Fine-grained Layer Research Articles

Recovery of aquifer-systems in Southwest US following 2012–2015 drought: Evidence from InSAR, GRACE and groundwater level data

During the drought period 2012–2015, some of the major metropolitans and agricultural hubs within the Southwest US, including Phoenix and Tucson in Arizona, San Joaquin Valley in California, Colorado Springs in Colorado, Las Vegas in Nevada, and Albuquerque in New Mexico, experienced significant groundwater overdraft. At the end of the drought, GRACE-based estimates of total water storage show a rising trend. Also, the precipitation anomalies, considering monthly averages over 2002–2017, are positive. But, it is unclear if a pressure equilibrium is achieved within the aquifer systems, which is a requirement for residual compaction to halt. To this end, we perform a multidisciplinary multi-resolution analysis of space-borne and ground-based observations. We find that following the drought period and during wetter years, due to reduced pumping, owing to significant precipitation and the supply of surface water, groundwater levels begin to rise at all sites while compaction of aquifer-systems continues. A multi-temporal interferometric analysis of Sentinel-1A/B SAR datasets during Nov. 2014–Nov. 2017 shows subsidence rates of ~6 mm/yr, ~3 mm/yr, ~200–300 mm/yr, ~3–4 mm/yr, ~4–6 mm/yr, ~2 mm/yr affecting parts of Phoenix, Tucson, San Joaquin Valley, Colorado Springs, Las Vegas, Albuquerque, respectively, which are attributed to delayed compaction of fine-grain aquitard layer. We conclude that the aquifer-systems did not reach pressure equilibrium at least within ~2.5 years following the drought. The data provided here can assist policymakers and urban planners to improve groundwater management plans in the southwest and elsewhere.

Effect of Na2S soaking on the properties of Cu2ZnSn(S,Se)4 films and solar cells

In this paper, we propose a Na2S soaking process (used as post-treatment process for the precursor films) for the non-vacuum prepared Cu2ZnSn(S,Se)4 (CZTSSe) films. The CZTSSe film prepared without this process show triple-layer structure in which fine-grain layer and obvious layer-boundaries exist. By soaking the precursor film in Na2S aqueous solution with suitable concentration, the fine-grain layer in the triple-layer structure is substituted by a small-grain layer and the layer-boundaries become continuous. We find the quantum efficiencies of the solar cells in long wavelength region are improved by the Na2S soaking. Therefore, the short-circuit currents of the solar cells are significantly increased. By using the Na2S soaking process, CZTSSe solar cells with the best efficiency of 11.5% have been prepared.

Design of a high strength, high ductility 12 wt% Mn medium manganese steel with hierarchical deformation behaviour

A novel medium Mn steel of composition Fe-12Mn-4.8Al-2Si-0.32C-0.3V was manufactured with 1.09 GPa yield strength, 1.26 GPa tensile strength and 54% elongation. The thermomechanical process route was designed to be industrially translatable and consists of hot and then warm rolling followed by a 30 min intercritical anneal. The resulting microstructure comprised of coarse elongated austenite grains in the rolling direction surrounded by necklace layers of fine austenite and ferrite grains. The tensile behaviour was investigated by in-situ neutron diffraction and the evolution of microstructure studied with Electron Backscattered Diffraction (EBSD). It was found that the coarse austenite grains contributed to the first stage of strain hardening by transforming into martensite and the fine austenite necklace grains contributed to the second stage of strain hardening by a mixture of twinning and transformation induced plasticity (TWIP and TRIP) mechanisms. This hierarchical deformation behaviour contributed to the exceptional ductility of this steel.

Anisotropy of microstructure and tensile properties of Ti–48Al–2Cr–2Nb fabricated by electron beam melting

The anisotropy of Ti–48Al–2Cr–2Nb (TiAl-4822) fabricated by electron beam melting (EBM) with 3 different microstructures, namely hot isostatic pressing (HIP), duplex (DP) and fully lamellar (FL) microstructure was investigated. Results show that the HIP material exhibits microstructure with alternating layers of coarse and fine grains. The α2 phase is more concentrated in the layer of fine grains and exhibits a strong texture with (0001) nearly perpendicular to the building direction, which further leads to the preferential orientation of lamellae. Non-uniform distribution of Al results in the selective formation of lamellar colonies in DP microstructure. The variation of critical resolved shear stress (CRSS) for slip activation is believed to cause the anomalous temperature dependence of yield strength at intermediate temperature. For all 3 microstructures, the ductility in Z direction is lower compared with XY direction, which is attributed to the difference in crack initiation mode and preferential orientation of lamellae.

