Crystallographic Preferred Orientation Research Articles

The anisotropy of geomaterial granite

Abstract. Granites appear to be isotropic, which qualifies them as suitable crystalline host rocks for nuclear waste repository sites. However, despite their optical appearance, granites show a primary structural anisotropy (Bouchez, 1997) that evolved during emplacement and crystallization of the melt. The major processes involved are magmatic flow and oriented crystal growth (Müller et al., 2011). Hypothetically, it is expected that different tectonic environments, i.e. different orientations of the stress tensor, cause significant differences in the primary anisotropy, which is expressed by the crystallographic preferred orientation (CPO) of the rock-forming minerals. It is likely that primary anisotropic petrophysical properties control the orientation of post-magmatic structural features like extensional fractures and thus shape potential fluid pathways. We present the first results of a systematic study of felsic plutonites, i.e. the GAME project (Gefüge, Textur- und Anisotropie-Messungen von potenziell für die Endlagerung geeigneten Graniten zur Charakterisierung möglicher Fluidwegsamkeiten). The samples of syn-Variscan felsic plutons from two sites (Erzgebirge and Fichtelgebirge) represent different tectonic settings during intrusion: extension and compression. Furthermore, they depict different stages of fractionation of the peraluminous granite suites. The CPOs were analysed using the neutron time-of-flight (ToF) texture diffractometer SKAT (Keppler et al., 2014; Ullemeyer et al., 1998) and EBSD (electron backscatter diffraction). Using scanning electron microscope (SEM) automated mineral liberation analysis (Schulz et al., 2020), modal mineral compositions are quantified. This enables us to model primary or “intrinsic” petrophysical properties for these granites based on the elastic stiffness tensor of the individual rock-forming minerals (Mainprice et al., 2011). Main- and trace-element geochemical data (ICP-AES and ICP-MS) allow for a characterization of the different magmatic settings of the samples. All granites show distinct preferred orientations of rock-forming minerals. The quartz textures, for example, exhibit similar CPOs, with point maxima of the positive rhombs in combination with small circles to crossed-girdle c-axis distributions. However, the orientation with respect to the geographic reference system strongly varies. We will discuss the CPOs in relation to the stress tensor orientation during emplacement of the felsic plutons and compare the primary anisotropy with the post-magmatic fracture patterns of the particular granites.

Nanostructure Control in Zinc Oxide Films and Microfibers through Bioinspired Synthesis of Liquid-Crystalline Zinc Hydroxide Carbonate; Formation of Free-Standing Materials in Centimeter-Level Lengths.

Free-standing zinc oxide in the forms of films and fibrous materials are expected to be used as functional devices such as piezoelectric devices and catalyst filters without being limited by the growth substrate. Herein, a synthetic morphology-control method for 2D and 1D free-standing ZnO materials with ordered and nanoporous structures by conversion of liquid-crystalline (LC) zinc hydroxide carbonate (ZHC) nanoplates is reported. As a new colloidal liquid crystal, the LC ZHC nanoplate precursors are obtained by a biomineralization-inspired method. The approach is to control the morphology and crystallographic orientation of ZHC crystals by using acidic macromolecules. Their nano-scale and oriented structures are examined. The LC oriented ZHC nanoplates have led to the synthesis of free-standing films and microfibers of ZHC in centimeter-level lengths, with the successful thermal conversion into free-standing films and microfibers of ZnO. The resultant ZnO films and ZnO microfibers have nanoporous structures and preferential crystallographic orientations that preserve the alignment of ZHC nanoplates before conversion.

