Grain Size Measurements Research Articles

Metallic material microstructure grain size measurements from backscattering signals in ultrasonic array data sets

Ultrasound backscattering signals from material microstructures can be used to evaluate the material microstructure grain size. This typically involves making pulse-echo immersion measurements at multiple locations using a focused ultrasonic transducer in order to obtain an accurate estimate of the root-mean-square amplitude of the back-scattered signal at a specified focal position. However, this restricts some practical applications of using such techniques in, for example, on-line measurements in high-value manufacturing and in-service inspections where multiple immersion measurements are not feasible to use. The main benefit of using ultrasonic phased arrays is that one array probe at one position can focus ultrasound beams at multiple points using different focal laws either physically or in data postprocessing. Potentially this means that accurate grain size measurements can be obtained from a single array measurement. In this paper, the classic backscattering method for conventional transducers is adapted to be used for full matrix capture datasets from an ultrasonic array. Three-dimensional ultrasonic models are developed in the proposed inverse process to measure material microstructure grain size. Experimental validations were performed on two metallic materials: copper (EN1652) and bright mild steel (BS970). A good agreement is shown between the experimentally measured grain sizes from array data and metallography measurements. Compared to the classic pulse-echo immersion back-scattering measurements, the proposed method enables accurate measurement of grain size in a direct contact configuration at fewer locations. This has potential to make on-line grain size measurements possible.

Variable preservation of the 1991 Hudson tephra in small lakes and on land

Volcanic ash (tephra) preserved in terrestrial environments and lake sediments contains information about volcanic processes and can be used to infer eruptive parameters and frequency of past eruptions, contributing to the understanding of volcanic hazards. However, tephra deposits can undergo transformation from their initial fallout sedimentation to being preserved as a tephra layer in the sedimentary record. The process is likely to be different in lakes and in terrestrial (soil) sequences. Here we compare the thickness, mass loading and grain size of tephra layers from the 1991 eruption of Cerro Hudson, Chile, from small lakes and adjacent terrestrial settings to measurements of the tephra made shortly after the eruption. We analysed samples from 35 cores in total from six small lakes (<0.25 km2), located 76 and 109 km from the volcano in two contrasting climatic areas (cool and humid northern site, and warm and dry southern site), and made 73 measurements of tephra thickness and 11 measurements of grain size in adjacent terrestrial areas. The major element geochemistry of our samples confirmed they were from the 1991 Hudson eruption. We found that some of the measured characteristics of the preserved tephra layers were comparable to those recorded in 1991 shortly after initial deposition, but that there was considerable variability within and between locations. This variability was not predictable and lake sediments did not preserve a notably more accurate record of the fallout than terrestrial sites. However, in aggregate the characteristics of the preserved tephra was similar to those recorded at the time of deposition, suggesting that, for palaeotephra research, a sampling strategy involving a wide range of environments is more robust than one that relies on a single sedimentary record or a single type of sedimentary environment.

Grain-size measurements in protoplanetary disks indicate fragile pebbles and low turbulence

