The equimolar AlCoCrFeNi high entropy alloy (HEA) was printed by selective laser melting (SLM), with emphasis on its densification, phase identification, non-equilibrium microstructure and ...properties. The density of SLM samples increase gradually with the increase of volumetric energy density (VED) with the maximal relative density 98.4%. SLM samples are consisted of disordered body-center cubic phases (A2) and ordered body-center cubic phases (B2) which are different from the conventional cast or deformation with A2 and fcc phase; the content of B2 phase increases with the VED. Interestingly, the Fe-Cr precipitate, which has never been found in the cast one, is observed in the SLM one without heat treatment. The microstructure of SLM samples shows epitaxial growth of columnar A2 grain bundles perpendicular to the melt pool boundary with an average grain size of about 1.5 μm; the B2 phase is between the columnar A2 grains. At low VED, the SLM sample shows preferred orientation, and is gradually transformed to the crystallographic direction families at a higher VED. Besides, there exists the {100}A2∥{100}B2 orientation relationship in A2 and B2 phase. The maximal micro-hardness of 632.8Hv of SLM sample is higher than the cast one and the electron beam melting printed one.
•The equiatomic AlCoCrFeNi alloy was successfully printed by SLM.•The A2 and B2 phase were identified by EBSD.•The Fe-Cr precipitate was found in the SLM samples.•The micro-hardness of SLM samples reaches 632Hv.
Several methods have been developed to assess the thermal state of the mantle below oceanic ridges, islands, and plateaus, on the basis of the petrology and geochemistry of erupted lavas. One leads ...to the conclusion that mantle potential temperature (i.e., TP) of ambient mantle below oceanic ridges is 1430°C, the same as Hawaii. Another has ridges with a large range in ambient mantle potential temperature (i.e., TP = 1300–1570°C), comparable in some cases to hot spots (Klein and Langmuir, 1987; Langmuir et al., 1992). A third has uniformly low temperatures for ambient mantle below ridges, ∼1300°C, with localized 250°C anomalies associated with mantle plumes. All methods involve assumptions and uncertainties that we critically evaluate. A new evaluation is made of parental magma compositions that would crystallize olivines with the maximum forsterite contents observed in lava flows. These are generally in good agreement with primary magma compositions calculated using the mass balance method of Herzberg and O'Hara (2002), and differences reflect the well‐known effects of fractional crystallization. Results of primary magma compositions we obtain for mid‐ocean ridge basalts and various oceanic islands and plateaus generally favor the third type of model but with ambient mantle potential temperatures in the range 1280–1400°C and thermal anomalies that can be 200–300°C above this background. Our results are consistent with the plume model.
Background
In-situ
micro-computed tomography (µCT) technology is an attractive approach to investigate the evolution process of damage inside ceramic matrix composites (CMCs) during high-temperature ...service. The evolution process is highly time-sensitive under temperature-induced loads, and fast scanning is very necessary for
in-situ
µCT tests.
Objective
The objective of this work is to provide a fast scanning method for in situ µCT tests on CMCs with complex microstructures by the innovation of a reconstruction algorithm.
Method
To overcome the severe degradation of the reconstructed image quality resulting from sparse CT scans, a deep-learning-based multi-domain sparse reconstruction method was proposed. Three sub-networks including the projection-domain, image-domain, and fusion network were constructed in the multi-domain method to make full use of the information from the projection and image domain.
Results
The proposed deep-learning-based sparse reconstruction method provided satisfactory µCT images on C/SiC composites with acceptable quality. The scanning time was reduced by 6 times. All selected evaluation metrics of the proposed method are higher than those of other single-domain methods and traditional iterative method. The segmentation accuracy of the µCT images obtained by the proposed method can meet the subsequent quantitative analysis. An
in-situ
tensile test of CMCs is conducted to further evaluate the performance in the practical application of
in-situ
experiments. The results indicate that the weak and thin micro-cracks can still be effectively retained and recovered. A detailed workflow to implement the method generally is also provided.
Conclusions
Based on the deep-learning-based multi-domain sparse reconstruction method, the process of
in-situ
µCT tests can be greatly accelerated with little loss of the reconstructed image quality.
All-perovskite oxide heterostructure of SrSnO3/Nb-doped SrTiO3 was fabricated by using the pulsed laser deposition method. Unusual transport properties of the interface between SrSnO3 and Nb-doped ...SrTiO3 have been investigated at temperatures from 100 to 300 K. A diodelike rectifying behavior has been demonstrated by the temperature-dependent current–voltage (IV) measurements. The forward current showed typical IV characteristics of p–n junctions or Schottky diodes and was perfectly fitted using the thermionic emission model. At the reverse bias, however, the temperature-dependent IV curves developed in the opposite direction, indicating the tunneling effects on the interface. The Poole–Frenkel emission was used to explain this electrical transport mechanism under the reverse voltages.
