Crystallographic Orientation Analysis Research Articles

The effect of hydrous mineral content on competitive strain localization mechanisms in felsic granulites

This study investigates the grain-scale mechanisms that facilitated strain localization in the lower crust within the East Athabasca Mylonite Triangle of northern Saskatchewan, Canada. There, two distinct lithotectonic units, the Upper Deck and Northwestern Domain, are juxtaposed across a km-scale shear zone that has been previously interpreted to record thrust and/or normal-sense displacement. Our study reports new quartz c-axis opening angle, Ti-in-biotite and Ti-in-quartz geothermometry and amphibole-plagioclase geothermobarometry within syn-kinematic phases indicating that both units were deformed and metamorphosed at upper amphibolite to granulite facies (~725 °C and ~0.8 GPa). While sharing similar conditions, the dominant mechanisms of deformation across the two units are strongly linked to modal proportion of syn-kinematic hydrated mineral phases. Detailed microstructural and crystallographic preferred orientation (CPO) analyses reveals that specimens poor in hydrated minerals (<10%) deformed mainly by dislocation creep and dynamic recrystallization allowing it to develop a strong quartz CPO, while in specimens rich in hydrated minerals (>10%) pressure solution and (re)precipitation processes enhanced phase mixing and promoted grain boundary sliding resulting in weakly developed or absent quartz CPO. These results indicate a strong mineralogical and fluid control on deformation and, therefore, which strain softening process (es) may dominate in lower crustal shear zones.

Non-destructive three-dimensional crystallographic orientation analysis of olivine using laboratory diffraction contrast tomography

AbstractX-ray laboratory diffraction contrast tomography (LabDCT) produces three-dimensional (3D) maps of crystallographic orientation. The non-destructive nature of the technique affords the key benefit of full 3D context of these, and other, in situ measurements. This study is the first to apply the technique to any material other than a metal or silicon. We report the first 3D measurements of the crystallographic orientation of olivine, which also makes this study the first to apply LabDCT to (1) a non-metallic, non-cubic system and (2) geological material. First, we scanned fragments of olivine set in resin alongside glass microbeads using LabDCT and absorption contrast tomography (ACT). Then we reconstructed these data assuming an orthorhombic crystal system. We show that: (1) the regions within the sample that index well according to the orthorhombic system correspond to olivine fragments in the ACT image; (2) crystalline regions not corresponding to olivine are not indexed assuming the same lattice parameters; and (3) the diffraction data discriminates crystalline from non-crystalline materials as expected. Finally, we demonstrate that the method resolves sub-degree orientation differences between distinct regions within individual olivine fragments. We conclude that DCT can be applied to the study of rocks and other crystalline materials, and offers advantages over conventional techniques. We also note that LabDCT may offer a solution to the crystallographic measurement of substances that would otherwise be difficult to measure due to challenges in obtaining a perfect sample polish. Future developments to accommodate larger experimental volumes and additional crystallographic systems within a sample promises to expand the applicability and impact of DCT.

Architecture of Anoteropora latirostris (Bryozoa, Cheilostomata) and implications for their biomineralization

Cheilostome Bryozoa Anoteropora latirostris, a colonial marine invertebrate, constructs its skeleton from calcite and aragonite. This study presents firstly correlated multi-scale electron microscopy, micro-computed tomography, electron backscatter diffraction and NanoSIMS mapping. We show that all primary, coarse-grained platy calcitic lateral walls are covered by fine-grained fibrous aragonite. Vertical lateral walls separating autozooid chambers have aragonite only on their distal side. This type of asymmetric mineralization of lateral walls results from the vertical arrangement of the zooids at the growth margins of the colony and represents a type of biomineralization previously unknown in cheilostome bryozoans. NanoSIMS mapping across the aragonite-calcite interface indicates an organic layer between both mineral phases, likely representing an organic template for biomineralization of aragonite on the calcite layer. Analysis of crystallographic orientations show a moderately strong crystallographic preferred orientation (CPO) for calcite (7.4 times random orientation) and an overall weaker CPO for aragonite (2.4 times random orientation) with a high degree of twinning (45%) of the aragonite grains. The calculated Young’s modulus for the CPO map shows a weak mechanical direction perpendicular to the colony’s upper surface facilitating this organism’s strategy of clonal reproduction by fragmentation along the vertical zooid walls.