Context. Constraining the turbulence level and pebble size in protoplanetary disks is an essential initial step in understanding the aerodynamic properties of pebbles, which are crucial for planet formation. Recent laboratory experiments have revealed that destructive collisions of icy dust particles may occur at much lower velocities than previously believed. These low fragmentation velocities push down the maximum grain size in collisional growth models. Aims. Motivated by the smooth radial distribution of pebble sizes inferred from ALMA/VLA multi-wavelength continuum analysis, we propose a concise model to explain this feature and aim to constrain the turbulence level at the midplane of protoplanetary disks. Methods. Our approach is built on the assumption that the fragmentation threshold is the primary barrier limiting pebble growth within pressure maxima. Consequently, the grain size at the ring location can provide direct insights into the turbulent velocity governing pebble collisions and, by extension, the turbulence level at the disk midplane. We validate this method using the Dustpy code, which simulates dust transport and coagulation. Results. We applied our method to seven disks, namely TW Hya, IM Lup, GM Aur, AS 209, HL Tau, HD 163296, and MWC 480, for which grain sizes have been measured from multi-wavelength continuum analysis. A common feature emerges from our analysis, with an overall low turbulence coefficient of α ~ 10−4 observed in five out of seven disks when assuming a fragmentation velocity υfrag = 1 m s−1. A higher fragmentation velocity would imply a significantly larger turbulence coefficient than that suggested by current observational constraints. IM Lup stands out, with a relatively high coefficient of 10−3. Notably, HL Tau exhibits an increasing trend in α with distance. This supports enhanced turbulence at its outer disk region, which is possibly associated with the infalling streamer onto this particular disk. Alternatively, if the turbulence were found to be low, this might indicate that grain sizes have not reached the growth barrier. Conclusions. We conclude that the current (sub)mm pebble size constrained in disks implies low levels of turbulence; it also implies fragile pebbles, which is consistent with recent laboratory measurements.

Automated grain sizing from uncrewed aerial vehicles imagery of a gravel‐bed river: Benchmarking of three object‐based methods

AbstractMeasuring grain sizes in gravel‐bed rivers is crucial when studying river dynamics and sediment transport. Automated methodologies have been developed in recent years for detecting individual grains and measuring their size on digital imagery. These object‐based methodologies have mainly been applied to handheld imagery. Low‐cost and high‐resolution orthoimages covering long river reaches are nowadays accessible with the improvements in uncrewed aerial vehicles (UAV) and structure‐from‐motion (SfM) photogrammetry. Applying object‐based grain‐sizing methodologies to such orthoimages may provide wide‐scale information about the grain size spatial distribution along streambeds. We examined how accurate three object‐based models (BASEGRAIN, PebbleCountsAuto and GALET) were, by comparing their outcomes to in‐field manual measurements of grain sizes and manual grain labelling. We found that BASEGRAIN and PebbleCountsAuto underestimated grain sizes on average, whereas GALET generally overestimated grain size percentiles. Grain size measurements obtained by manually labelling grain features were consistent with in‐field measurements.

Assessment of two grainsize methods for peat sediments and their paleoenvironmental significance: the Yueliangwan Peatland in northeast Asia

Grainsize is an important indicator in paleoenvironmental research. Over the past few decades, different pretreatment methods have been proposed for grainsize determination of peat sediments. Assessing the reliability of the grainsize measurements is critical to ensure the paleoenvironmental significance represented by different grainsize components. In this study, using peat sediments from the Yueliangwan peatland in northeast Asia, the effects of two pretreatment methods on grainsize measurement were compared. It was found that these two pretreatment methods on peat sediments produced grainsize features with totally different parameters and distribution characteristics. Grainsize method 1, which used a hydrogen peroxide water bath treatment, did not reflect accurate results for grainsize in peat sediments. Grainsize method 2, which used muffle furnace combustion, does reflect the true results because the organic matter, such as plant residues, spores and pollen, is totally removed. The presence of this stubborn organic matter in peat samples greatly disturbs the accuracy of grainsize measurements, and the reliability of grainsize measurements can be affected by the presence of stubborn organic matter. Based on the grainsize grade-standard deviation analysis using method 2, the East Asian Winter Monsoon evolutionary history in northeast Asia during the Little Ice Age (1300–1750 CE) was reconstructed and divided into three stages: the strengthening stage (1346–1425 CE), the strongest stage (1425–1525 CE) and the weakening stage (1525–1725 CE).

