and crack susceptibility in additively manufactured IN738LC

Hot cracking is a major bottleneck preventing the additive manufacturing community from adopting precipitation-strengthened nickel-base superalloys, such as the IN738LC. Prior literature demonstrates the beneficial outcome of increasing the carbon content within IN738LC to alleviate its hot cracking problem. However, the effect of carbon content on the gamma prime precipitation and grain recrystallization was not fully addressed. Here, we fabricated five sample sets of IN738LC with different carbon contents and subjected these samples to two separate heat treatment processes. The precipitate and grain evolution were monitored under the backscattered electron imaging and electron backscattered diffraction studies. While the carbon addition could assist in addressing the hot cracking problem, horizontal delamination cracks were detected during the fabrication of large samples when the overall carbon content was above 0.4 wt.%, highlighting the need for care when introducing carbon for the purpose of resolving hot cracking.

In-Situ EBSD Study of Phase Transformation in Additively Manufactured Titanium Alloy

The phase transition and grain refinement features of a Ti-6Al-4V alloy are investigated in this study using in-situ high- temperature Electron Backscatter Diffraction (EBSD). The objective of the experiment was to detect the phase transition from Body-Centered Cubic (BCC) to Face-Centered Cubic (FCC) systems at temperatures ranging from 770 to 900 degrees Celsius. Grain refinement techniques such as recrystallization twin generation, Kernel Average Misorientation (KAM), and low-angle grain boundary creation were the focus of this study. According to our research, phase transformation maps taken at 770°C, 810°C, 840°C, and 900°C reveal that a discontinuous recrystallization process was responsible for the transformation and recrystallization. The results of this investigation provide support to the theory that high-temperature treatments may enhance the microstructure of additively made Ti-6Al-4V alloys. At temperatures of 900 °C, the grain structure was evenly polished, and an almost complete phase shift to a face-centered cubic (FCC) shape was observed.

EBSD study of variant reorientation, texture, and twin formation in a martensitic NiTi alloy deformed in compression

Martensitic crystallography plays a vital role in the texture evolution and mechanical properties in Nickel-Titanium (NiTi) shape memory alloys when subjected to deformation. However, their microstructural changes during deformation are not well known and understood. In this study, we systematically investigate the stress-induced change of the microstructure of NiTi shape memory alloy under compression using the electron backscattered diffraction (EBSD) technique, and more specifically the variant reorientation, the evolution of textures, and the formation of twins. The EBSD maps reveal that upon strain the martensite morphologies shift from needle to block and their orientations are strongly reinforced along the loading axis. To quantify these microstructural changes, we used the Interaction Work (IW) associated with the lattice distortion of single variant, which provides a good fit with the experimental observation. A strong dependence of reorientation on the pre-textures of the parent B2 grains was also put in evidence. Other plasticity sources were confirmed such as dislocations and deformation twins. The calculations indicate that, for some specific orientations of parent grains, the active deformation twins could be easier for {011}M twin than that of (201¯)M deformation twin, whereas other orientations only favor the (201¯)M deformation twin.

Determining the habit plane for radial δ-hydrides in a textured zirconium-alloy tube under hoop tensile stress: A theory-experiment approach

The orientation of hydrides with respect to externally applied stress affects the susceptibility of Zirconium (Zr) alloy fuel cladding tubes to through-wall failure. Previous studies have mainly focused on the situation in the absence of external stress, with little attention paid to the situation under applied stress. Hoop tensile stress can cause the reorientation of hydride platelets from the circumferential to the radial direction in the radial textured Zr fuel clad tubes, substantially degrading its hoop ductility. In this study, we used a theory-experiment approach to investigate the radial hydride-matrix orientation relationship. A microstructure criterion was proposed to determine the habit plane of the radial δ-hydrides. Our results demonstrate that radial δ-hydrides predominantly form on the pyramidal 101¯1α plane of α-Zr with 101¯1α−Zr//111δ−hydride. The electron backscatter diffraction study of hydrided Zircaloy-4 tube provides experimental evidence supporting theoretical prediction. The underlying mechanism for this phenomenon is attributed to a competition between tensile stress-assisted hydride nucleation and strain-induced resistance to nucleation.