Deformation conditions during syn-convergent extension along the Cordillera Blanca shear zone, Peru

AbstractStrain localization across the brittle-ductile transition is a fundamental process in accommodating tectonic movement in the mid-crust. The tectonically active Cordillera Blanca shear zone (CBSZ), a ∼200-km-long normal-sense shear zone situated within the footwall of a discrete syn-convergent extensional fault in the Peruvian Andes, is an excellent field laboratory to explore this transition. Field and microscopic observations indicate consistent top-down-to-the-southwest sense of shear and a sequence of tectonites ranging from undeformed granodiorite through mylonite and ultimately fault breccia along the detachment.Using microstructural analysis, two-feldspar and Ti-in-quartz (TitaniQ) thermometry, recrystallized quartz paleopiezometry, and analysis of quartz crystallographic preferred orientations, we evaluate the deformation conditions and mechanisms in quartz and feldspar across the CBSZ. Deformation temperatures derived from asymmetric strain-induced myrmekite in a subset of tectonite samples are 410 ± 30 to 470 ± 36 °C, consistent with TitaniQ temperatures of 450 ± 60 to 490 ± 33 °C and temperatures &gt;400 °C estimated from microstructural criteria. Brittle fabrics overprint ductile fabrics within ∼150 m of the detachment that indicate that deformation continued to lower-temperature (∼280–400 °C) and/or higher-strain-rate conditions prior to the onset of pervasive brittle deformation. Initial deformation occurred via high-temperature fracturing and dissolution-precipitation in feldspar. Continued subsolidus deformation resulted in either layering of mylonites into monophase quartz and fine-grained polyphase domains oriented subparallel to macroscopic foliation or the interconnection of recrystallized quartz networks oriented obliquely to macroscopic foliation. The transition to quartz-controlled rheology occurred at temperatures near ∼500 °C and at a differential stress of ∼16.5 MPa. Deformation within the CBSZ occurred predominantly above ∼400 °C and at stresses up to ∼71.4 MPa prior to the onset of brittle deformation.

Microstructural and crystallographic study of hydrogen-assisted cracking in high strength PSB1080 steel

The microstructural and crystallographic study of hydrogen-assisted cracking in high strength PSB1080 steel was conducted. The results indicate that the mechanical properties of PSB1080 steel are seriously deteriorated in the presence of hydrogen, which is ascribed to the coupling effect of hydrogen-assisted cracking from the O–Al–Si–Ca inclusion and accelerated phase transformation from the austenite to the martensite due to hydrogen. The hydrogen uncharged sample exhibits dimple fracture pattern, whereas the fracture surface of hydrogen charged sample consists of three zones, i.e., quasi-cleavage zone, a mixed zone of quasi-cleavage and dimple as well as dimple zone. Crystallographic orientation analysis beneath the three zones demonstrates that the proportion of low angle grain boundary is the highest, followed by high angle grain boundary and then medium angle grain boundary, and the high Kernel Average Misorientation region facilitates hydrogen-assisted crack propagation. Additionally, the grains oriented with {001}//ND, {110}//ND, {123}//ND exhibit the high possibility of hydrogen-assisted cracking. This suggests that these oriented grain textures should be reduced to design the resistance-hydrogen embrittlement alloys.

Correlation between crystallographic and microstructural features and low hysteresis behavior in Ni50.0Mn35.25In14.75 melt-spun ribbons