High-precision algorithm for grain segmentation of thin sections by multi-angle optical-microscopic images

ABSTRACT This paper introduces an algorithm for automating the analysis of petrographic thin-section images of sandstones and siltstones. The images of thin sections are obtained in polarized light at magnifications providing good image quality. In addition, the images for each section are obtained at different angles of rotation of the microscope stage. Augmentation is applied to the obtained photographs: the number of images increases due to rotations, shifts, and rescaling of the image. For training the neural network of the Mask R-CNN architecture, transfer learning is used, with initial weights obtained from a huge variety of nongeological images. The results of image segmentation using Mask R-CNN are compared to the Watershed algorithm results and the U-Net network for two metrics. According to the standard Intersection over Union metric, U-Net for high-quality images and Watershed for blurry images show the best results with a slight superiority. However, according to the Grain Size Metric, which evaluates the accuracy of grain-size measurement, the best accuracy (over 95%) is shown by Mask R-CNN. The grain-size analysis is done, and the porosity of the studied petrographic sections is determined. The use of the proposed approaches in the study of thin sections will significantly reduce the time for obtaining the results of grain-size-distribution analysis and porosity determination. This article is the result of multidisciplinary collaboration between geologists and programmers. This has allowed for the merging of profound knowledge in the field of geology with cutting-edge data processing technologies. By employing the presented methodology, geologists can devote more time to interpreting results rather than obtaining them, which in turn enhances the efficiency of research work. The benefits of using this methodology are not limited to just speeding up the process: it also allows for increased accuracy and reliability of the analysis, minimizing human error.

Leachate Lithium Characteristics of Loess‐paleosol Sequences on the Chinese Loess Plateau and their Paleoclimatic Significance

AbstractThe geochemical components of the leachate from loess‐paleosol deposits can provide information about climate‐related post‐depositional processes. For example, leachate lithium ([Li]leachate) is a potential paleoclimate proxy because lithium is a typical lithophile element that is readily adsorbed by clay minerals during weathering and pedogenesis, and thus stratigraphic variations in [Li]leachate can reflect these processes. We investigated the [Li]leachate values of two loess‐paleosols profiles (the Luochuan and Weinan sections), on a north–south climatic gradient on the Chinese Loess Plateau. Independent paleoclimate information was provided by measurements of magnetic susceptibility, grain size, Rb/Sr ratios, and clay mineral content. During the last glacial‐interglacial period, [Li]leachate increased from 0.39 to 1.97 μg/g at Luochuan and from 0.67 to 2.45 μg/g at Weinan, mainly due to increasing pedogenesis. Based on these results we developed a conceptual model to explain the variations in [Li]leachate. Li+ within loess layers is mainly derived from dust input and the decomposition of primary minerals, influenced by the East Asian winter monsoon, while in paleosol layers Li+ is mainly derived from clay mineral adsorption during pedogenic processes, influenced by the East Asian summer monsoon.

Non-contact measurements of residual stress distribution and grain size in titanium alloys with laser ultrasonic system

In this study, a laser ultrasonic method is proposed for nondestructive non-contact measurement of both the residual stress depth profile and grain size in Ti-6Al-4 V alloy processed by warm shot peening (WSP). The method utilizes a pulsed laser to generate a surface acoustic wave (SAW) along the cross-section of the sample, and a laser interferometer to detect SAW signals. Laser ultrasonic measurements were performed on the samples treated by WSP at different temperatures (32, 100, 200 and 300 °C). A theoretical model for calculating the residual stress profile and a model to correlate the center frequency shift and the mean grain size of the sample were presented. The results obtained by the laser ultrasonic method were compared with those obtained by X-ray stress measurement, center-hole drilling (CHD), and electron backscattering diffraction (EBSD). The proposed method can measure and locate the maximum compressive residual stress (CRS) in a peened surface layer with a high spatial resolution of approximately 30 µm, allowing for precise extraction of the residual stress profile. This method can also provide an estimation of the grain size through the same experiment. The developed method is promising for the quick and nondestructive measurement of the residual stress profiles and grain size of surface treated metallic materials.