Lattice preferred orientation of quartz in granitic gneisses from Tso Morari Crystalline Complex, Eastern Ladakh, trans-Himalaya: evaluating effect of Dauphiné twin in dynamic recrystallization during exhumation

Abstract The Tso Morari Crystalline complex (TMCC) of eastern Ladakh, India, is part of the north Indian continental margin and is characterized by eclogitic enclaves embedded within ortho- and paragneisses known as the Puga Gneiss. Two fault zones bound the TMCC: the Karzok fault to the southwest and the Zildat fault to the northeast. In the present study, we carried out Electron Backscatter Diffraction study of quartz of 10 samples collected from the Puga Gneiss. The relict and recrystallized quartz grains were treated separately to understand the deformation conditions of the Puga Gneiss during early and late deformation stages related to UHP metamorphism and final stage of exhumation during retrogression, respectively. Microstructural observations suggest dynamic recrystallization in quartz and plagioclase at different temperature ranges. Misorientation analysis of both relict and recrystallized quartz grains reveals presence of Dauphiné Twins. Lattice preferred Orientation (LPO) of &lt;c&gt; axis of relict quartz grains generally shows more than one point maxima indicating that the relict grains preserve LPO developed during different stages of metamorphism/deformation. On the other hand, LPO of &lt;c&gt; axis of recrystallized grains from Karzok and Zildat fault zones shows asymmetric single girdle either normal or at an angle to the foliation plane, which suggests simple shear. We conclude that grain size reduction and recrystallization of the Puga Gneiss was greatly influenced by Dauphiné Twin and the final exhumation of the TMCC took place in a simple shear environment aided by activity along its two binding fault zones.

Griffinite, Al2TiO5: A New Oxide Mineral from Inclusions in Corundum Xenocrysts from the Mount Carmel Area, Israel

Griffinite (IMA 2021-110), ideally Al2TiO5, is a new mineral from inclusions in corundum xenocrysts from the Mount Carmel area, Israel. It occurs as subhedral crystals, ~1–4 μm in size, together with Zr-rich rutile within a corundum grain. In this study, a mean of eight electron probe microanalyses gave TiO2 44.41 (24), Al2O3 55.13 (18), FeO 0.47 (5), and MgO 0.37 (2), totaling 100.38 wt%, which corresponded, on the basis of a total of five oxygen atoms, to (Al1.97Mg0.02Fe0.01)Ti1.01O5. Electron back-scatter diffraction studies revealed that griffinite is orthorhombic and in the space group Cmcm, with a = 3.58 (2) Å, b = 9.44 (1) Å, c = 9.65 (1) Å, and V = 326 (2) Å3 with Z = 4. The six strongest calculated powder diffraction lines [d in Å (I/I0) (hkl)] are 3.347 (100) (110); 2.658 (90) (023); 4.720 (77) (020); 1.903 (57) (043); 1.790 (55) (200); and 1.688 (44) (134). In the crystal structure, Al3+ and Ti4+ are disordered into two distinct distorted octahedra, which form edge-sharing double chains. Griffinite is a high-temperature oxide mineral, formed in melt pockets in corundum-aggregate xenoliths derived from the upper mantle beneath Mount Carmel, Israel. The new mineral is named after William L. Griffin, a geologist at Macquarie University, Australia.

Effect of He Plasma Exposure on Recrystallization Behaviour and Mechanical Properties of Exposed W Surfaces—An EBSD and Nanoindentation Study

Fusion reactors are designed to operate at extremely high temperatures, which causes the plasma-facing materials to be heated to 500 °C to 1000 °C. Tungsten is one of the target design materials for the plasma-facing diverter components in Tokamak designs, such as ITER, because of its excellent high-temperature strength and creep properties. However, recrystallization due to high temperatures may be detrimental to these superior mechanical properties, while exposure to He plasma has been reported to influence the recrystallization behaviour. This influence is most likely due to the Zener effect caused by He bubbles formed near the surface, which retard the migration of grain boundaries, while at the same time modifying the surface microstructure. This paper reports a study of the effect of plasma exposure at different sample temperatures on the recrystallization behaviour of W at different annealing temperatures. The characterization after plasma exposure and annealing is pursued through a series of post-exposure annealing, followed by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) characterization and nanoindentation to determine the mechanical properties. Here, it is shown that the hardness is closely related to the recrystallization fraction, and that the plasma exposure at a sample temperature of 300 °C slows down the recrystallization more than at higher sample temperatures of 500 °C and 800 °C. Atomic force microscopy (AFM) was subsequently used to determine any changes in pile-up height around the nanoindents, to probe any indication of changes in hardenability. However, these measurements failed to provide any clear evidence regarding this aspect of mechanical behaviour.