In this work, crystallographic, microstructural and magnetocaloric investigations were performed on textured Ni50Mn35.25In14.75 melt-spun ribbons with low thermal (6 K) and magnetic-field induced hysteresis (−0.73 J kg−1 at 2 T) and moderate maximum magnetic entropy change ΔSMmax (11 J kg−1 K−1 at 5 T) at room temperature (302 K). The austenite in the ribbons crystallizes into a L21 structure, whereas martensite has a monoclinic incommensurate 6 M modulated structure as determined with the superspace theory. By means of electron backscatter diffraction technique, the morphological and crystallographic features of microstructure were systematically characterized. Ribbons possess a fine microstructure with an average grain size (initial austenite phase) of around 10 μm, whereas the 6 M martensite has a self-accommodated microstructure with 4 kinds of twin-related martensite variants. During inverse martensitic transformation, the austenite prefers to nucleate at the grain boundaries of initial austenite. By means of cofactor conditions and crystallographic orientation analyses, the good geometrical compatibility between austenite and martensite was confirmed. Based on the crystal structure and microstructure information obtained, the reason of the low thermal hysteresis was discussed.

Crystallographic feature of hydrogen-related fracture in 2Mn-0.1C ferritic steel

The present paper investigated crystallographic feature of hydrogen-related fracture in a 2Mn-0.1C steel having a simple ferritic microstructure. We found that the mechanical properties (in particular post-uniform elongation) were degraded by concurrent hydrogen-charging. Most of the fracture surfaces (over 90%) of the concurrently hydrogen-charged specimens showed quasi-cleavage morphologies with serrated markings, but no intergranular fracture surface was observed. Through a detailed crystallographic orientation analysis using EBSD, we have clarified that micro-cracks formed at ferrite grain boundaries and the micro-cracks propagated inside grains along crystallographic {011} planes of ferrite, leading to the quasi-cleavage fracture. Hydrogen micro-print technique revealed that hydrogen accumulated along ferrite grain boundaries under tensile-loading. On the basis of the obtained results, we propose that the fracture on {011} planes is an intrinsic characteristic of hydrogen-related quasi-cleavage fracture in steels having BCC phases.

Grain boundary precipitation behavior of δ-Ni3Nb (D0a) phase in a Ni-Nb-Fe ternary model alloy

Aiming at covering grain boundary (GB) with a geometrically close-packed (GCP) type intermetallic phase in Ni-based superalloys, GB precipitation behavior of the δ-Ni3Nb phase with the D0a structure in the A1 matrix is investigated using a model alloy Ni-12Nb-3Fe. The D0a phase precipitates on GB prior to grain interior (GI). The precipitation of D0a phase tends to take place in a continuous manner above its nose temperature (1373 K) and in a discontinuous manner below the temperature. The area fraction of a GB covered by the precipitate (ρ) significantly differs by GB in aging at 1423 K, i.e. between 0 and 80% in short time aging and between 30 and 100% in long time aging, while their average area fraction (ρ¯) increases up to about 75% after long time aging. The observed large difference in ρ is found to be enhanced in the growth stage of the precipitation. A crystallographic orientation analysis indicates that the difference may be caused by the geometry of the habit planes, {111} in the matrix phase, with respect to the GB plane; that is, in the case that one of the habit planes is nearly parallel to the GB plane, the D0a phase grows along the GB, resulting in high ρ, while the phase grows towards GI when any habit planes are inclined to the GB plane, resulting in low ρ. A multi-step heat treatment is proposed to suppress the growth of the precipitates towards GI.

Analysis of crystallographic preferred orientations of experimentally deformed Black Hills Quartzite

Abstract. The crystallographic preferred orientations (textures) of three samples of Black Hills Quartzite (BHQ) deformed experimentally in the dislocation creep regimes 1, 2 and 3 (according to Hirth and Tullis, 1992) have been analyzed using electron backscatter diffraction (EBSD). All samples were deformed to relatively high strain at temperatures of 850 to 915 °C and are almost completely dynamically recrystallized. A texture transition from peripheral [c] axes in regime 1 to a central [c] maximum in regime 3 is observed. Separate pole figures are calculated for different grain sizes, aspect ratios and long-axis trends of grains, and high and low levels of intragranular deformation intensity as measured by the mean grain kernel average misorientation (gKAM). Misorientation relations are analyzed for grains of different texture components (named Y, B, R and σ grains, with reference to previously published prism, basal, rhomb and σ1 grains). Results show that regimes 1 and 3 correspond to clear end-member textures, with regime 2 being transitional. Texture strength and the development of a central [c]-axis maximum from a girdle distribution depend on deformation intensity at the grain scale and on the contribution of dislocation creep, which increases towards regime 3. Adding to this calculations of resolved shear stresses and misorientation analysis, it becomes clear that the peripheral [c]-axis maximum in regime 1 is not due to deformation by basal 〈a〉 slip. Instead, we interpret the texture transition as a result of different texture forming processes, one being more efficient at high stresses (nucleation or growth of grains with peripheral [c] axes), the other depending on strain (dislocation glide involving prism and rhomb 〈a〉 slip systems), and not as a result of temperature-dependent activity of different slip systems.

