Change In Crystallographic Orientation Research Articles

Microstructures and Fabric Transitions of Natural Ice from the Styx Glacier, Northern Victoria Land, Antarctica

We investigated the microstructures of five ice core samples from the Styx Glacier, northern Victoria Land, Antarctica. Evidence of dynamic recrystallization was found in all samples: those at 50 m mainly by polygonization, and those at 170 m, largely by grain boundary migration. Crystallographic preferred orientations of all analyzed samples (view from the surface) typically showed a single cluster of c-axes normal to the surface. A girdle intersecting the single cluster occurs at 140–170 m with a tight cluster of a-axes normal to the girdle. We interpret the change of crystallographic preferred orientations (CPOs) at <140 m as relating to a combination of vertical compression, and shear on a horizontal plane, and the girdle CPOs at depths >140 m, as the result of horizontal extension. Based on the data obtained from the ground penetrating radar, the underlying bedrock topography of a nunatak could have generated the extensional stress regime in the study area. The results imply changeable stress regimes that may occur during burial as a result of external kinematic controls, such as an appearance of a small peak in the bedrock.

Hydration of a Mantle Shear Zone Beyond Serpentine Stability: A Possible Link to Microseismicity Along Ultraslow Spreading Ridges?

AbstractHydration of the oceanic mantle is a fundamental process of the global water cycle promoting chemical and volumetric changes and facilitating mantle exhumation along detachment faults. At which depth these processes occur and how fluids circulate along ductile mantle shear zones are, however, less well constrained. Here we present field, chemical, and microstructural evidence of hydration processes of peridotite mylonites within an upper mantle shear zone from an Alpine ophiolite (Lanzo massif, Italy). Mylonitic and ultramylonitic areas of the anastomosing shear zone are enriched in Cl‐bearing amphibole. Electron backscatter diffraction (EBSD) data indicate the activation of the (100)[001] amphibole slip system arguing for synkinematic growth and deformation at temperatures consistent with Mg‐hornblende stability between 800°C and 850°C. High Cl contents in amphibole (0.15–0.61 wt%) as well as oxygen isotope data (δ18Owhole‐rock between 4.4‰ and 4.7‰) indicate accumulation and focusing of seawater‐derived fluid in mylonitic and ultramylonitic domains. Such hydration processes are consistent with strain partitioning between water‐poor (less deformed) and water‐rich (intensely deformed) layers, consistent with changes in olivine and pyroxene crystallographic preferred orientations (CPOs). Our results support recent geophysical data from ultraslow spreading mid‐ocean ridge systems that fluids might penetrate beyond the stability of serpentine to depth between 6 and 15 km. Such peridotite shear zones act as fluid pathways for long‐lived detachment faults or oceanic transform faults, along which upper mantle rocks are exhumed to the seafloor. Fracturing and fluid flow along such peridotite shear zones might be recorded by deep microseismicity along ultraslow spreading ridges.

Micromachining of coarse-grained aluminum including crystallographic effects

This paper presents an experimental analysis of the effects of crystallographic anisotropy of the workpiece material when machining coarse-grained pure aluminum under varying cutting conditions. Orthogonal cutting experiments were conducted on an instrumented planning setup, and cutting forces and surface roughnesses were measured in a full-factorial experimental design. Cutting speed, uncut chip thickness (feed), and tool rake angle were varied at multiple levels. To determine the effect of subsurface deformation left by the previous tool passes, experiments were conducted both with and without cleanup cuts that reduce the surface deformation. The effect of crystallographic orientations and their interaction with cutting conditions on the specific cutting energy, the effective coefficient of friction, and the resulting surface roughness were analyzed through an analysis of variance approach. It was concluded that the crystallographic anisotropy has a strong effect in specific cutting energies, with up to 360% variation across different grains. Similarly, the roughness of the machined surface was seen to vary significantly (up to 831%) with the crystallographic orientations. On the other hand, the effective coefficient of friction was observed to be insensitive to the changes in crystallographic orientations. Lastly, a significant (up to 45%) difference in specific cutting energies was observed between the cases with and without cleanup cuts, indicating the strong presence and the influence of sub-surface deformation.