Microstructural changes caused by friction loading in high manganese TWIP steel and case-hardened 16MnCr5

In this study, the morphological, structural and chemical changes during friction loading of a metastable fully austenitic TWIP steel and of a case-hardened carburized 16MnCr5 steel were investigated by various methods. To do so, EFTEM imaging, SAD, TEM-XEDS, TEM-EELS, XRD, EBSD, and ACOM-TEM were applied for the unloaded state and after defined friction loading. Although the investigated materials appeared very different in their unloaded states concerning their phase compositions, grain sizes and mechanical properties, the friction loading led to significant, but comparable changes in both materials. These changes start immediately from the worn surface and continue towards the sample depth. An extremely fine-grained nanocrystalline surface layer with a thickness of several hundred nanometers and a nanocrystalline sub-surface layer were formed with sharp interfaces between them. The grain size remains nearly constant within the first layer, but increased immediately crossing the interface between these layers and gradually enlarges further within the sub-surface layer with increasing distance to the interface. These layers differ tremendously from the unloaded states and were characterized in a detailed way. Explanations for the formation of these layers were supposed.

Influence of the selenization condition on the properties of ambient-air processed CZTSSe thin films and device performance

Thoroughly understanding and well controlling the structure and grain growth of Cu2ZnSn(S,Se)4 (CZTSSe) absorber layer in CZTSSe solar cells are essential for getting high power conversion efficiency. Herein, the Cu2ZnSnS4 (CZTS) precursor films were prepared in ambient-air condition by solution method and the effects of selenization condition on the microstructure and device performance are systematically investigated. It is found the heating-up time determines the formation manner of both top large-grained and middle fine-grained layer, while the substrate affects the growth of bottom large-grained layer. A proper heating-up time could effectively optimize the fine-grained layer and achieve better crystallined CZTSSe absorber layer together with a higher device efficiency of 3.38%. A growth mechanism is suggested for the structure formation of CZTSSe.

Improved Mechanical Properties, Wear and Corrosion Resistance of 316L Steel by Homogeneous Chromium Nitride Layer Synthesis Using Plasma Nitriding

Here, pulsed plasma nitriding of AISI-316L austenite stainless steel is conducted in a narrow range of temperature 510-550 °C and simultaneous combination of expanded austenite phase, and homogenous, dense chromium nitride phase is attained in a single processing unit, with relative low-cost equipment and single-step processing. The results show a noteworthy enhancement in nanohardness at 530 °C, whereas best wear resistance is achieved by processing at 550 °C. A dual-layer structure is obtained constituted of expanded austenite phase covered by quite homogenous chromium nitride phase, which is probably responsible for the dramatic surface improvement. The wear mechanism is changed after plasma processing (abrasive to adhesive wear), and the friction coefficient is reduced and smoother, particularly for the sample treated at 530 °C. Interestingly, the corrosion resistance is also found to be enhanced, even in the presence of chromium nitride (which usually deteriorate the corrosion resistance), which is probably credited to the formation of fine-grained and homogeneous CrN layer over the expanded austenite phase. This study suggests that the development of homogenous CrN layer over the expanded austenite structure is highly valuable for mechanical and tribological features, and it enhances the corrosion resistance.

AoA-Aware Probabilistic Indoor Location Fingerprinting Using Channel State Information