Microstructural and crystallographic features of hydrogen-related fracture in lath martensitic steels

ABSTRACTThis paper summarised the microstructural and crystallographic features of hydrogen-related fracture under tensile deformation in martensitic steels. The specimens with relatively low strength exhibited quasi-cleavage fracture. Crystallographic orientation analysis demonstrated that the quasi-cleavage fracture occurred on {011} planes. On the other hand, the macroscopic fracture surface morphologies of the specimens with relatively high strength appeared to be intergranular-like. However, nature of the fracture was somewhat different from a typical intergranular fracture, and the fracture surfaces consisted of facets parallel to {011} planes on a microscopic level. Based on the experimental results, we concluded that the crystallographic feature of {011} plane itself had an important role on the hydrogen-related fracture.This paper is part of a thematic issue on Hydrogen in Metallic Alloys

Microstructural and Crystallographic Insights in a Martensite/Austenite Dual Phase Ni–Mn–Sb Alloy

For Ni–Mn–Sb multifunctional alloy, its microstructure and crystallographic information are decisive factors for its multiple magnetic field induced properties, such as magnetic field induced shape memory effect, magneto‐caloric effect, exchange bias effect, and so on. While, studies on such field are rarely conducted. In the present work, a thorough study on microstructural features and crystallographic characteristics has been conducted in a martensite/austenite dual phase coexisting polycrystalline Ni50Mn37Sb13 alloy. Results show that the martensite is self‐organized in plates in the original austenite. The intra‐plate martensite presents a fine lamellar microstructure and each fine lamella corresponds to one martensite variant. Crystallographic orientation analysis indicates that each martensite plate exists four differently oriented martensite variants and they can form three types of twins, type I, type II, and compound twin. Trace analysis results show that the interface between adjacent variants are their twinning plane K1. Further investigation on martensitic transformation orientation relationship reveals that the Pitsch orientation relationship, specified as //and //, is the effective one from austenite to martensite. All the above results offer basic microstructural and crystallographic information on Ni–Mn–Sb alloys and can be useful for further investigation on property optimization of these alloys.

Role of Different Kinds of Boundaries Against Cleavage Crack Propagation in Low-Temperature Embrittlement of Low-Carbon Martensitic Steel

The present paper investigated the relationship between low-temperature embrittlement and microstructure of lath martensite in a low-carbon steel from both microstructural and crystallographic points of view. The fracture surface of the specimen after the miniaturized Charpy impact test at 98 K (−175 °C) mainly consisted of cleavage fracture facets parallel to crystallographic {001} planes of martensite. Through the crystallographic orientation analysis of micro-crack propagation, we found that the boundaries which separated different martensite variants having large misorientation angles of {001} cleavage planes could inhibit crack propagation. It was then concluded that the size of the aggregations of martensite variants belonging to the same Bain deformation group could control the low-temperature embrittlement of martensitic steels.

Precipitation of secondary alpha in competition with epitaxial growth of primary alpha in two-phase titanium alloys

The significant variation of microstructure features, i.e. volume fraction, size of secondary α phase, due to β→α phase transformation in heat treatment of two-phase titanium alloys can directly affect the mechanical properties. Understanding the nucleation mechanism and modeling the precipitating of secondary alpha phase with existed primary equixed-alpha phase are critical to precisely control the microstructure. In the present work, sympathetic nucleation mode is proposed by crystallographic orientation analysis and validated by calculating the nucleation energy barrier. Then, it is found that the growth of primary α phase competes with precipitation of secondary α phase by consuming the matrix supersaturation related to the driven force for precipitating. By considering the effects of the growth of primary α phase and thermal history on diffusion field around secondary α phase, and introducing a ledge growth mechanism-related factor, a physically founded fast-acting model is developed to predict the precipitation process during cooling. Good agreements between the experimental and computed results are obtained when applied to TA15 alloy with different original microstructures.