Dark-field X-ray microscopy reveals mosaicity and strain gradients across sub-surface TiC and TiN particles in steel matrix composites

Residual strain gradients and crystallographic mosaicity across embedded ceramic particles within metal-matrix composites have remained experimentally inaccessible. In this work, we use synchrotron dark-field X-ray microscopy to characterize strain and orientation gradients across ~20 µm large TiC and TiN particles embedded in a steel matrix annealed at 480 and 600 °C. The results document gradual crystallographic orientation changes across the particles and the presence of sub-grains, in contrast to electron backscatter diffraction data. These gradients appear, however, not directly correlated with the observed strain gradients, which are attributed mainly to the different strain states within particles’ interiors and envelopes.

Micromachining Imposed Subsurface Plastic Deformation in Single-Crystal Aluminum

In this work, we analyzed the nature and extent of deformation beneath the machined surface during orthogonal micromachining of single-crystal aluminum. We micromachined six different crystallographic orientations of a sample with [111] zone-axis and analyzed the sub-surface texture and resulting misorientations. The results indicate that the changes in crystallographic orientation induces variations in the depth of deformation, the degree of grain refinement and the lattice rotations. We observed up to 50% lattice rotations, shear bands varying from 55o to 60o from the direction of machining, and highly entangled dislocations, which confirmed the presence of strain hardening.

Mechanism of shear band formation and dynamic softening in a two-phase (α2 + γ) titanium aluminide

Abstract

Electronic structure of AlFeN films exhibiting crystallographic orientation change from c- to a-axis with Fe concentrations and annealing effect

Wurtzite AlN film is a promising material for deep ultraviolet light-emitting diodes. However, some properties that attribute to its crystal orientation, i.e., c-axis orientation, are obstacles in realizing high efficiency devices. Constructing devices with non-c-axis oriented films is a solution to this problem; however, achieving it with conventional growth techniques is difficult. Recently, we succeeded in growing a-axis oriented wurtzite heavily Fe-doped AlN (AlFeN) films via sputtering. In this article, we report the electronic structures of AlFeN films investigated using soft X-ray spectroscopies. As-grown films were found to have conduction and valence band structures for a film with c-axis in film planes. Simultaneously, it was found that large gap states were formed via N-p and Fe-d hybridization. To remove the gap states, the films were annealed, thereby resulting in a drastic decrease of the gap states while maintaining a-axis orientation. We offer heavy Fe-doping and post annealing as a new technique to obtain non-polar AlN films.

Influence of VIP treatment modes on nitride coatings formation with different crystallographic orientation

The change in crystallographic orientation during nitride coatings formation based on titanium and zirconium is studied depending on changes in the concentration ratios for the gas and metal components of the plasma flows and their energy effects on the treated substrate during vacuum ion-plasma (VIP) treatment. It is shown that a decrease in the interaction energy of the gas-metal plasma flow with the surface contributes to the transition of the texture formation of the phase composition to the non-texture.

Effect of pre-compression on changes in texture and yielding behavior of ZK61 Mg alloy

The bimodal grained, strong basal textured extruded ZK61-T4 magnesium alloy was successfully achieved by solution heat treatment at 510 °C for 3 h {10–12} twin is preferentially operative by the compression of c-axis of hexagonal closed pack crystal structure in strong basal textured magnesium alloys and results in low yield strength. Pre-compression is a convenient technique for re-assigning the crystallographic orientations and introducing the different twins systems. Twins in pre-compressed ZK61-1 and ZK61-2 alloys cause grain refinement hardening effect and the crystallographic orientation changes greatly from strong basal texture to weak basal texture, which leads to a remarkable increase in yield strength. The strength of the pre-compressed specimens shows an improvement in YS ~63.52% along normal direction, ~25.89% along extruded direction and ~107.41% along transverse direction of ZK61-1 alloy, while ~22.04% along normal direction, ~54.04% along extruded direction and ~91.79% along transverse direction of ZK61-2 alloy in comparison of ZK61-T4 alloy.

Characterization of spark plasma sintered TiN nanoparticle strengthened titanium alloy using EBSD and TKD

Spark plasma sintering is one of the best fabrication techniques for producing products with little grain growth and control of microstructures. Ti6Al4V alloy strengthened with 4 vol.% TiN was produced by spark plasma sintering method. In this study, the influence of nanoparticle ceramic addition, dispersion behaviour and interfaces reaction existence on the sintered titanium matrix composite were investigated. The microstructural characterization of the sintered composite was analyzed using scanning electron microscopy (FE-SEM) with an attachment of electron backscatter diffraction (EBSD), transmission Kikuchi diffraction (TKD) and X-ray diffraction (XRD) technique for phases identification. The results show that TiN nanoparticle was evenly dispersed in the sintered composite which resulted in the formation of grains with changes in crystallographic orientations after the addition of nanoparticle material. Moreover, the TKD attempt has been made to reveal TiN interface sub-grains structures formed at the grain boundary during the process of spark plasma sintering.