With expeditious development of wireless communications, location fingerprinting (LF) has nurtured considerable indoor location based services (ILBSs) in the field of Internet of Things (IoT). For most pattern-matching based LF solutions, previous works either appeal to the simple received signal strength (RSS), which suffers from dramatic performance degradation due to sophisticated environmental dynamics, or rely on the fine-grained physical layer channel state information (CSI), whose intricate structure leads to an increased computational complexity. Meanwhile, the harsh indoor environment can also breed similar radio signatures among certain predefined reference points (RPs), which may be randomly distributed in the area of interest, thus mightily tampering the location mapping accuracy. To work out these dilemmas, during the offline site survey, we first adopt autoregressive (AR) modeling entropy of CSI amplitude as location fingerprint, which shares the structural simplicity of RSS while reserving the most location-specific statistical channel information. Moreover, an additional angle of arrival (AoA) fingerprint can be accurately retrieved from CSI phase through an enhanced subspace based algorithm, which serves to further eliminate the error-prone RP candidates. In the online phase, by exploiting both CSI amplitude and phase information, a novel bivariate kernel regression scheme is proposed to precisely infer the target's location. Results from extensive indoor experiments validate the superior localization performance of our proposed system over previous approaches.

Age of metamorphism and deformation in the Montagne Noire dome (French Massif Central): Tapping into the memory of fine-grained gneisses using monazite U-Th-Pb geochronology

Recent work has revealed that the Montagne Noire dome, located in the foreland of the Variscan belt (French Massif Central), contains a record of nearly coeval, late Variscan eclogitization and migmatization. Given these new results, it is important to understand the chronology of events that produced high-grade metamorphism and exhumation. Using U-Th-Pb dating of monazite, this study confirms ages of ~315–300 Ma for high-T metamorphism in the augen gneiss that makes up a large fraction of the Montagne Noire dome, and documents for the first time ~295 Ma monazite ages in compositionally varied fine-grained gneisses that form folded continuous layers within the core of the dome. The fine-grained gneiss layers are intensely sheared and are interpreted to have localized late, high-T deformation in the core of the dome. These sheared fine-grained gneisses form a network of shear zones that were kinematically linked to the extensional and strike-slip deformation zones that exhumed the Montagne Noire dome in a pull-apart (s.l.) domain. Continued deformation-recrystallization and fluid flow within these shear zones likely drove rejuvenation of monazite for ~5 million years after much of the melt had crystallized in the Montagne Noire dome.

Microstructural evolution of AZ31 Mg alloy with surface mechanical attrition treatment: Grain and texture gradient

Nanocrystalline surface layers and gradient nanostructures are produced in AZ31 Mg alloy through surface mechanical attrition treatment (SMAT). The grain sizes in the surface layer of the alloy are significantly refined to a nanoscale after SMAT. A gradient nanostructure is formed in which the grain size increases gradually from surface to matrix. The microhardness of the surface layer and the tensile strength of the alloy are significantly improved, but with a certain loss of fracture elongation. SEM photographs of tensile fracture of samples after SMAT show that the fractures of the GNS layer are brittle fractures with poor toughness, while the plasticity of the matrix is better, and the fractures exhibit typical ductile features. To investigate the effect of SMAT on the textural evolution of AZ31 Mg alloy, electron backscatter diffraction is used to analyze the as-received sample and samples after SMAT. The non-basal plane orientation is increased and the basal texture is significantly weakened in the fine-grained layer after SMAT. The weakening of the basal texture reduces the anisotropy of the mechanical properties of Mg alloys, which is beneficial for their industrial application.

Study on Sedimentary Records of Paleoclimate and Paleoenvironmental Evolution of the Dongsha Atoll of South China Sea in Recent 70 Thousand Years

The Dongsha Atoll of South China Sea are located on the western reef terrace of Dongsha Atoll, where a large amount of terrigenous clastic materials and marine biomass are accumulated, which play an important role in the global material cycles. In recent years, the water level in this area has been on the decrease along with the frequent occurrence of floods, red tides, low-oxygen conditions and warmer waters as a result of worsening global ecology. In this paper, accelerated mass spectrometer (AMS) 14C was used to analyse the sediments in Dongsha Atoll of South China Sea, and studied the organic matter deposition in this area in the past 70,000 years combined with sediment grain size, geochemistry and other indicators, which revealed the influence of paleoclimate environment and climate change on the development of this area. The results showed that the environment and climate are essential to the distribution of particles, which can be divided into three layers from bottom to top, i.e., calcium-rich layer, organic matter layer and fine-grained sediment layer. Al2O3, K2O, TFe2O3 and MgO contribute 58.84% to the total variance, indicating that the composition plays a decisive role in the content of major elements in the region. Turbidity sediments have been widely distributed in different areas of the region since last glacial period, among which turbidity occurred most frequently in the period 200,000 years ago when the sea level was relatively low. This study provided a theoretical basis for the evolution of climate and environment in the South China Sea.