A novel express method for determining WC grain sizes and its use for updating dependencies of coercivity and hardness on WC mean grain size in hardmetals

A new express method for measurements of WC grain sizes in WC-Co hardmetals was developed. This method is as precise as the EBSD grain size measurement method but much faster and thereby less expensive. The new measurement method is based on a peculiar procedure of hardmetal samples' preparation, recording microstructure images and their segmentation followed by determining WC mean grain sizes by use of a specially developed software; the measurement error is less than ±3%. Dependencies of coercivity and hardness on the WC mean grain size of WC-10 wt% Co hardmetal samples were established by the new express measurement method. With the aid of this method the dependencies reported in literature were updated as a result of more precisely determined values of the WC mean grain size compared to those established in literature by conventional methods based on SEM measurements.

Development of a Middle–Late Holocene subaqueous clinoform in the northern Jiangsu coastal zone, western South Yellow Sea

The northern Jiangsu coastal zone (NJCZ) is part of the western coast of the South Yellow Sea and is located between the mouths of the Yellow and Yangtze rivers. The two rivers and the Huaihe River have discharged into the NJCZ at various times during the Holocene. As a result, multi-stage deltas and clinoforms have developed in the NJCZ, including the old Yellow River delta (OYRD) (1128–1855 CE). An old clinoform has recently been identified just below the OYRD, but its age and origin are uncertain because of limited data. In this study, integrated analyses of a new borehole core SYS-1601 penetrating the clinoform were conducted to document the evolution of the NJCZ and to provide a study case for other coastal regions influenced by major river systems and complex hydrodynamic conditions. Analyses included accelerator mass spectrometry (AMS) 14C and optically stimulated luminescence (OSL) dating, measurements of grain size and Sr-Nd isotopes, and identification of benthic foraminifera and ostracoda. Results show that the evolution of the subaqueous clinoform prior to the development of the OYRD in the western South Yellow Sea was concurrent with and genetically linked to the formation of the Huaihe delta on the NJCZ. The clinoform started to form at the same time as the Middle Holocene maximum flooding of the NJCZ at ∼7.0 ka. Cross-shelf progradation of the clinoform was coeval with progradation of the Huaihe delta and terminated at 1128 CE, when the Yellow River changed course and started to discharge off the Jiangsu coast to form the OYRD. The clinoform exhibits an overall coarsening-upward succession, comprising clayey silt and silt in the lower part grading upwards into silt and sandy silt, and its sediment was sourced largely from the Huaihe and Yangtze rivers. During the development of the clinoform from ∼7.0 ka to 1128 CE, the Yellow River did not flow into the South Yellow Sea through the Jiangsu coast for a sufficiently long time to contribute a substantial amount of sediment to the formation of the clinoform. The initiation and evolution of the clinoform were controlled mainly by complex interactions of dynamic processes, geomorphological conditions, and sediment supply into the western South Yellow Sea during the Middle–Late Holocene.

One Relation for All Wavelengths: The Far-ultraviolet to Mid-infrared Milky Way Spectroscopic R(V)-dependent Dust Extinction Relationship

Dust extinction is one of the fundamental measurements of dust grain sizes, compositions, and shapes. Most of the wavelength-dependent variations seen in Milky Way extinction are strongly correlated with the single parameter R(V) = A(V)/E(B − V). Existing R(V)-dependent extinction relationships use a mixture of spectroscopic and photometry observations, and hence do not fully capture all the important dust features or continuum variations. Using four existing samples of spectroscopically measured dust extinction curves, we consistently measure the R(V)-dependent extinction relationship spectroscopically from the far-ultraviolet (FUV) to mid-infrared for the first time. Linear fits of A(λ)/A(V) dependent on R(V) are done using a method that fully accounts for their significant and correlated uncertainties. These linear parameters are fit with analytic wavelength-dependent functions to determine the smooth R(V) (2.3–5.6) and wavelength (912 Å–32 μm) dependent extinction relationship. This relationship shows that the FUV rise, 2175 Å bump, and the three broad optical features are dependent on R(V), but the 10 and 20 μm features are not. Existing literature relationships show significant deviations compared to this relationship especially in the FUV and infrared (IR). Extinction curves that clearly deviate from this relationship illustrate that this relationship only describes the average behavior versus R(V). We find tentative evidence that the relationship may not be linear with R(V)−1 especially in the ultraviolet (UV). For the first time, this relationship provides measurements of dust extinction that spectroscopically resolve the continuum and features in the UV, optical, and IR as a function of R(V), enabling detailed studies of dust grain properties and full spectroscopic accounting for the effects of dust extinction on astrophysical objects.