Melt Network Reorientation and Crystallographic Preferred Orientation Development in Sheared Partially Molten Rocks

AbstractWe investigated the co‐evolution of melt, shape, and crystallographic preferred orientations (MPOs, SPOs, and CPOs) in experimentally deformed partially molten rocks, from which we calculated the influence of MPO and CPO on seismic anisotropy. Olivine‐basalt aggregates containing 2 to 4 wt% melt were deformed in general shear at a temperature of 1,250°C under a confining pressure of 300 MPa at shear stresses of τ ≤ 175 MPa to shear strains of γ ≤ 2.3. Grain‐scale melt pockets developed a MPO parallel to the loading direction by γ < 0.4. At higher strains, the grain‐scale MPO remained parallel to the loading direction, while incipient sample‐scale melt bands formed at ∼20° to the grain‐scale MPO. An initial SPO and CPO were induced during sample preparation, with [100] and [001] axes girdled perpendicular to the long axis of the starting material. At the highest explored strain, a strong SPO was established subperpendicular to the loading direction, and the [100] axes of the CPO clustered nearly parallel to the shear plane. Our results demonstrate that grain‐scale and sample‐scale alignments of melt pockets are distinct. Furthermore, the melt and the solid microstructures evolve on different timescales: in planetary bodies, changes in the stress field will drive a relatively fast reorientation of the melt network and a relatively slow realignment of the crystallographic axes. Rapid changes to seismic anisotropy in a deforming partially molten aggregate are thus caused by MPO rather than CPO.

Electrodeposition of Ni-Fe-Co and Ni-Fe Graphene Oxide Alloy Composites

Graphene platelets can impart unique properties to metal matrices, such as enhanced conductivity, mechanical, thermal properties and catalytic activity.1,2 The electrodeposited process to fabricate composite metal matrices has an advantage over other techniques because it can avoid high heat treatment and deformation during fabrication, which can damage the intrinsic structure of graphene plates. Graphene itself is difficult to disperse and incorporate into electrodeposited films, but the oxidized form, having abundant surface functional groups, can be readily dispersed into aqueous solutions. Examples of electrodeposited metals with included graphene oxide (GO) from the electrolyte include elemental deposits such as Ni,3-4 Cu,2,5-6 and Co.7,8 In these studies, graphene oxide addition to the metal matrices promoted enhanced thermal conductivity in Cu,6 grain refinement in Ni4 and Cu5, improved wear resistance of Co7,8 and in the case of Ni changed its preferred crystallographic orientation.3 In alloy electrodeposition, the particle in the electrolyte may also alter the deposit composition through disparate changes in the individual metal ion partial current densities. The alloys containing Fe, Ni and Co from the reduction of their metal ions are of interest for their peculiar behavior, where there tends to be an inhibition of the more noble species reduction reaction (e.g. Ni, Co) in favor of the less noble (Fe) referred to as anomalous codeposition.9 To examine the influence of graphene oxide on the deposit composition, Ni-Fe-Co alloys were galvanostatically electrodeposited from a boric acid-sulfamate electrolyte containing commercial graphene oxide plates. Rotating disk electrodes were used to control the hydrodynamic environment near the cathode. The composition, morphology and structure were examined. The addition of graphene oxide resulted in a change in deposit composition, particularly for Fe and Ni, at low cathodic current densities less than 50 mA/cm2, with the deposit becoming less anomalous with the addition of graphene oxide. The change in composition is thought to be derived from a decrease in adsorbed iron intermediates from an anomalous codeposition model. The partial current densities of Ni-Fe-Co deposition with a measure of ohmically corrected potential are compared with Ni-Fe, Ni and Fe deposition with graphene. References H.G. P. Kumar, M. A.Xavior, Procedia Eng. 97 1033 (2014).J. Biswal, P. R. Vundavilli, and A. Gupt, J. Electrochem. Soc., 167 146501 (2020).D. Kuang, L. Xu, L. Liu, W. Hu, Y. Wu, Appl. Surf. Sci., 273, 484 (2013).J. Li, Z. An, Z. Wang, M. Toda, and T. Ono, ACS Appl. Mater. Interfaces, 8, 3969 (2016). L. P. Pavithra, B. V. Sarada, K. V. Rajulapati, T, N. Rao and G. Sundararajan, Nature Sci Rep 4, 4049 (2014).K. Jagannadham, Metall. Mater. Trans B 43 B 316 (2012).C. Liu, F. Su, J. Liang, Appl. Surf. Sci. 351 889 (2015).A. Toosinezhad, M. Alinezhadfar, S. Mahdavi, Ceram. Int., 46, 16886 (2020).A. Brenner, Electrodeposition of Alloys: Principles and Practice, Academic Press Inc., New York, pp. 399-450 (1963).

