Spatial Distribution Of Phases Research Articles

Detection of incipient aqueous alteration in carbonaceous chondrites

We discuss if the detection of aqueous alteration depends on the techniques that are used. We apply different methods to estimate the extent of aqueous alteration on four ungrouped carbonaceous chondrites showing limited aqueous alteration and thermal metamorphism: Chwichiya 002, El Médano (EM) 200, Northwest Africa (NWA) 12957 and NWA 11750, classified as C3 or C3.00-ung. The aim is to propose a reliable methodology to identify the most primitive chondrites. Chwichiya 002, NWA 11750 and NWA 12957 display very primitive matrices and could be amongst the most primitive chondrites currently known, similar to the least altered lithologies of the CM chondrites Paris (CM2.9) and Asuka (A) 12085 (CM2.8), A 12236 (CM2.9) and A 12169 (CM3.0). The structure of organic matter and Cr2O3 in ferroan olivines show that the four meteorites have been less heated than the least metamorphosed standard/reference type 3 chondrite, Semarkona (LL3.00), with Chwichiya 002, NWA 12957 and NWA 11750 similar to the CO3.0 s, Acfer 094 (C2-ung) and Paris meteorites. Chwichiya 002 and NWA 12957 show similar alteration phases and degree of alteration, with high abundances of amorphous material with embedded metal and sulfide, resembling Glass with Embedded Metal and Sulfide (GEMS)-like materials, and tochilinite-cronstedtite intergrowths (TCIs) as the major alteration phases. The matrix in NWA 11750 contains aggregates of nanoscale olivine crystals and abundant carbonates, observed as micrometer-sized carbonate veins surrounding chondrules, and as nanoscale carbonates mixed with the fine-grained materials. It also contains abundant grains of metal and a low abundance of phyllosilicates. El Medano 200 shows a high abundance of magnetite (∼10 vol%), nanoscale phyllosilicates, troilite, and organic matter. The variability of the secondary alteration phases in the meteorites suggests different alteration mechanisms, likely depending on both the starting composition of the meteorites and the composition of the fluids of alteration.Scanning and transmission electron microscopy (SEM and TEM) allow the identification of primitive phases and the composition and spatial distribution of the secondary phases. X-ray diffraction (XRD) can detect alteration products, including some amorphous phases, although this is limited by the small coherence domains of small TCIs and other phyllosilicates. Transmission infrared (IR) spectroscopy can detect phyllosilicate and carbonate, but is ineffective for the detection of amorphous phases, metal, or sulfide. Both matrix defocused electron microprobe analyses (EMPA) and thermogravimetric analysis (TGA) allow detection of hydrated minerals, such as phyllosilicates and carbonates, but are strongly influenced by the presence of organic matter and do not reflect the overall alteration state of a meteorite. We conclude that the assessment of the primitivity of a chondrite is highly technique dependent. We propose a combination of XRD and the Cr2O3 in ferroan olivines or Raman spectroscopy for a rapid characterization of the alteration state of a chondrite and the detection of the most primitive meteorites. Finally, the combination of XRD and TEM allows for the detection of all primary and secondary phases and represents an ideal methodology for the characterization and detailed study of primitive chondrites and the different types of incipient aqueous alteration.

Deep learning based liquid level extraction from video observations of gas–liquid flows

The slug flow pattern is one of the most common gas–liquid flow patterns in multiphase transportation pipelines, particularly in the oil and gas industry. This flow pattern can cause severe problems for industrial processes. Hence, a detailed description of the spatial distribution of the different phases in the pipe is needed for automated process control and calibration of predictive models. In this paper, a deep-learning based image processing technique is presented that extracts the gas–liquid interface from video observations of multiphase flows in horizontal pipes. The supervised deep learning model consists of a convolutional neural network, which was trained and tested with video data from slug flow experiments. The consistency of the hand-labelled data and the predictions of the trained model have been evaluated in an inter-observer reliability test. The model was further tested with other data sets, which also included recordings of a different flow pattern. It is shown that the presented method provides accurate and reliable predictions of the gas–liquid interface for slug flow as well as for other separate flow patterns. Moreover, it is demonstrated how flow characteristics can be obtained from the results of the deep-learning based image processing technique.