Defining shear zone boundaries using fabric intensity gradients: An example from the east-central Nepal Himalaya

Uranium-lead (U-Pb) zircon geochronology, whole-rock geochemistry, and petrographic observations indicate that specimens from a suite of variably deformed granite and orthogneiss from the Okhaldungha region of east-central Nepal share a common origin. Microtextural characterization and quartz crystallographic fabric preferred orientation analyses of these same specimens outline a strain gradient that marks the location of a shear zone boundary. The location of this boundary, at the base of the orthogneiss, coincides with one of the interpreted locations of the Main Central thrust, though it cannot be uniquely identified as such. This study provides the first steps toward empirical constraints on the location and geometry of thrust structures in the region, helping to clarify the complex local kinematic framework. These methods not only help in assessing orogenic models of the Himalaya, but may also be applied to investigating other orogenic systems where the potential location of shear structures is contested.

Cooperative strain accommodation over grains in martensitic transformation from Fe-Ni nanocrystalline austenite

This paper reports an investigation of martensitic transformation behaviour from austenite with various grain sizes ranging from 290 nm to 34 μm in an Fe–Ni alloy fabricated by electrodeposition and subsequent heat treatment. We confirmed that martensite morphology changed from lath to thin plate with decreasing the austenite grain size. Crystallographic orientation analysis revealed that the variants of thin plate martensite formed in the austenite with relatively coarse grains achieved self-accommodation of the transformation strain inside one austenite grain. In contrast, the transformation strain accompanying martensitic transformation from the ultrafine-grained or nanocrystalline austenite was not accommodated by the martensite variants formed in one austenite grain but accommodated cooperatively by those formed in the several adjacent austenite grains.

Crystallographic orientation analysis in HDDR process of anisotropic Nd-Fe-B magnet powders

Microstructural changes and crystallographic orientation information in the hydrogenation-decomposition-desorption-recombination (HDDR) process of Nd-Fe-B alloy were investigated using electron backscatter diffraction (EBSD) and precession electron diffraction (PED) in order to understand the mechanism of anisotropy inducement in the HDDR process. Recombined Nd2Fe14B grains were found to nucleate at the interfaces between NdH2 and α-Fe grains and to have a [001]-oriented texture from the beginning of the recombination reaction. The Fe grains form with alignment of one of the 〈113〉 directions at decomposed stage. This suggests that α-Fe most likely induces texture development of recombined Nd2Fe14B.

Trace element homogeneity from micron- to atomic scale: Implication for the suitability of the zircon GJ-1 as a trace element reference material

The quality of a chemical reference material relies on the fact that the composition of the material is homogeneous across all scales. A series of different techniques have been used to evaluate the trace element homogeneity of the GJ-1 reference zircon from the micron- to atomic scale. Cathodoluminescence imaging was conducted along with quantitative crystallographic orientation analysis and trace element analysis using laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). The nanometre-scale homogeneity was evaluated by analysing five mineral tips using atom probe tomography, which provides atomic scale three dimensional chemical reconstructions with unprecedented spatial resolution. Results show that the GJ-1 reference zircon is homogeneous at all scales, both structurally and chemically. Crystallographic orientation data confirms that this gem quality zircon has no detectable internal crystallographic orientation changes such as crystal-plastic deformation features or cracks. No mineral inclusions were found. Atom probe tomography shows that there is a lack of any chemical clustering or other modes of spatially defined elemental accumulation or depletion for the most abundant trace elements such as Y, Yb and Hf. This finding is supported by LA-ICPMS data revealing homogeneity within the analytical precision. Trace elements of significant abundance include P, Yb, Y, U and Hf, with contents of 30±6, 65±2, 238±5, 284±14 and 6681±57ppm, respectively. Hence, the GJ-1 zircon used as a reference zircon for UPb and Hf-isotopic studies is also a suitable zircon reference material for trace element analyses.