Grain growth of natural and synthetic ice at 0 °C

Abstract. Grain growth can modify the microstructure of natural ice, including the grain size and crystallographic preferred orientation (CPO). To better understand grain-growth processes and kinetics, we compared microstructural data from synthetic and natural ice samples of similar starting grain sizes that were annealed at the solidus temperature (0 ∘C) for durations of a few hours to 33 d. The synthetic ice has a homogeneous initial microstructure characterized by polygonal grains, little intragranular distortion, few bubbles, and a near-random CPO. The natural ice samples were subsampled from ice cores acquired from the Priestley Glacier, Antarctica. This natural ice has a heterogeneous microstructure characterized by a considerable number of air bubbles, widespread intragranular distortion, and a CPO. During annealing, the average grain size of the natural ice barely changes, whereas the average grain size of the synthetic ice gradually increases. These observations demonstrate that grain growth in natural ice can be much slower than in synthetic ice and therefore that the grain-growth law derived from synthetic ice cannot be directly applied to estimate the grain-size evolution in natural ice with a different microstructure. The microstructure of natural ice is characterized by many bubbles that pin grain boundaries. Previous studies suggest that bubble pinning provides a resisting force that reduces the effective driving force of grain-boundary migration and is therefore linked to the inhibition of grain growth observed in natural ice. As annealing progresses, the number density (number per unit area) of bubbles on grain boundaries in the natural ice decreases, whilst the number density of bubbles in the grain interiors increases. This observation indicates that some grain boundaries sweep through bubbles, which should weaken the pinning effect and thus reduce the resisting force for grain-boundary migration. Some of the Priestley ice grains become abnormally large during annealing. We speculate that the contrast of dislocation density amongst neighbouring grains, which favours the selected growth of grains with low dislocation densities, and bubble pinning, which inhibits grain growth, are tightly associated with abnormal grain growth. The upper 10 m of the Priestley ice core has a weaker CPO and better-developed second maximum than deeper samples. The similarity of this difference to the changes observed in annealing experiments suggests that abnormal grain growth may have occurred in the upper 10 m of the Priestley Glacier during summer warming.

Interseismic creep of carbonate-hosted seismogenic normal faults: Insights from central Italy

Understanding fault behavior in carbonates is critical because they represent loci of earthquake nucleation. Models of fault-slip mode generally assume: (1) seismic sliding and aseismic sliding occur in different fault patches, (2) creep is restricted to lithology-controlled weak domains, and (3) rate-weakening patches are interseismically locked. We studied three carbonate-hosted seismogenic normal faults in central Italy by combining (micro)structural and geochemical analyses of fault rocks integrated with new seismic coupling estimates. The (upper bound) seismic coupling was estimated to be ∼0.75, which indicates that at least 25% of the long-term deformation in the study area is released aseismically in the upper crust. Microscopy and electron-backscatter diffraction analyses revealed that whereas the localized principal slip zone records seismic slip (as ultracataclastic material, calcite crystallographic preferred orientation (CPO), and truncated clasts), the bulk fault rock below behaves differently. Cataclasites in massive limestones deform by cataclastic flow, pressure solution, and crystal plasticity, along with CPO development. Foliated tectonites in micritic limestones deform by pressure solution and frictional sliding, with CPO development. We suggest these mechanisms accommodate on-fault interseismic creep. This is consistent with experimental results reporting velocity-strengthening behavior at low slip rates. We present multiscale evidence of coexisting seismic and aseismic slip along the same fault in limestones during the seismic cycle. Our results imply that on-fault aseismic motion must be added to seismic slip to reconcile the long-term deformation rates and that creep is not exclusive to phyllosilicate-bearing units. Our work constitutes a step forward in understanding fault behavior and the seismic cycle in carbonates, and it may profoundly impact future studies on seismogenic potential and earthquake hazard assessment.