Reactive ceramic aggregates in mortars from ancient water infrastructure serving Rome and Pompeii

Throughout the ancient Roman empire, crushed ceramics were commonly used as additives for surface mortars that were in continuous or frequent contact with freshwater. Inspired by the long-term durability of these materials and employing multi-scale correlative characterization approaches that combine electron microscopy and Raman microspectroscopy-based techniques, we demonstrate the role of these ceramics as a long-term source of reactive aluminosilicates. By mapping the spatial distribution of both pozzolanic and post-pozzolanic phases, our analyses reveal the presence of a hybrid binder consisting of cementitious hydrates and calcite at the interface between the ceramics and the surrounding matrix and provide evidence of post-pozzolanic densification and the filling of pores and cracks. The analysis of a wide range of ancient Roman structures used for the distribution and storage of freshwater demonstrates the ubiquity of ceramic additives for these applications and points to the opportunity for creating more robust modern analogs of these ancient concrete formulations. • Ancient Roman concretes used ceramic fragments as a source of reactive aluminosilicates • C-A-S-H is formed at the ceramic-cement interface, further strengthening these materials • These results pave the way for developing more durable modern concrete formulations Seymour et al. describe how the ancient Romans used crushed ceramics as additives in their mortars and concretes and provide insights into their underlying millennial-scale durability. Analysis of a wide range of ancient freshwater-related mortars points to the opportunity for creating more robust modern analogs of these ancient concrete formulations.

Numerical computation of the effective thermal conductivity of two-phase composite materials by digital image analysis

We consider the numerical determination of the effective thermal conductivity of 2D, two-phase composite materials, whose microstructural geometries are described by digital images. More specifically, key microstructural data pertaining to the spatial distribution and volume fractions of the constituent phases in the material are extracted, along with the shapes of the interphase boundaries, using computer vision techniques. For inclusions of simple shapes (polygons, circles, ellipses), the extracted interphase boundary data is easily obtained and can be exploited immediately (e.g. polygonal vertices) or can be fitted with smooth curves, using least square error minimization techniques in order to reconstruct parametric representations in the case of circular or elliptical boundaries. For more intricate microstructure geometries characterized by clustered or agglomerated intersecting inclusions, piecewise cubic spline functions are adopted to obtain a least-square fitting of the interphase boundaries. The effective thermal conductivities are then calculated based on a boundary integral formulation defined over the reconstructed inclusion boundaries. They are expressed in terms of power series expansions of a conductivity contrast parameter of the constituent phases in the material. To accelerate the convergence of these expansions, nonlinear transformations (known as Padé Approximants) are used to yield rational approximations of the effective thermal conductivity tensor. Tests conducted on a variety of 2D, two-phase microstructures yielded accurate results over a wide range of microstructure image resolution, regardless of the contrast parameters of the constituent phases, thus, validating the efficacy and robustness of the proposed scheme.

The structural analysis of Kunya‐Urgench chondrite: The nondestructive neutron studies

AbstractWe present the results of neutron methods, specifically neutron diffraction and neutron tomography, in studying the structural organization of a Kunya‐Urgench chondrite fragment. The major phases of the meteorite fragment and variation of the phase content across the studied volume were revealed using neutron diffraction. The 3‐D model of the spatial distribution of metal and silicate phases inside the meteorite volume was obtained using neutron tomography. The distributions of volumes, average sizes, and shape‐related parameters of kamacite and silicate phases were analyzed. Shape preferred orientations of the kamacite particles were observed and the origins of shape fabric of these particles were discussed.