High Machinability of Plasma-Nitrided HPM80 Dies at 673K by PCD-Tools for Hot Mold-Stamping

HPM80 had been utilized as one of the martensitic stainless steel mold and die substrates for stamping. In particular, HPM80 mold was often used as hot-stamping molds for oxide glasses and optical polymers to fabricate the optical elements and DOE (Diffractive Optical Elements) with the aid of NiP (Nickel Phosphate) and NiWP (Nickel-Tungsten Phosphate) coatings. These machinable amorphous coatings were indispensable to cut and finish the tailored micro textures for DOE since HPM80 was difficult or nearly impossible to be finished by using the PCD (Poly-Crystal Diamond)-chipped tools. However, those coatings were fragile above 473 K; the original HPM80 must be modified to be fine machinable even by the diamond-chipped and coated tools for fine finishing to mirror-polished die surfaces with far less damage to cutting tools. These HPM80 substrates were plasma nitrided at 673 K under the nitrogen and hydrogen mixed gas flow to form the high content nitrogen super-saturated layer. Precise machinability experiment was performed with the use of the PCD coated WC (Co) tools to investigate the machinability of these nitrogen supersaturated HPM80 substrates. Two-phase fine-grained layer with higher nitrogen solute content than 2 mass% was machined in the ductile mode with adaptively high quality to shaping and finishing the mold die surface for stamping. Through the hardness testing, this nitrogen super-saturated die surface had higher hardness than 1400 HV; it had sufficient durability for long-term stamping operations. Finally, the turning test was employed to demonstrate that this nitrogen supersaturated HPM80 layer with the thickness of 40μm was machined with high quality to form the mirror-polished surface.

Hydrogeological site investigation and economic evaluation to assess the potential of managed aquifer recharge in the Lower Jordan Valley

Improving water availability and distribution is key to combatting water stress in semi-arid regions. This study presents an approach that integrates hydrogeological surveys and economic analysis at a pilot site in the eastern Lower Jordan Valley to assess the potential for managed aquifer recharge (MAR). Based on exploratory drillings, hydraulic tests, water-quality analyses and previous studies, an appropriate storage space in the alluvial fans along the eastern margin of the valley was found. Average measured infiltration rates of 9.8 × 10−5 m/s in a gravel pit and average hydraulic conductivity values of 6.8 × 10−5 m/s in the aquifer indicate that up to 1 Mm3/year can be infiltrated and stored underground. It is assumed that water is trapped towards the center of the valley where the alluvial sediments inter-finger with fine-grained layers. An increase in electrical conductivity values in the same direction probably indicates irrigation return flow and the presence of evaporitic layers and suggests a water recovery before reaching these saline zones. Depending on whether the water provided by MAR is used for irrigation or domestic water purpose, an average incremental profit of 0.81 and 2.44 US$/m3 can be achieved, respectively. These calculations result in a net present value of the MAR plant of 10.6 or 31.9 million US$, respectively, over a lifetime of 30 years. The presented study serves as a basis for further investigations and planning of a MAR plant, and can be transferred and upscaled to other sites in the Jordan Valley.

Influence of Laser Power on Grain Size and Tensile Strength of 5A90 Al–Li Alloy T-joint Fabricated by Dual Laser-Beam Bilateral Synchronous Welding

Dual laser-beam bilateral synchronous welding is introduced to produce the 2.5 mm thick 5A90 Al–Li alloy T-joint. The grain morphology and grain size of weld metal (WM) in the T-joint are analyzed and calculated. The tensile experiment, scanning electron microscopy and energy disperse spectroscopy are respectively employed to study the tensile strength, fracture morphology and chemical composition of the T-joint. The results reveal that when the laser power is increased from 2500 to 3000 W, the grain sizes of fine-grained layers and columnar dendrites near the fusion line are significantly reduced. Conversely, that of equiaxed dendrites at the WM center is not sensitive to the variety of laser power. Moreover, the degree of elemental segregation in WM near the fusion line is also aggravated with the increasing of the laser power. The tensile strength of the T-joint with the laser power of 2500 W is significantly higher than that with the laser power of 3000 W. The tensile fracture locations are occurred in the weld toe with obvious pores, shear dimples and tear ridges, which are the typical characteristics of ductile fracture. Besides, the chemical compositions of the second phase particles in the WM are more sensitive to than the variation of laser power compared with that of the matrix.