Creep deformation and damage characteristics of nickel-based superalloy GH4169

To further understand the creep behavior of nickel-based superalloys, creep deformation and damage characteristics of nickel-based superalloy GH4169 were investigated systematically by using SEM, EBSD and TEM characterizations in this study. Creep tests were conducted at 650 °C under 820 MPa.The results indicated that the fractions of low-, high-angle, and twin grain boundaries changed significantly after creep. Due to the grain rotation mechanism, the overall microstructure changed from random to preferred crystallographic orientation. <110>//loading direction (LD) oriented grains were rotated to <100>//LD and <111>//LD fibers, resulting in the decrease of <110> fiber, and the increase of <100> and <111> fibers. Cases of <110> oriented grains rotating into <100> and <111> orientations were also provided. Deformation twin and stacking faults were determined as the main deformation mechanisms. The failure of the specimen was induced by intergranular brittle fracture. The grain boundaries with special characteristics, namely high Schmid factor m and low Schmid factor mismatch Δm of neighbouring grains, and low geometric compatibility factor m’, exhibited high susceptibility to cracking.

Effects of solution treatment on microstructure and mechanical properties of (SiC+TiB2)/Al–Zn–Mg–Cu composite fabricated by laser powder bed fusion

This study investigated the effects of solution treatment (ST) on the microstructure and mechanical properties of (SiC+TiB2)/Al–Zn–Mg–Cu composite produced using laser powder bed fusion (LPBF). Microstructural analysis reveals that the grid-like distribution of eutectic precipitates within the as-printed composite disappeared, giving way to the formation of uniformly distributed precipitates. As the ST temperature increased, the content of spherical Si particles decreased, while the content of elongated Al4SiC4 precipitates increased. Matrix grains recrystallization occurred, resulting in a gradual increase in the average grain size from 3.79 μm to 5.23 μm. The preferred crystallographic orientation features along the printing direction, <001> {001} plate texture, were weakened, gradually exhibiting a more disordered growth. The microhardness and tensile strength of the composites exhibited a slight decrease and exhibited a trend of initially increasing and then decreasing with increasing ST temperature. Additionally, the heterogeneity in microhardness along different directions has been reduced. When the ST temperature was 460 °C, the elongation of the composite experienced a significant increase, escalating from 6.12 ± 0.36% to 10.3 ± 0.25%. However, with the increase in ST temperature, it displayed an obvious downward trend. The maximum tensile strength was 449 ± 8 MPa, and the elongation was 9.6 ± 0.4% with the ST temperature of 500 °C. The variations in mechanical properties were primarily attributed to the elimination of grid-like substructure, the uniform distribution of precipitates, and the gradual coarsening of grains. This research was expected to contribute to developing advanced lightweight materials with improved performance, opening up new opportunities for their application in various industries.

The water-poor and reduced mantle beneath the Neo-Tethys Ocean: Tectonic setting of the western Yarlung-Tsangpo ophiolites