Effect of Cu/Mg-containing intermetallics on the mechanical properties of the as-cast HVDC AlSiMgMnCu alloys by SBFSEM at nano-scale

In this study, AlSiMgMnCu alloys with different Cu and Mg contents were fabricated by high vacuum die casting (HVDC) technique. The phase formation and their microstructure evolution are quantitatively studied by serial block-face scanning electron microscopy (SBFSEM) at nano-scale in three-dimensions. Through analyzing their three-dimensional (3D) microstructure, effects of the spatial distribution, volume fractions and morphology of the intermetallic phases on the alloy’s mechanical properties are comprehensively discussed. It is found that, with higher Cu content and lower Mg content, the nucleation and growth of θ-Al2Cu phase would have advantage over Q-Al5Cu2Mg8Si6 phase. In contrast, decreasing Cu/Mg ratio by increasing Mg content is in favor of the nucleation and growth of the Q-Al5Cu2Mg8Si6 phase. The uniformly distributed fine θ-Al2Cu phase provides the highest contribution to the strengthening of the HVDC AlSiMgMnCu alloys. For the Cu/Mg ratio to be 3, an as-cast HVDC Al-10Si-0.2Mg-0.5Mn-0.6Cu alloy with optimized ultimate tensile strength, yield strength and elongation of 330 MPa, 162 MPa and 10.2%, respectively, had been produced.

Mapping mineralogical heterogeneities at the nm-scale by scanning electron microscopy in modern Sardinian stromatolites: Deciphering the origin of their laminations

Stromatolites are found throughout the geological record and have received strong attention because they provide precious information about paleoenvironments and microbial paleobiodiversity. However, while this information is interpreted based on our knowledge about modern analogs, the latter remains incomplete. Here, we investigated the environmental and biological information recorded by modern stromatolites in Mari Ermi, a coastal pond in Western Sardinia that experiences severe seasonal evaporation and large salinity variations. For this purpose, we combined a variety of analytical tools, allowing to characterize the mineralogical composition of these stromatolites from the bulk, centimeter-scale to the nanometer-scale and assess the spatial distribution of the mineral phases. In particular, we used quantified x-ray elemental maps provided by energy dispersive x-ray spectrometry analyses coupled with scanning electron microscopy (SEM-EDXS). These maps were processed using an innovative data treatment allowing (i) mineral phase recognition, (ii) assessment of the mineral formula of each phase and (iii) mapping of their spatial distribution with a spatial resolution down to a hundred nanometers. Overall, this proved as an efficient approach to unravel mineralogical heterogeneities and detect informative mineral phases overlooked by bulk analyses. Mari Ermi stromatolites were mostly composed of magnesian calcite with an average Mg/Ca of ~0.1–0.2 as indicated by bulk analyses. However, microscopy observations revealed variable Mg-contents of calcite with a specific distribution, the most Mg-enriched calcites (Mg/Ca up to ~0.5) being systematically distributed around microbial remnants. Moreover, Mari Ermi stromatolites comprised an alternation of Mg-richer and Mg-poorer laminae, which paralleled the varying enrichment in microbial remnants of alternating laminae. The combination of SEM-EDXS, focused ion beam milling and transmission electron microscopy allowed to detect several minor phases, hardly or not detected at all by bulk analyses, such as aragonite, a variety of clay minerals as well as a gypsum-like phase. An additional calcium sulfate phase, best interpreted as S-apatite (cesanite), was detected by SEM-EDXS. Overall, this mineral assemblage and its definite spatial distribution record only discrete stages of the evaporation of Mari Ermi lagoon. Moreover, microorganisms seem to have a major control on Mg substitution in calcite. As a result, the dynamics of microbial populations, influenced by the salinity variations induced by evaporation in the lagoons, generates the formation of laminae in Mari Ermi stromatolites.