Investigation of Grain Refinement Mechanism of Nickel Single Crystal during High Pressure Torsion by Crystal Plasticity Modeling.

The excellent properties of ultra-fine grained (UFG) materials are relevant to substantial grain refinement and the corresponding induced small grains delineated by high-angle grain boundaries. The present study aims to understand the grain refinement mechanism by examining the nickel single crystal processed by high pressure torsion (HPT), a severe plastic deformation method to produce UFG materials based upon crystal plasticity finite element (CPFEM) simulations. The predicted grain maps by the developed CPFEM model are capable of capturing the prominent characteristics associated with grain refinement in HPT. The evolution of the orientation of structural elements and the rotations of crystal lattices during the HPT process of the detected differently oriented grains are extensively examined. It has been found that there are mainly two intrinsic origins of lattice rotation which cause the initial single crystal to subdivide. The correlation between the crystallographic orientation changes and lattice rotations with the grain fragmentation are analyzed and discussed in detail based on the theory of crystal plasticity.

Evolution of structural and morphological characteristics of MoS2 thin films with nitrogen doping

The two-dimensional MoS2 coatings with incomplete head triangles, triangular stars and six-blade stars domain shape have been grown by the CVD method on SiO2/Si and Si substrates and then doped with nitrogen. The shape of MoS2 domains showed remarkable changes after N2 doping. Doping dramatically changed the physical properties of MoS2 coatings. An accurate study was carried out on the prepared MoS2 thin films using optical microscopy, atomic force microscopy (AFM), X-ray diffraction (XRD) and Raman spectroscopy. The X-ray spectrum showed well-defined MoS2 coatings with a strong (103) preferred orientation of a typical hexagonal structure. There were no changes in crystallographic orientations after nitrogen doping, while the peak intensity declined. Raman spectroscopy specified that MoS2 multilayer was proved by Raman frequency difference between two characteristic modes (E 2g 1 and A1g). The position and intensity of Raman modes exhibited sensitivity to nitrogen doping. The AFM results indicated topography and roughness variations with nitrogen doping.

Voltage-Controlled Bistable Thermal Conductivity in Suspended Ferroelectric Thin-Film Membranes.

Ferroelastic domain walls in ferroelectric materials possess two properties that are known to affect phonon transport: a change in crystallographic orientation and a lattice strain. Changing populations and spacing of nanoscale-spaced ferroelastic domain walls lead to the manipulation of phonon-scattering rates, enabling the control of thermal conduction at ambient temperatures. In the present work, lead zirconate titanate (PZT) thin-film membrane structures were fabricated to reduce mechanical clamping to the substrate and enable a subsequent increase in the ferroelastic domain wall mobility. Under application of an electric field, the thermal conductivity of PZT increases abruptly at ∼100 kV/cm by ∼13% owing to a reduction in the number of phonon-scattering domain walls in the thermal conduction path. The thermal conductivity modulation is rapid, repeatable, and discrete, resulting in a bistable state or a "digital" modulation scheme. The modulation of thermal conductivity due to changes in domain wall configuration is supported by polarization-field, mechanical stiffness, and in situ microdiffraction experiments. This work opens a path toward a new means to control phonons and phonon-mediated energy in a digital manner at room temperature using only an electric field.

Superhard CrN/MoN coatings with multilayer architecture

Main regularities of the formation of microstructure and properties of multilayer nanostructured CrN/MoN films with periodically changing architecture of layers were considered. Coatings were fabricated by vacuum-arc evaporation of the cathodes (Arc-PVD) in nitrogen atmosphere (pN was 0.4, 0.09 and 0.03 Pa). CrN and γ-Mo2N nitride phases with fcc lattices and a small volume of metastable MoNx cubic phase were formed in the films at pN = 0.4 Pa. The decrease of pN to 0.09 Pa causes the formation of β-Cr2N hexagonal phase. Preferential crystallographic orientation changes from [311] to [111] and [200] when bias voltage Ub is −20, −150 and −300 V respectively. The nanocrystallites size in coatings with bilayer thickness λ = 44 nm decreases to 5.8 nm. The microdeformation grows from 0.4 to 2.3% when Ub changes to −20 V. Coatings show high hardness of 38–42 GPa and H/E = 0.107. In a couple with results of tribological tests, coatings demonstrate strong wear resistance, which makes them appropriate and promising for industrial applications as protective ones. The effect of deposition conditions (pN, Ub, λ) on composition, structure, hardness, toughness and wear resistance was studied to achieve superior mechanical and physical properties of coatings with long lifetime in harsh environment.