Massive Protostellar Disks as a Hot Laboratory of Silicate Grain Evolution

Typical accretion disks around massive protostars are hot enough for water ice to sublimate. We here propose to utilize the massive protostellar disks for investigating the collisional evolution of silicate grains with no ice mantle, which is an essential process for the formation of rocky planetesimals in protoplanetary disks around lower-mass stars. We, for the first time, develop a model of massive protostellar disks that includes the coagulation, fragmentation, and radial drift of dust. We show that the maximum grain size in the disks is limited by collisional fragmentation rather than by radial drift. We derive analytic formulae that produce the radial distribution of the maximum grain size and dust surface density in the steady state. Applying the analytic formulae to the massive protostellar disk of GGD27-MM1, where the grain size is constrained from a millimeter polarimetric observation, we infer that the silicate grains in this disk fragment at collision velocities above ≈10 m s−1. The inferred fragmentation threshold velocity is lower than the maximum grain collision velocity in typical protoplanetary disks around low-mass stars, implying that coagulation alone may not lead to the formation of rocky planetesimals in those disks. With future measurements of grain sizes in massive protostellar disks, our model will provide more robust constraints on the sticking property of silicate grains.

Estimating microstructural feature distributions from image data using a bayesian framework.

Many microstructural characterizations methods collect data on a regular pixelized grid. This method of discretization introduces a form of measurement error which can be shown to be proportional to the resolution at which it is collected. Intuitively, measurements made from low resolution data are associated with higher error, but quantification of this error is typically not performed. This is reflected in international standards for measurements of grain size, which only provide a recommended minimum number of sample points per microstructural component to ensure each component is sufficiently resolved. In this work a new method for quantifying the relative uncertainty of such pixelized measurements is presented. Using a Bayesian framework and simulated data collection on features collected from a Voronoi tessellation, the distribution of true geometric properties given a particular set of measurements is computed. This conditional feature distribution provides a quantitative estimate for the relative uncertainty associated with measurements made at difference resolutions. The approach is applied to measurements of size, aspect ratio, and perimeter of given microstructural components. Size distributions are shown to be the least sensitive to sampling resolution, and evidence is presented which shows that the international standards provide an overly conservative minimum resolution for grain size measurement in microstructures represented by a Voronoi tessellation. Layout Description For many materials, their structure when viewed under a microscope can tell researchers a lot about how a material will perform and under what conditions it might fail. However, in order to collect and store this information for study, special high resolution images need to be taken. For imaging at really small scales this imaging process involves scientific equipment that is both expensive and time consuming to use. The resolution, or the amount of physical area on the surface of the material each pixel represents, determines what sort of information can be collected from the image. But these images have measurement error; small differences between what is shown in the image and the material itself. This works examines the relationship between the amount of error in the image and the resolution at which is was collected. A mathematical formula is developed which tells researchers what the range of probable true size are for an object they measured. This gives researchers a better picture at what they are actually looking at. Using a computer simulations, this formula is used to study the process of collecting and analysis material data. The results help show what at resolutions images should be collected to provide accurate the meaningful results for a wide range ofmeasurments. This article is protected by copyright. All rights reserved.