Development of functionally graded ZrB2–B4C composites for lightweight ultrahigh-temperature aerospace applications

In the present work, a lightweight three-layer ZrB2–B4C functionally graded composite material has been developed by spark plasma sintering route. The functionally graded material (FGM) is free from interlayer defects and displays a smooth transition between the individual layers. The composition of each layer was designed to reduce the overall density without sacrificing the functionality of the material. The density of the FGM is almost 40% lower than monolithic ZrB2 and 24% lower than ZrB2–30B4C rendering it potentially very attractive for high-temperature aerospace applications. A detailed structural characterization of the FGM was carried out to evaluate the elemental distribution in the graded composite, as well as determine the spatial distribution of the crystalline phases. Vickers hardness was measured within each layer and in the interlayer regions to further evaluate the gradient structure and interlayer transitions. Longitudinal elastic constants of the FGM along the thickness and across the layers measured using ultrasound phase spectroscopy showed that despite the gradient structure, the FGM can be treated as a quasi-isotropic solid.

Flow Regime Identification in Gas-Liquid Two-Phase Flow in Horizontal Pipe by Deep Learning

Two phase flow commonly occurs in industrial pipelines, heat exchangers and nuclear power plants. A characteristic feature of two-phase flow is that it can acquire various spatial distribution of phases to form different flow patterns/regimes. The first step to successfully design, analyze, and operate gas-liquid system is flow regime identification. Flow regime identification is of huge importance to the effective operation of facilities for the handling and transportation of multiphase fluids, and it represents one of the most significant challenges in petrochemical and thermonuclear industries today. The objective of this study is to develop a methodology for identification of flow regime using dynamic pressure signals and deep learning techniques. Three different flow regimes were simulated using a Level-Set (LS) method coupled with Volume of Fluid (VOF) method in a 6 m horizontal pipe with 0.050 m inner diameter. Dynamic pressure readings were collected at a strategic location and were converted to scalograms to be used as inputs in deep learning architectures like ResNet-50 and ShuffleNet. Both architectures performed effectively in classifying different flow regime and recorded testing accuracies of 85.7% and 82.9% respectively. According to our knowledge no similar research has been reported in literature, where various Convolutional Neural Networks are used along with dynamic pressure signals to identify flow regime in horizontal pipe.

The power of paired proximity science observations: Co-located data from SHERLOC and PIXL on Mars

We present a synthesis of PIXL elemental data and SHERLOC Raman spectra collected on two targets investigated by the Perseverance rover during the first year of its exploration of Jezero Crater, Mars. The Bellegarde target (in the Máaz formation) and Dourbes target (in the Séítah formation) exhibit distinctive mineralogies that are an ideal case study for in situ analysis by SHERLOC and PIXL. Each instrument alone produces valuable data about the chemistry and spatial distribution of mineral phases at the sub-millimeter scale. However, combining data from both instruments provides a more robust interpretation that overcomes the limitations of either instrument, for example: 1) Detection of correlated calcium and sulfur in Bellegarde by PIXL is corroborated by the co-located detection of calcium sulfate by SHERLOC. 2) Detection of sodium and chlorine in Dourbes is consistent with either chloride or oxychlorine salts, but SHERLOC does not detect perchlorate or chlorate. 3) A Raman peak at 1120 cm−1 in Dourbes could be sulfate or pyroxene, but elemental abundances from PIXL at that location are a better match to pyroxene. This study emphasizes the importance of analyzing co-located data from both instruments together, to obtain a more complete picture of sub-millimeter-scale mineralogy measured in situ in Jezero crater, Mars, by the Perseverance rover.

Towards realistic modeling of mineral microstructures

The microstructures of mineral materials determine their mineral processing characteristics. Realistic microstructure models are a precondition for simulations of various mineral processing steps. For this reason, a model for simulating the microstructure of minerals that consists of densely packed grains of various phases is presented. It is based on geometrical information and image analysis of planar sections of samples of the material of interest. This includes grain size characteristics, frequencies of mineral components, and information on the spatial distribution of phases. The simulation is carried out by a sequential algorithm, which adds stepwise new grains to an incomplete microstructure. The final result is a tessellation of irregular non-convex grains of spatially variable components. The application of the model is demonstrated for a sample of granite material. A goodness-of-fit test shows that in this case the model is indeed realistic.