Water contents and deformation behaviors of minerals in mantle peridotites are diagnostic features to distinguish the physical conditions between mid-ocean ridges and subduction zones, which could serve as effective indicators for discriminating the tectonic setting of ophiolites. In this study, we report a systematic dataset of petrology, geochemistry, water contents and deformation behaviors for the mantle peridotites from the Cuobuzha ophiolite in the western Yarlung-Tsangpo suture zone (YTSZ), southern Tibet, to provide new insights into the long-standing debate for the tectonic setting of ophiolites therein. Geochemical data revealed that the Cuobuzha mantle peridotites experienced low to moderate degrees of partial melting (∼10–15%), although some harzburgites have been intensively modified by late-stage melt-rock interactions. The Cuobuzha peridotites, on the other hand, are characterized by low orthopyroxene water contents (46–95 wt ppm in average), clear olivine crystallographic preferred orientations of A- and E-types, and low oxygen fugacity (logfO2, QFM −2.55 to −0.81, where QFM means quartz-magnetite-fayalite buffer), thus indicative of the occurrence of high-temperature, water-depleted, and reduced mantle in this ophiolite. The features above of the Cuobuzha mantle peridotites are quite similar to those of abyssal peridotites at modern mid-ocean ridges and systematically different from the relatively refractory, water-rich, and oxidized characteristics typical of forearc peridotites in suprasubduction zones. Based on the data from this study and a compiled dataset for other ophiolites from the western YTSZ, we revealed that mantle peridotites with a water-poor and reduced nature are common in these ophiolites, thus providing strong evidence supporting for their origination from a mid-ocean ridge of a mature ocean basin. From the perspective of mantle peridotites, the ophiolites in the western YTSZ now geographically distributed in two branches (i.e., the northern and southern sub-belts) might have formed in a single ocean basin of the Neo-Tethys and were dismembered by late-stage tectonic events to their current locations.

“In-plane” site-specific FIB lamella extraction from deformed magnetite and the investigation of low angle grain boundaries under TEM

In this study a modus operandi to investigate site-specific nanostructures in thin films (lamellae) excavated “in-plane” across (sub)grain boundaries is presented. This is done by discussing the case of a magnetite grain hosted in a thin section of banded iron formation (Norway) that is prepared parallel to the kinematic reference frame (XZ section of the strain ellipsoid). SEM-EBSD analysis reveal that the magnetite grains do not develop a strong crystallographic preferred orientation, although individual grains are strained and show evidence of intracrystalline deformation in form of low angle grain boundaries (LAGB's). Two “in-plane” lamellae using focused ion beam (FIB) technique are excavated from a magnetite grain in the kinematic reference frame, and nanostructures are studied along three LAGB's using high resolution transmission electron microscopy imaging followed by Fourier transformation (FT), inverse FT and estimation of dislocation densities. Our data establish an empirical relationship for the studied LAGBs, namely, the smaller the angle between LAGB and X-direction, the larger are the shear strain and dislocation density. This relationship is validated from numerical simulations of viscoplastic deformation and dynamic recrystallisation of polycrystalline aggregates of halite, which is also a cubic mineral analogous to magnetite. In addition to the site-specific “in-plane” FIB lamella information, this study also shows that in a deformed mineral the different orientations of the LAGB compared to the principal strain axes show a different dislocation density. This approach of full tracking of the extension direction (X) from the macroscopic to the nano-scale could play an important role in forward modelling of microstructure evolution in future studies.

Microfabric evolution during metasomatism and deformation, exemplified by the nodular sillimanite gneisses (Bamble lithotectonic domain, South Norway)

Proterozoic foliated and nodular sillimanite gneisses from the Bamble lithotectonic domain, South Norway, are analysed to unravel their microfabric evolution with mineral reactions during metasomatism and associated deformation. The nodules form cm-scaled spherical to ellipsoidal sillimanite-quartz aggregates that locally grade into foliated sillimanite gneisses. Independent on their fabric, they record incomplete breakdown reactions of biotite and K-feldspar recorded by muscovite lamellae and associated Fe-oxide needles in biotite and by muscovite-quartz aggregates after K-feldspar. Muscovite is partly replaced by sillimanite. Based on immobile Al, the nodular gneiss forming reactions give excess K, Mg and H2O that may leave the nodular gneiss to form a metasomatic agent and caused regional metasomatism (scapolitisation) in the surrounding rocks. Quartz in the foliated gneisses shows a pronounced shape but no marked crystallographic preferred orientation. There is no indication of major strain accumulation by quartz dislocation creep. Muscovite shows lobate phase boundaries to quartz, which is interpreted as reaction fabric, from the breakdown reactions of K-feldspar and biotite. The nodular and sillimanite gneisses formed during metasomatic mineral reactions, where major elements K, Mg and H2O leave the rock and an Al-rich metasomatic restite remains. We suggest that the metasomatism involved a molar volume loss, where reactions forming muscovite, quartz and sillimanite occurred by incongruent dissolution-precipitation creep at low stresses forming the nodular and foliated gneisses. Our study demonstrates that metasomatism with chemical rock changes and mass transfer associated with incongruent dissolution-precipitation contributed to the observed reaction and deformation microfabric.