Significance of Annealing Twins in Laser Ultrasonic Measurements of Grain Size in High-Strength Low-Alloy Steels

In this study, we demonstrate the significance of austenite annealing twin boundaries when calibrating laser ultrasonic measurements for gauging austenite grain size in situ during the thermomechanical processing of high-strength low-alloy steels. Simple calculations show how differences in twinning density can lead to errors in grain size measurements if twins are disregarded during calibration and the method is used for a broad range of steels. Conversely, when calibration is performed using alloys with a metastable austenite microstructure at room temperature, the same calibration is suitable for a broad range of HSLA steels, provided that annealing twins are taken into account. Since light optical microscopy does not allow the characterization of annealing twins in low-alloy steel, the verification of the laser ultrasonic results was conducted using the novel approach of comparing the twinned grain sizes obtained using the ultrasonic method in low-alloy steels with the austenite grain maps reconstructed from martensite orientation maps measured using electron backscatter diffraction. Finally, we show how differences in twinning density occur even for alloys with a roughly similar stacking fault energy, further highlighting the importance of annealing twins in the calibration of laser ultrasonic measurements for industrial use.

Analyzing Physical-Mechanical and Hydrophysical Properties of Sandy Soils Exposed to Long-Term Hydrocarbon Contamination

This paper aims to investigate the issue of sandy soil contamination by oil hydrocarbons. Laboratory procedures used to study conditionally pure and contaminated sands include grain-size measurements and evaluation of physical-mechanical and hydrophysical properties. The results of the analysis of sand samples using visual and microscopic studies and sieve analysis show that, unlike in conditionally pure sands, in contaminated samples, the surface of mineral particles is covered by hydrocarbon film. The presence of the latter enables micro- and macroaggregates to be formed. Studies of the physical and hydrophysical properties of sands using a technique with pre-weighed glass containers, as well as a filtering device, SPETSGEO pipes, showed that, in comparison with conditionally pure samples, contaminated specimens of sandy soils have lower densities and higher permeabilities and water yields. Testing the mechanical properties of contaminated sands on the GPP-30 direct shear apparatus using the consolidated dried shear strength method revealed an increase in the angle of internal friction with a decrease in specific adhesion compared to conditionally clean sands.

Innovative Methodology for Physical Modelling of Multi-Pass Wire Rod Rolling with the Use of a Variable Strain Scheme.

This paper presents the results of physical modelling of the process of multi-pass rolling of a wire rod with controlled, multi-stage cooling. The main goal of this study was to verify the possibility of using a torsion plastometer, which allows conducting tests on multi-sequence torsion, tensile, compression and in the so-called complex strain state to physically replicate the actual technological process. The advantage of the research methodology proposed in this paper in relation to work published so far, is its ability to replicate the entire deformation cycle while precisely preserving the temperature of the deformed material during individual stages of the reproduced technological process and its ability to quickly and accurately determine selected mechanical properties during a static tensile test. Changes in the most important parameters of the process (strain, strain rate, temperature, and yield stress) were analyzed for each variant. After physical modelling, the material was subjected to metallographic and hardness tests. Then, on the basis of mathematical models and using measurements of the average grain size, chemical composition, and hardness, the yield strength, ultimate tensile strength, and plasticity reserve were determined. The scope of the tests also included determining selected mechanical properties during a static tensile test. The obtained results were verified by comparing to results obtained under industrial conditions. The best variant was a variant consisting of physically replicating the rolling process in a bar rolling mill as multi-sequence non-free torsion; the rolling process in an NTM block (no twist mill) as non-free continuous torsion, with the total strain equal to the actual strain occurring at this stage of the technological process; and the rolling process in an RSM block (reducing and sizing mill) as tension, while maintaining the total strain value in this block. The differences between the most important mechanical parameters determined during a static tensile test of a wire rod under industrial conditions and the material after physical modelling were 1.5% for yield strength, approximately 6.1% for ultimate tensile strength, and approximately 4.1% for the relative reduction of the area in the fracture and plasticity reserve.