Chemical reactions of carbonate-rich mudstones with aqueous CO2 and their impacts on rock's local microstructural and chemo-mechanical properties

Assessment of the structural integrity of carbonate-rich rocks subjected to acidic brine strongly relies on the understanding of the coupling between the chemical changes and the alteration of the mechanical properties of rocks. This study aims at an integrated microscale chemo-mechanical and microstructural characterization of carbonate mudstones exposed to CO2-rich brine under high pressure and high temperature conditions. Digital image analysis was performed on X-ray micro-computed tomography (micro-CT) images to realize microstructural evolution and spatial distribution of pores and different material phases. This approach showed three distinct regions of porosity and carbonate content (resulting from dissolution and precipitation of calcium carbonates), which are critical for understanding the mechanical alteration of the rocks being investigated. Detailed analysis of the micro-CT images also revealed the preferred precipitation of calcium carbonates in pores parallel to the flow/reaction direction. Microscale chemo-mechanical testing performed using coupled grid nanoindentation and scanning electron microscopy-energy dispersive spectrometry (SEM-EDS) complemented the micro-CT results: dissolution zones close to the reacted surface were found to have lower hardness and indentation modulus while an increased values in adjacent precipitation zones was observed. Also, the thickness of the precipitation zones was found to be considerably higher in the direction of the bedding planes, which needs special attention in laminated rocks like shales and mudstones. The microstructural and mechanical properties of the microscale regions and the layered structure are expected to influence the overall mechanical properties and integrity of the rock. These results enhance our understanding of the microscale origin of the macroscopic mechanical alteration of carbonate-rich mudstones subjected to acidic brine.

A comprehensive strategy for exploring corrosion in iron-based artefacts through advanced Multiscale X-ray Microscopy

The best strategy to tackle complexity when analyzing corrosion in iron artefacts is to combine different analytical methods. Traditional techniques provide effective means to identify the chemistry and mineralogy of corrosion products. Nevertheless, a further step is necessary to upgrade the understanding of the corrosion evolution in three dimensions. In this regard, Multiscale X-ray Microscopy (XRM) enables multi-length scale visualization of the whole object and provides the spatial distribution of corrosion phases. Herein, we propose an integrated workflow to explore corrosion mechanisms in an iron-nail from Motya (Italy) through destructive and non-destructive techniques, which permit the extraction of the maximum information with the minimum sampling. The results reveal the internal structure of the artefact and the structural discontinuities which lead the corrosion, highlighting the compositional differences between the tip and the head of the iron nail.

New insight on spatial localization and microstructures of calcite-aragonite interfaces in adult shell of Haliotis tuberculata: Investigations of wild and farmed abalones by FTIR and Raman mapping

In the present study, we investigated the shell microstructures of the gastropod European abalone Haliotis tuberculata in order to clarify the complex spatial distribution of the different mineral phases. Our studies were carried out with a standardized methodology on thirty adult European abalone H. tuberculata (5–6 cm long) composed of 15 wild individuals and 15 individuals taken from the France Haliotis hatchery. The macroscopic (binocular) and microscopic observations coupled with Fourier Transform Infrared Spectroscopy (FTIR) and Raman vibrational analysis allowed to unambiguously detect, identify and localize calcite and aragonite. For the first time it has been shown that calcite is present in 100% of farmed and wild adult shell. The microstructural details of the calcite-aragonite interfaces were revealed by using both confocal micro-Raman mapping and Scanning Electron Microscopy (SEM) observations. Calcite zones are systematically found in the spherulitic layer without direct contact with the nacreous layer. The calcite area - nacreous layer interface is made of a thin spherulitic layer with variable thickness from a few micrometers to several millimeters.In order to contribute to a better understanding of the biomineralization process, a model explaining the hierarchical arrangement of the different phases of calcium carbonate is presented and discussed. Finally, it has been shown that these calcitic zones can be connected to each other within the shells and that their spatial distributions correspond to streaks perpendicular to the direction of length growth.