Second harmonic generation and two photon absorption assisted power limiting mechanism of l-Phenylalanine (LPA) - poly-ethylene-oxide (PEO) electrospun nanofibers

Nanofibers consisting of organic nonlinear optical l-Phenylalanine (LPA) nanocrystals embedded in poly-ethylene-oxide (PEO) polymer were synthesized by the electrospinning technique. The preferred crystallographic orientation of the organic molecules that crystallized inside the nanofibers was demonstrated through X-ray diffraction and calculations show that the average crystallite size is around 28 nm. SEM images clearly show the formation of smooth fibers with average diameter of 246 nm. The emission of green light from the nanofiber powder sample approved the second harmonic generation (SHG) under the excitation of Nd: YAG laser (1064 nm). Further the generation of second harmonic from the fibers was confirmed by nonlinear microscope imaging and power dependent SHG studies, performed using femtosecond fiber laser (1040 nm). The nonlinear absorption and its power limiting characteristics of LPA-PEO electro-spun nanofibers were studied utilizing the Z-scan method employing Q switched Nd: YAG laser as an excitation source (532 nm, 5 ns, 10 Hz). Open aperture Z-scan measurement (with intensity 1.23 × 1012 W/m2 and 2.4623 × 1012 W/m2) revealed the reverse saturable absorption property of LPA-PEO nanofibers. The existence of a sequential two-photon absorption process involving real resonant intermediate states has been demonstrated by the intensity dependent two-photon absorption coefficient. The usefulness of LPA optical fibers as power limiters is ensured by their lower optical limiting threshold than other optical limiting materials.

Microstructural Insights into the Evolution of Ophiolitic Chromite from Luobusha

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

Laser powder bed fusion of GH3536 nickel-based superalloys: Processing parameters, microstructure and mechanical properties

In this study, a GH3536 nickel-based superalloys was fabricated by the laser powder bed fusion technology (LPBF) with emphasis on its microstructure evolution and mechanical properties. Nearly fully dense specimens with the relative density of about 98.8% were obtained by parameter optimization. GH3536 nickel-based superalloys swirlers based on the optimized processing parameters show a high surface finish and no obvious macro-defects are observed. An excellent strength–ductility balance of the alloy with a yield strength of 675 MPa, an ultimate tensile strength of 823 MPa and an elongation of 22.3% was attained. The TEM results show the significant micro segregation of Mo and Cr at columnar sub-grain boundaries and promoted the formation of the chain-like carbides, improving the room temperature strength. The grains of the specimens show obvious bimodal grain structure and the crystals have a preferred crystallographic orientation along 〈001〉 direction and the texture orientations were fiber 〈100〉 and {001} 〈310〉. These findings provide some guidance for the industrial application of LPBF manufacturing high-quality GH3536 nickel-based superalloys components.