Magnetic properties of surface soils in the upper and middle reaches of the Yarlung Zangbo River Basin, southern Tibetan Plateau, and their environmental significance

SUMMARY The relationship between climate and the magnetic properties of surface soils on the Chinese Loess Plateau (CLP) have been widely used to provide the basis for palaeoclimatic reconstruction, based on the underlying loess/palaeosol sequences. To date, however, there are few investigations of variations in the magnetic properties of surface soils on the Tibetan Plateau (TP), especially on the southern TP. Therefore, it remains unclear whether magnetic properties could be used as proxies for palaeoclimatic reconstruction in the region. In this study, environmental magnetic parameters and bulk sediment grain-size measurements were made on a set of surface samples from the Yarlung Zangbo River Basin (YZRB), on the southern TP, and their environmental significance was evaluated. The results reveal spatial differences in the magnetic properties of the surface soils, likely caused by regional climatic factors. The input of primary magnetic minerals is the driver of the magnetic properties of the samples from the western (Gar-Saga) part of the YZRB, where the magnetic variations are controlled by the influence of wind intensity on the local source material. However, the samples from the eastern region (Gongga-Nyingchi) are significantly affected by the topographic and sedimentary conditions, and there is no relationship between the magnetic properties and climate. The samples from the central part of the study area (Saga-Gongga) show obvious signs of a pedogenic influence on magnetic properties and ultrafine superparamagnetic (SP) and single domain (SD) ferrimagnetic minerals dominate the magnetic susceptibility. Combined with the variation of grain size, this implies the influence of wind intensity and pedogenesis contribute to the magnetic enhancement. However, the pedogenic intensity closely related to precipitation and temperature could offer the possibility of using sedimentary magnetic properties for palaeoclimatic reconstruction. Furthermore, the existence of a distinct pedogenic alteration boundary in the Saga area is consistent with the location of the Indian summer monsoon, which may be the dominant control on the pedogenic intensity.

Additive manufacturing of nano-oxide decorated AlSi10Mg composites: A comparative study on Gd2O3 and Er2O3 additions

AlSi10Mg-based nanocomposites were fabricated by laser powder bed fusion (LPBF) additive manufacturing with the addition of 1 wt% Gd 2 O 3 and Er 2 O 3 nanoparticles. The effect of different process parameters and supplementary remelting on the densification of the samples was evaluated. Results showed that remelting the printed layers could improve the densification. According to the microstructural observations, stacking the nanoparticles on uneven surfaces of irregular AlSi10Mg particles beside van der Waals's attractive force between the adjacent particles eventually forms coarsened clusters in printed samples. The XRD patterns disclosed the partial reaction between the nano-oxides and the aluminum matrix and the formation of some interfacial intermetallic layers, which were also validated by SEM characterization. The measurement of grain size and microhardness implied that the addition of Er 2 O 3 played a more effective role in grain refinement and enhanced the hardness more uniformly compared to Gd 2 O 3 . Overall, the acquired average hardness for both nano-oxide reinforced specimens was greater than the reported values for LPBF-fabricated AlSi10Mg-matrix composites in the past. EBSD analyses revealed that due to the pinning effect of the nanoparticles, particle-rich zones demonstrated higher KAM and grain orientation spread (GOS) values which were attributed to the formation of more GNDs at the matrix/particles interfaces. • The effect of laser remelting on the compactness of the samples was evaluated. • The distribution of the nanoparticles in Al matrix was characterized by the SEM. • Refinement impact of nano-oxide powders on microstructure studied by the EBSD. • Correlation of the microstructural changes with hardness distribution surveyed.

Amplified and suppressed regional imprints of global warming events on the southeastern Tibetan Plateau during MIS 3–2