A Pattern Processing Method to Map Nanoscale Phases by EBSD.

The crystallographic analysis of nanoscale phases with dimensions well below the spatial probing volume of electron backscatter diffraction (EBSD) traditionally rely on electron microscopy in transmission (either in SEM or TEM), because EBSD patterns are invariably dominated by the matrix phase contribution and present seemingly no trace from such nanoscale phases. Yet, this study shows that such nanoscale features generate a very faint but valuable secondary diffraction signal which can be retrieved. A diffraction pattern postprocessing method is presented which focuses on the detection of such secondary signal emitted by nanoscale minority phases in overlapped patterns dominated by a dominant matrix signal. The predominant, majority phase contribution in EBSD patterns is removed by a close-neighbor pattern subtraction routine, after which both the conventional Hough indexing method as well as pattern matching methods can be used to reveal the crystallography, spatial distribution, morphology, and orientation of nanoscale minority phases initially absent from EBSD maps. Nanolamellar pearlitic steel, which has long been out of reach for EBSD, has been chosen as an application example.

Microstructural characterization of as-fabricated monolithic plates with boron carbide, aluminum boride, and zirconium boride burnable absorbers

• Fabrication of aluminum-based research reactor plates containing boron-based burnable absorbers. • Scanning electron microscopy. • Transmission electron microscopy. • Burnable absorber size and shape distribution analysis. The use of burnable absorbers can be beneficial for nuclear reactors by extending the fuel's operational cycle, providing additional criticality control, and flattening the power profile. In this work, three burnable absorber materials (boron carbide, aluminum boride, and zirconium boride) embedded in aluminum have been fabricated into foils and clad in AA-6061 for potential use in high performance research reactors. The as-fabricated boron-containing phases were determined using transmission electron microscopy to be AlB 2 , B 4 C, and ZrB 2 . TEM also revealed incomplete bonding at the B 4 C-matrix interface. SEM showed a relatively uniform spatial distribution of boron-containing phases for all the candidate materials. Higher porosity was observed in the foil containing ZrB 2 in its as-rolled condition. The porosity in the ZrB 2 foil was reduced by hot isostatic pressing. The size and shape distributions of the boron-containing phases were analyzed on the criteria of cross-sectional area, perimeter, roundness, circularity, and aspect ratio. A method of converting the 2D burnable absorber dispersoids seen in cross-sectional microscopy images into 3D volumes was derived using both spherical and ellipsoidal geometry models. The difference in calculated burnable absorber dispersoid average volume between the two models ranges from 20% to 100%, which could impact burnable absorber burnout rates due to differences in neutron self-shielding.

Manipulating Color Emission in 2D Hybrid Perovskites by Fine Tuning Halide Segregation: A Transparent Green Emitter.

Halide perovskite materials offer an ideal playground for easily tuning their color and, accordingly, the spectral range of their emitted light. In contrast to common procedures, this work demonstrates that halide substitution in Ruddlesden-Popper perovskites not only progressively modulates the bandgap, but it can also be a powerful tool to control the nanoscale phase segregation-by adjusting the halide ratio and therefore the spatial distribution of recombination centers. As a result, thin films of chloride-rich perovskite are engineered-which appear transparent to the human eye-with controlled tunable emission in the green. This is due to a rational halide substitution with iodide or bromide leading to a spatial distribution of phases where the minor component is responsible for the tunable emission, as identified by combined hyperspectral photoluminescence imaging and elemental mapping. This work paves the way for the next generation of highly tunable transparent emissive materials, which can be used as light-emitting pixels in advanced and low-cost optoelectronics.