Designing of equipment for the synthesis of coatings from nitrides and carbides of intermetallic Ti-Al systems by condensation of plasma flows generated with vacuum arc

The quality characteristics of Ti-TiN multilayer vacuum ion-plasma coatings are studied, among which are as follows: roughness and adhesive strength. It is shown that additional ion bombardment contributes to obtaining high-quality coatings. Ion bombardment has a significant impact on the state of metal surface layer. In the process of ion bombardment, the conditions for formation of active adsorption centers as well as formation of a fine-grained structure, nanoscale grains and layers are created.

On the sound speed dispersion and the frequency dependence of sound attenuation in a fine-grained sediment in the New England Mud Patch

The study on the sound speed dispersion and the frequency dependence of sound attenuation in marine sediments is of great importance in understanding the physics of sound propagation in the sea bottom. Modal dispersion curves (MDC) have only been utilized to estimate the low-frequency sound speed. At higher frequencies (i.e., above a few hundred hertz), arrival time difference for different modes generally become smaller and MDC is difficult to extract because of the cross-mode interference. This paper applies time-frequency representations (TFR) with high time-frequency resolution (e.g., optimal-kernel and center-affine-filtered TFR) to broadband acoustic signals (e.g., 31g explosive and combustive source signals) detonated along the 15-km Northwest-Southeast tracks during the Seabed Characterization Experiment in the New England Mud Patch, which has a surface fine-grained sediment layer overlying a sandy bottom. The resulting high-resolution broadband (150–1500 Hz) MDC, in conjunction with TL data, are fed to a previously developed two-step dimension-reduced geoacoustic inversion algorithm including modal dispersion-based inversion for sound speed and energy-based inversion for attenuation [IEEE J. Ocean. Eng., 44, in print, (2019)]. The estimated sound speed and attenuation are compared with the theoretical results from seabed geoacoustic models for fine-grained sediments. [Work supported by ONR Ocean Acoustics (322OA).]The study on the sound speed dispersion and the frequency dependence of sound attenuation in marine sediments is of great importance in understanding the physics of sound propagation in the sea bottom. Modal dispersion curves (MDC) have only been utilized to estimate the low-frequency sound speed. At higher frequencies (i.e., above a few hundred hertz), arrival time difference for different modes generally become smaller and MDC is difficult to extract because of the cross-mode interference. This paper applies time-frequency representations (TFR) with high time-frequency resolution (e.g., optimal-kernel and center-affine-filtered TFR) to broadband acoustic signals (e.g., 31g explosive and combustive source signals) detonated along the 15-km Northwest-Southeast tracks during the Seabed Characterization Experiment in the New England Mud Patch, which has a surface fine-grained sediment layer overlying a sandy bottom. The resulting high-resolution broadband (150–1500 Hz) MDC, in conjunction with TL data, are ...

Effect of the surface nanocrystallization on tribological behavior of the Cu based bimetallic materials (CuPbSn)

In this study, ultrasonic impact treatment was used to improve the tribological behavior of copper-based bimetallic materials that are used in internal combustion engine bearings and bushes. Bimetallic materials were obtained by coating three different CuPbSn alloys by sintering on the material surfaces of carbon steel substrate. After the sintering process, bimetallic materials were treated by ultrasonic impact process. As a result of the metallographic examination, sintered layers have uniform structure along the cross-section of the bimetallic materials. In addition, it was determined that the porosity of sintered materials decreased after the ultrasonic impact treatment. Due to the grain refinement and work hardening, higher hardness was obtained in the fine-grained layer. The hardness of the ultrasonic impact treated samples always higher than the untreated material. Because of the high surface hardness, ultrasonic impact treated samples showed higher wear resistance. The highest wear resistance was detected in the samples with the highest Sn content. Because Sn and Cu combine to form Cu3Sn intermetallic phase in Cu-Pb alloys and Cu3Sn increases the strength of the Cu-Pb alloys. Thus, increasing the Sn content in the Cu-Pb alloy resulted in the wear resistance increase. Furthermore, the formation of the SnO2 intermetallic phase on the sample surface has a significant effect on the wear resistance increase by preventing adhesion.