Twinning microstructure in the solid-phase epitaxial crystallization of BaTiO3

Amorphous BaTiO3 layers deposited on SrTiO3 (001) substrates at room temperature were subsequently crystallized using solid phase epitaxy (SPE). Heating an initially amorphous BaTiO3 layer in air at 650 °C for 3 h resulted in crystallization with components in two distinct crystallographic orientation relationships with respect to the substrate. Part of the volume of the BaTiO3 layer crystallized in a cube-on-cube relationship with the substrate. Other volumes crystallized in four variants of a 70.5° rotation about ⟨110⟩, resulting in a ⟨221⟩ surface normal in each case. Each of these four variants forms a Σ = 3 coincident site lattice with respect to the SrTiO3 substrate and the cube-on-cube oriented BaTiO3. Heating for the same duration and temperature in a reducing gas atmosphere resulted in the formation of polycrystalline BaTiO3 with no preferred crystallographic orientation. The dependence on the gas atmosphere indicates that it may be possible to tune the annealing time, temperature, and atmosphere to produce a single crystalline BTO on STO by SPE or produce a desired distribution of orientations.

Erosion Performance of TiAlSiN Coatings Prepared by High-Power Pulsed Magnetron Sputtering

Erosion seriously threatens the safety of high-speed rotating mechanical components in very harsh service environments, particularly for lightweight titanium alloy matrix material. In order to improve the erosion resistance of titanium alloy, TiAlSiN coatings with different phase compositions are deposited on TC6 titanium alloy using a high-power pulse magnetron sputtering discharge (HPPMS) system under various discharge voltages. The componential and microstructural evolution as well as mechanical properties of the TiAlSiN coatings are evaluated by X-ray diffraction, scanning electron microscopy, and nanoindentation, respectively. The erosion performance relative to titanium alloy is investigated by a sand blasting tester. With the increase in discharge voltage from −500 to −600 V, the peak of discharge current increases from 105 to 225 A. The prepared TiAlSiN coatings show a shift of the preferred crystallographic orientation from (220) to (200), but all of them have a dense nanocomposite structure. Their hardness (H) and elastic modulus (E) gradually increase before decreasing, arriving at maximum values of 35.34 and 360.5 GPa at −570 V. The erosion resistance of the TiAlSiN coatings dependent on the discharge voltage is consistent with the H/E ratio change. The TiAlSiN coatings prepared at −560 V exhibit the optimal erosion resistance, which is 15 times that of the TC6 substrate. The erosion behavior of the coatings is positively correlated with their hardness and toughness. Adjusting the discharge voltage of the HPPMS pulse is finally proved to be an effective way of tailoring the coating phase compositions to improve the erosion resistance of titanium alloy.

Structural inheritance controlled by olivine viscous anisotropy in fossil mantle shear zones with different past kinematics

Geophysical and geological observations hint for the presence in the lithospheric mantle of both active and fossil shear zones with varied past kinematics. Shear in the lithospheric mantle produces olivine crystallographic preferred orientations (CPO), which lead to dependence of the viscous behavior on the direction of the load. Yet, the role of anisotropic viscosity in the mantle is seldom considered in models of structural reactivation. Here, we present 3-D geodynamic finite-element models that quantify the strain and viscosity distribution in a lithosphere containing a fossil thrust (or extensional) mantle shear zone with variable orientation relatively to a new extensional or compressional tectonics. The results were compared to that of a fossil strike-slip mantle shear zone. The fossil olivine CPO in the shear zone produces an anisotropic response of the lithospheric mantle, which is modelled using a parameterized description of viscous anisotropy derived from polycrystal plasticity simulations. We found that CPO-induced reactivation of fossil extensional or thrust mantle shear zones is favored for dips 30–60°, with maximum strain localization if the load is normal to the trend of a fossil shear zone dipping by 45°-50°. This represents a broader range of reactivation potential than in fossil strike-slip mantle shear zones. Both fossil shear zones trending at 45° to the imposed load are reactivated regardless of their dip. For a given viscous anisotropy in the lithospheric mantle (i.e., fossil shear zone orientation), the associated strain localization in the crust is always higher under extensional reactivation, where strain rates may be up to ∼100 times higher than those in the (isotropic) surrounding crust. These results imply that viscous anisotropy associated with fossil mantle shear zones plays a key role in large-scale structural reactivation during successive tectonic episodes, shaping the current lithospheric architecture, such as in the Pyrenees and Norwegian margin.