Assessment of compositional changes of carbonated cement pastes subjected to high temperatures using in-situ Raman mapping and XPS

This paper presents a new method for assessing the compositional changes of carbonated cement pastes subjected to high temperatures. In this new method, in-situ Raman mapping combined with X-ray photoelectron spectroscopy (XPS) was used to monitor the phase transformation in carbonated cement pastes subjected to various high temperatures from 30 to 950 °C. Two kinds of carbonated areas, i.e., vaterite dominated and calcite dominated, were found in the in-situ Raman measurements. With the elevation in temperature, most of the vaterite was converted to calcite at 500 °C and completely decomposed at 600 °C, while the decomposition of calcite started at 600 °C and finished at 720 °C. Meanwhile, the depolymerization of the calcium modified silica gel to the silicate phases with a lower degree of polymerization was initiated at 500 °C, which led to the crystallization of β-C2S at 600 °C. The generation of β-C2S was found to increase with the elevation in temperature and became the dominant phase at 950 °C. In conclusion, the high temperature could affect the stability of carbonated cement pastes at 500 °C and above. The in-situ Raman mapping measurement has provided an extraordinary view of the spatial distribution of interesting phases subjected to high temperatures in a non-destructive way, which should be more consistent with the true condition in the material.

Compositional heterogeneity in multiphase steels: Characterization and influence on local properties

Local variations in chemical composition, i.e., compositional heterogeneities, play an important role in the thermodynamic stability and spatial distribution of phases in multiphase steels. The influence of heterogeneous elemental distribution on the resulting local microstructure and mechanical properties has been investigated in the present work. Two steels, one with dual-phase (DP) and one with complex-phase (CP) microstructure, were fabricated from the same cast but differently heat treated in the intercritical annealing regime to yield variations in local microstructure formation. The heterogenous distribution of C and Mn that exists on different length scales are quantified by a characterization approach correlating local chemistry, microstructure, and hardness by using electron probe microanalysis (EPMA), electron backscattered diffraction (EBSD), and nanoindentation. Mn was alternately enriched and depleted in bands parallel to the rolling direction caused by segregation during continuous casting. The local C content was closely associated with the spatial phase distribution resulting from intercritical annealing. In the DP steel, the heterogeneity of C distribution was more pronounced and martensite inherited from the Mn banding due to the lower intercritical annealing temperature. On the other hand, the CP steel, heat treated at higher intercritical annealing temperature, exhibited a more homogenous C distribution resulting in a homogeneous distribution of martensite. In addition to their varying partitioning into the present phases, C and Mn in large martensite islands tended to concentrate in the vicinity of phase interfaces and deplete in the center. Furthermore, chemical boundaries with the smooth transition in local properties were observed in the CP steel. The Mn segregation bands and their impact on martensite morphology and location is reflected by the local hardness distribution. The correlation between compositional heterogeneity, microstructure formation, and microscopic as well as macroscopic mechanical properties is discussed in detail.

Characterization of the Convoluted 3D Intermetallic Phases in a Recycled Al Alloy by Synchrotron X-ray Tomography and Machine Learning

Fe-rich intermetallic phases in recycled Al alloys often exhibit complex and 3D convoluted structures and morphologies. They are the common detrimental intermetallic phases to the mechanical properties of recycled Al alloys. In this study, we used synchrotron X-ray tomography to study the true 3D morphologies of the Fe-rich phases, Al2Cu phases and casting defects in an as-cast Al-5Cu-1.5Fe-1Si alloy. Machine learning-based image processing approach was used to recognize and segment the different phases in the 3D tomography image stacks. In the studied condition, the β-Al9Fe2Si2 and ω-Al7Cu2Fe are found to be the main Fe-rich intermetallic phases. The β-Al9Fe2Si2 phases exhibit a spatially connected 3D network structure and morphology which in turn control the 3D spatial distribution of the Al2Cu phases and the shrinkage cavities. The Al3Fe phases formed at the early stage of solidification affect to a large extent the structure and morphology of the subsequently formed Fe-rich intermetallic phases. The machine learning method has been demonstrated as a powerful tool for processing big datasets in multidimensional imaging-based materials characterization work.