CuZnSn(SxSe1-x)4 Solar Cell Prepared by the Sol-Gel Method Following a Modified Three-Step Selenization Process

In current work, Cu2ZnSn(S,Se)4 thin films have been prepared by the sol-gel method based on dimethyl sulfoxide solution followed by a modified three-step selenization process. The key process of this method is to divide the Se evaporation and annealing into two different stages: employ a thermal cracking Se source in the Se evaporation stage and an above-atmospheric pressure in the annealing process. The morphological, structural, elemental distributional, and photovoltaic properties of Cu2ZnSn(S,Se)4 thin films prepared with the three-step selenization process were systematically investigated. It was found that through this modified selenization process, the formations of secondary phases (ZnSe, CuSnSe3) and a fine-grain bottom layer, which usually exists in the traditional one-step selenization process, were effectively suppressed. These improvements could further reduce the carrier recombination and improve the solar cell performance. The best solar cell is obtained with a short-circuit current density of 28.16 mA/cm2, open-circuit voltage of 404.91 mV, fill factor of 62.91%, and a power conversion efficiency of 7.17% under air mass 1.5 (100 mW/cm2) illumination.

Mechanical behaviour of AZ31 magnesium alloy with the laminate and gradient structure

ABSTRACTA laminate and gradient structured (LGS) AZ31 magnesium alloy was produced via a combination of surface mechanical attrition treatment (SMAT) and accumulative roll-bonding (ARB) in an attempt to improve the AZ31 strength-ductility relationship. The effects of the rolling temperature and number of passes on the microstructure and mechanical properties were researched. The LGS AZ31 Mg alloy microstructure included periodic distributions of fine grain (FG) layers, coarse grain (CG) layers, and FG layers in which the grain size exhibited a gradient transition. A depth-dependent gradient microhardness was generated because of the corresponding gradient microstructure. The effect of the LGS AZ31 Mg alloy on grain size-dependent strengthening mechanisms was researched. The yield and ultimate tensile strengths of the alloy improved dramatically and there was a slight decrease in the fracture elongation. The tensile properties of the sample present good strength-ductility relationships. This is attributed to LGS. The microstructure could change the crack propagation path and enhance alloy strength without much harm to plasticity. The overall influences of SMAT and ARB on mechanical properties, which include dynamic recrystallisation, dislocation activity, and the influences of interfaces, were researched. To illuminate the differences in the deformation behaviours of FG and CG layer microstructures, tensile test samples were imaged via SEM.

Maximum Entropy Derived Statistics of Sound-Speed Structure in a Fine-Grained Sediment Inferred From Sparse Broadband Acoustic Measurements on the New England Continental Shelf

Marginal probability distributions for parameters representing an effective sound-speed structure of a fine-grained sediment are inferred from a data ensemble maximum entropy method that utilizes a sparse spatially distributed set of received pressure time series resulting from multiple explosive sources in a shallow-water ocean environment possessing significant spatial variability of the seabed. A remote sensing seabed acoustics experiment undertaken in March 2017 off the New England Shelf was designed so that multiple independent analyses could infer the statistical properties of the seabed. The current analysis incorporates the measured horizontal variability from interpretations of a subbottom profiling survey of the experimental area. An idealized range- and azimuth-dependent parameterization of the seabed is derived from identification of horizons within the seabed that define multiple sediment layers. A sparse set of explosive charges were deployed on circular tracks with radii of about 2, 4, and 6.5 km with an acoustic array at the center to correlate a set of random measurements to physical acoustic processes that characterize the seabed. The mean values of a surface sound speed ratio and a linear sound speed gradient for the fine-grained sediment layer derived from 12 data samples processed in the 25-275-Hz band provide an estimate of the effective sound-speed structure in a 130-km <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> area. The inferred sediment sound speed values are evaluated by predicting measured time series data not used in the statistical inference, and are also compared to historical measurements. Finally, the low-frequency maximum entropy estimate of the sediment sound speed along with physical measurements derived from piston core measurements are utilized to estimate the sediment grain bulk modulus.