Enhancing magnetocaloric properties of NiMnGa-based alloys via Dy micro-alloying and pseudoelastic cyclic training

Considerable interest to improve magnetic entropy change (ΔSm) and broaden working temperature interval (WTI) of NiMnGa ferromagnetic shape memory alloys (FESMAs) was stimulated by their applications as promising candidate materials for solid-state refrigeration. In the present study, we presented an approach to enhance the magnetocaloric properties of polycrystalline NiMnGa FESMAs via combining Dy micro-alloying and pseudoelastic cyclic training. The introduction of Dy elements established stable magneto-structural coupling transformation from the paramagnetic austenite to ferromagnetic martensite, accompanied by a large ΔSm [−16.42 J/(kg K)] and a widened WTI (∼15.98 K). Fascinatingly, it was demonstrated that the internal strain fields at phase interface between matrix and DyNi4Ga precipitates could assist the phase transformation nucleation, which significantly reduced the hysteresis loss from 20.84 J/kg of Ni54Mn25Ga21 alloy to 8.14 J/kg of Ni54Mn25Ga20.7Dy0.3 alloy. More importantly, the subsequent pseudoelastic cyclic training produced a strong ⟨110⟩NM preferred crystallographic orientation, which facilitated the magnetic alignment along easy magnetization axis. Consequently, the giant ΔSm value up to −24.25 J/(kg K) and effective refrigeration capacity RCeff of 198.77 J/kg were further achieved in the trained Ni54Mn25Ga20.7Dy0.3 alloy under an external magnetic-field change of 5.0 T.

Microstructural and nonlinear optical properties of quaternary gallium-titanium-zinc-oxide transparent conductive semiconductor thin films

Transparent and conductive quaternary gallium-titanium-zinc-oxide films were grown on glass substrates by radio-frequency magnetron sputtering. The effects of growth temperature on structure, morphology, electrical, and nonlinear optical properties of the films were investigated systematically. All the deposited films possess hexagonal wurtzite structure with (002) preferred crystallographic orientation. The obtained optical bandgaps of the deposited films are larger than that of pure zinc oxide, which is ascribed to the reduction in band tail width. The film deposited at growth temperature of [Formula: see text]C exhibits the optimum crystalline quality with the lowest dislocation density of [Formula: see text] nm[Formula: see text], the highest visible light transparency of 82.06%, the minimum sheet resistance of 11.2 [Formula: see text]/sq, and the maximum figure-of-merit of [Formula: see text] [Formula: see text][Formula: see text]. The present findings indicate that the gallium-titanium-zinc-oxide films are promisingly utilized as transparent conductive layer. The refractive index and extinction coefficient of the deposited films were estimated by using spectrum fitting approach. A normal optical dispersion behavior was observed in visible region, while an anomalous dispersion behavior appeared in ultraviolet region. In addition, the nonlinear optical parameters were obtained. This first-hand information is useful for future rational design of multicomponent zinc oxide semiconductor materials for optoelectronic applications.

Attachment of facile synthesized NaCo2O4 nanodots to SiO2 nanoflakes for sodium-rich boosted Pt-dominated ambient HCHO oxidation

Surface alkali metal ions are typically utilized as available promoters for ambient HCHO oxidation. In this study, NaCo2O4 nanodots with two different preferential crystallographic orientations are synthesized by facile attachment to SiO2 nanoflakes with varying degrees of lattice defects. A unique Na-rich environment is established through interlayer Na+ diffusion based on the small size effect. The optimized catalyst Pt/HNaCo2O4/T2 can deal with HCHO below 5 ppm in the static measurement system with a sustained release background and produces approximately 40 ppm of CO2 in 2 h. Combining the experimental analyses with density functional theory (DFT) calculations, the possible catalytic enhancing mechanism is proposed from the support promotion perspective, and the positive synergistic effect of Na-rich, oxygen vacancies and optimized facets for Pt-dominant ambient HCHO oxidation via both kinetic and thermodynamic processes is confirmed.