Large amplitude, rapid climate oscillations, the so-called Dansgaard-Oeschger (D-O) events, are characteristic of the last glacial period. However, lithological evidence of D-O warming events is rare, mainly due to their brevity. Although the Tibetan Plateau (TP) is regarded as especially sensitive to climate change owing to its fragile cryosphere and ecological systems, little is known about the variability of the Indian summer monsoon (ISM) over the TP on millennial to centennial timescales. Here, we use a well-dated loess-paleosol sequence (LPS) in the Niyang River valley on the southeastern TP (SE TP), China, to determine the patterns and timing of millennial-to centennial-scale variations in paleomonsoon strength and to identify their causes. This stratigraphic sequence developed between 39.2 and 21.8 cal kyr BP, covering the late marine isotope stage (MIS) 3/2 transition. Ten paleosol units were identified within the sequence, based on field observations, high-resolution measurements of color, grain size and magnetic properties, as well as mineralogical and geochemical evidence. These paleosol units provide unambiguous evidence of D-O-like abrupt warming events and repeated climatic instability, associated with large-amplitude, abrupt changes of the ISM system over the SE TP. The amplitudes, duration, and frequency of these abrupt ISM strengthening events over the SE TP present unique features, including irregular spacing and varying amplitudes. In general, the amplitude of ISM oscillations was larger during MIS 2 than in the late MIS 3 period. Four well-developed paleosol units suggest that ISM intensity at ∼38.7, 28.3, 25.9 and 23.5 cal kyr BP was notably higher compared to the climate of the Holocene, including the present-day. However, two substantial abrupt warming events of global scale are not recorded within the LZ2 LPS. We suggest that this was because of the amplification and suppression of global warming events over the SE TP, caused by the interplay of global and regional climatic dynamics. Warming amplification occurred during intervals with less snow and glacier ice cover, whereas warming suppression was the result of unusually large snow and glacier ice cover on the TP. We suggest that anomalous fluctuations of the India-Burma Trough of the westerlies to the south of the TP during winter may have played a crucial role in determining the snowfall, snow cover, glacier accumulation, and the transition from warming amplification to warming suppression. Therefore, the anomalous ISM oscillations in the SE TP were the result of the coupling of global and local processes.

How did the climate and human activities modulate the sedimentary evolution of the central Yellow Sea Mud, China

• The sedimentary evolution and provenance variation of Central Yellow Sea Mud was the result of sea level rising at the begin of Holocene and the established shelf circulation after 7.0 ka. • Drastic environmental changes in the Yellow River basin after 4.0 ka induced by weakening of East Asian Summer Monsoon and enhanced human activities increased the sediment accumulation in the Central Yellow Sea Mud. • The sedimentation of Central Yellow Sea Mud was controlled by the sediment supply under the regulation of monsoon climate and human activities after 4.0 ka. The Central Yellow Sea Mud (CYSM) archived important signals of regional environment and climate changes during the Holocene. We performed high-resolution analysis of two sediment cores taken from the CYSM, including measurements of radiocarbon chronology and grain size, as well as the mineralogical and geochemical measurements on the sediment samples. The results indicate that the Yellow River were likely a dominant source of the CYSM before 6.8 ka BP, with minimal contributions from the local small rivers in the Shandong Peninsula and Korean Peninsula, as confirmed by the mineralogical and geochemical evidences. After 6.8 ka BP, the fine-grained sediments accumulated in the CYSM presented a mixture of those from both the Yangtze and Yellow River with an individual contribution of 55 ± 8% and 45 ± 6%, respectively, as the sea level reached its highstand and initiated the establishment of modern shelf circulation. The drastic environmental changes in the Yellow River basin after 4.0 ka BP driven by the weakened East Asian Summer Monsoon and enhanced human activities that significantly increased the sediment yield from the Chinese Loess Plateau should be responsible for the abrupt increase in the fine-grained sediment (<2 μm) accumulation in the CYSM. After 1.4 ka BP the decrease in precipitation in the Yellow River basin resulted in the imbalance between sediment yield and river runoff, which perhaps induced lower channel aggradation and frequent avulsions, and consequently decreased the accumulation rate of the Yellow River-derived sediment in the CYSM. During the Holocene, the rising sea level played a primary role in shaping the sedimentation of the CYSM including the retreated coastline and establishment of shelf circulation system, whereas the monsoonal climate and human activities dominated the terrestrial sediment supply and accumulation in the CYSM after 4.0 ka BP.