Effects of a high magnetic field on the primary zinc-rich crystals in hypoeutectic Zn-Sn alloy

The effects of a high magnetic field on the primary zinc-rich crystals during the solidification process of hypoeutectic Zn-Sn were investigated, along with the analysis of crystallographic orientations of them. The results show that the primary zinc-rich crystals in two dimensions show column-like or dendritic forms whether without and with the HMF. However, they are highly aligned and textured by the application of a high magnetic field: with the longer axis parallel to but the crystallographic c axis perpendicular to the magnetic field. The two-dimensional forms of the primary zinc-rich crystals are related to their orientations relative to the observation planes. The orientation and alignment modification by the magnetic field arises from the induced magnetic torques due to the magnetocrystalline anisotropy of the zinc-rich crystals, which makes them in energetically optimal orientations.

Fracture surface topography analysis of the hydrogen-related fracture propagation process in martensitic steel

The hydrogen-related fracture propagation process in martensitic steel was investigated through crystallographic orientation and fracture surface topography analyses. The hydrogen-related fracture surface consisted of three typical surfaces, namely smooth surfaces, surfaces with serrated markings, and surfaces with dimples. Crystallographic orientation analysis suggested that the smooth surface was generated by intergranular fracture at prior austenite grain boundaries, and the surface with serrated markings originated from quasi-cleavage fracture propagated along \(\{011\}\) planes. According to the reconstructed fracture propagation process by fracture surface topography analysis, the intergranular fracture at prior austenite grain boundaries initiated and propagated suddenly at the early stages of fracture. The quasi-cleavage fracture along \(\{011\}\) planes then gradually propagated within the prior austenite grains. At the final stages of fracture, ductile fracture accompanied by dimples occurred around the edge of the specimen. The results clearly indicated that the fracture propagation path changed with the proceeding fracture from the prior austenite grain boundaries to along \(\{011\}\) planes within the prior austenite grains.

Carbonado revisited: Insights from neutron diffraction, high resolution orientation mapping and numerical simulations

One of the most controversial diamond types is carbonado, as its origin and geological history are still under debate. Here, we investigate selected carbonado samples using neutron diffraction and high resolution orientation mapping in combination with numerical simulations. Neutron diffraction analyses show that fine grained carbonado samples exhibit a distinct lack of crystallographic preferred orientation. Quantitative crystallographic orientation analyses performed on transmission electron microscope (TEM) sections reveal that the 2–10μm grains exhibit locally significant internal deformation. Such features are consistent with crystal plastic deformation of a grain aggregate that initially formed by rapid nucleation, characterized by a high number of nucleation sites and no crystallographic preferred orientation. Crystal plastic deformation resulted in high stress heterogeneities close to grain boundaries, even at low bulk strains, inducing a high degree of lattice distortion without significant grain size reduction and the development of a crystallographic preferred orientation. Observed differences in the character of the grain boundary network and internal deformation structures can be explained by significant post-deformation annealing occurring to variable degrees in the carbonado samples. Differences in intensity of crystal bending and subgrain boundary sharpness can be explained by dislocation annihilation and rearrangement, respectively. During annealing grain energy is reduced resulting in distinct changes to the grain boundary geometry. Grain scale numerical modelling shows that anisotropic grain growth, where grain boundary energy is determined by the orientation of a boundary segment relative to the crystallographic orientation of adjacent grains results in straight boundary segments with abrupt changes in orientation even if the boundary is occurring between two triple junctions forming a “zigzag” pattern. In addition, in diamond anisotropic grain growth results in triple junctions that rarely show 120° angles.Our results support the interpretation that carbonados may have undergone at least 2 or 3 stages of development with rapid nucleation, crystal plastic deformation to low strains and variable degrees of post-deformation annealing. Such a history is commonly observed in Earth's crustal or mantle rocks. Hence, for carbonados it is not necessary to invoke an extraordinary and/or extraterrestrial origin and history.The combination of methods utilized here, promises to help advance our understanding of diamond and diamond aggregates in the future.