Controllable formation of MoS2 via preferred crystallographic orientation modulation of DC-sputtered Mo thin film

In this letter, we report the effects of preferred crystallographic orientation of Mo films on the formation of MoS2 layer through elemental sulphurization process. Vacuum thermal annealing of as-sputtered Mo films results in noticeable change in preferred crystallographic orientation from (1 1 0) to (2 1 1) plane. Correlation between structural and Raman spectroscopy study indicates that Mo film with predominantly (2 1 1) orientation results in pronounced formation of MoS2 compared to the film with the higher degree of (1 1 0) orientation. Planar packing factor, which depends on crystallographic orientation is proposed to play a crucial role in determining the degree of MoS2 formation.

Domain-engineered BiFeO3 thin-film photoanodes for highly enhanced ferroelectric solar water splitting

In photoelectrochemical (PEC) water splitting, charge separation and collection by the electric field in the photoactive material are the most important factors for improved conversion efficiency. Hence, ferroelectric oxides, in which electrons are the majority carriers, are considered promising photoanode materials because their high built-in potential, provided by their spontaneous polarization, can significantly enhance the separation and drift of photogenerated carriers. In this regard, the PEC properties of BiFeO3 thin-film photoanodes with different crystallographic orientations and consequent ferroelectric domain structures are investigated. As the crystallographic orientation changes from (001)pc via (110)pc to (111)pc, the ferroelastic domains in epitaxial BiFeO3 thin films become mono-variant and the spontaneous polarization levels increase to 110 μC/cm2. Consequently, the photocurrent density at 0 V vs. Ag/AgCl increases approximately 5.3-fold and the onset potential decreases by 0.180 V in the downward polarization state. It is further demonstrated that ferroelectric switching in the (111)pc BiFeO3 thin-film photoanode leads to an approximate change of 8,000% in the photocurrent density and a 0.330 V shift in the onset potential. This study strongly suggests that domain-engineered ferroelectric materials can be used as effective charge separation and collection layers for efficient solar water-splitting photoanodes.

The influence of melt flow on grain structure of tin and its alloys produced by ultrafast quenching from the melt

The results on the grain structure and texture of tin and tin-based foils produced by ultrafast quenching from the melt are presented in this work. The formation of fine equiaxed and large grains elongated along the spreading direction of the foil was observed. Detailed studies of subgrain structure showed that the crystallographic orientation of elongated grains changes monotonically within the grain. It can be assumed that the reason for the change of crystallographic orientation is the deformation of solidified material. The deformation is caused by the viscous force of undercooled melt which moves above the crystallization front in the direction of the foil spreading.

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.

Microstructural and crystallographic response of shock-loaded pure copper

Abstract

Combined size and texture-dependent deformation and strengthening mechanisms in Zr/Nb nano-multilayers

A combination of transmission electron microscopy analyses and nanomechanical measurements was performed in this study to reveal deformation and strengthening mechanisms occurring in sputtered Zr/Nb nanoscale metallic multilayers (NMMs) with a periodicity (L) in the range 6–167 nm. Electron diffraction analyses revealed a change in the crystallographic orientation of α-Zr when L≤27 nm, while Nb structure retained the same orientations regardless of L. For L > 60 nm, the strengthening mechanism is well described by the Hall-Petch model, while for 27 < L < 60 nm the refined CLS model comes into picture. A decrease in strength is found for L < 27 nm, which could not be simply explained by considering only misfit and Koehler stresses. For L≤27 nm, plastic strain measured across compressed NMMs revealed a change in the plastic behaviour of α-Zr, which experienced a hard-to-soft transition. At these length scales, the combination of two structural factors was found to affect the strength. These relate to the formation of weaker interfaces which extend the effective distance between strong barriers against dislocation transmission, thus producing a softening effect. The second effect relates to the crystallographic orientation change exhibited by α-Zr for L<27 nm with a consequent change of the dominant slip system. The actual strength at these smaller length scales was effectively quantified by taking these structural aspects into account in the interface barrier strength model.