Bright and eclipsing, the high-mass X-ray binary Vela X-1 offers a unique opportunity to study accretion onto a neutron star from clumpy winds of O/B stars and to disentangle the complex accretion ...geometry of these systems. In Chandra-HETGS spectroscopy at orbital phase ~0.25, when our line of sight towards the source does not pass through the large-scale accretion structure such as the accretion wake, we observe changes in overall spectral shape on timescales of a few kiloseconds. This spectral variability is, at least in part, caused by changes in overall absorption and we show that such strongly variable absorption cannot be caused by unperturbed clumpy winds of O/B stars. We detect line features from high and low ionization species of silicon, magnesium, and neon whose strengths and presence depend on the overall level of absorption. These features imply a co-existence of cool and hot gas phases in the system, which we interpret as a highly variable, structured accretion flow close to the compact object such as has been recently seen in simulations of wind accretion in high-mass X-ray binaries.
Ruminant production systems are important contributors to anthropogenic methane (CH4) emissions, but there are large uncertainties in national and global livestock CH4 inventories. Sources of ...uncertainty in enteric CH4 emissions include animal inventories, feed dry matter intake (DMI), ingredient and chemical composition of the diets, and CH4 emission factors. There is also significant uncertainty associated with enteric CH4 measurements. The most widely used techniques are respiration chambers, the sulfur hexafluoride (SF6) tracer technique, and the automated head-chamber system (GreenFeed; C-Lock Inc., Rapid City, SD). All 3 methods have been successfully used in a large number of experiments with dairy or beef cattle in various environmental conditions, although studies that compare techniques have reported inconsistent results. Although different types of models have been developed to predict enteric CH4 emissions, relatively simple empirical (statistical) models have been commonly used for inventory purposes because of their broad applicability and ease of use compared with more detailed empirical and process-based mechanistic models. However, extant empirical models used to predict enteric CH4 emissions suffer from narrow spatial focus, limited observations, and limitations of the statistical technique used. Therefore, prediction models must be developed from robust data sets that can only be generated through collaboration of scientists across the world. To achieve high prediction accuracy, these data sets should encompass a wide range of diets and production systems within regions and globally. Overall, enteric CH4 prediction models are based on various animal or feed characteristic inputs but are dominated by DMI in one form or another. As a result, accurate prediction of DMI is essential for accurate prediction of livestock CH4 emissions. Analysis of a large data set of individual dairy cattle data showed that simplified enteric CH4 prediction models based on DMI alone or DMI and limited feed- or animal-related inputs can predict average CH4 emission with a similar accuracy to more complex empirical models. These simplified models can be reliably used for emission inventory purposes.
Laser cladding of Fe-20Cr-10Ni-2Si alloy usually faces challenge of metallurgical defects like micropores and interdendritic fragile precipitates. In this paper, the laser cladding combined with ...friction stir processing (FSP) was applied to deal with this problem and prepare the nanostructured Fe-20Cr-10Ni-2Si alloy layer. The coarse dendritic grains (5 ~ 10
μ
m) of laser processed Fe-20Cr-10Ni-2Si alloy were broken into nanocrystallines which contain uniformly distributed nanoparticles (5 ~ 400 nm) in the deformation zone by FSP. The gradient microstructure with an average grain size of several nanometers on the top surface to several micrometers in the center part was obtained by FSP. Meanwhile, the grain size in the plastic zone decreases as the rotary speed rises. Grain refinement by FSP results in the increase of microhardness from 323 HV up to 583 HV, decreasing the friction coefficient from 0.42 to 0.35 and thus the wear resistance is improved.
Al2O3 ceramic was reliably joined to TiAl alloy by active brazing using Ag–Cu–Ti filler metal, and the effects of brazing temperature, holding time, and Ti content on the microstructure and ...mechanical properties of Al2O3/TiAl joints were investigated. The typical interfacial microstructure of joints brazed at 880°C for 10min was Al2O3/Ti3(Cu,Al)3O/Ag(s.s)+AlCu2Ti+Ti(Cu,Al)+Cu(s.s)/AlCu2Ti+AlCuTi/TiAl alloy. With increasing brazing temperature and time, the thickness of the Ti3(Cu,Al)3O reaction layer increased, and the blocky AlCu2Ti compounds aggregated and grew gradually. The Ti dissolved from the TiAl substrate was sufficient to react with Al2O3 ceramic to form a thin Ti3(Cu,Al)3O layer when Ag–Cu eutectic alloy was used, but the dissolution of TiAl alloy was inhibited with an increase in Ti content in the brazing filler. Ti and Al dissolved from the TiAl alloy had a strong influence on the microstructural evolution of the Al2O3/TiAl joints, and the mechanism is discussed. The maximum shear strength was 94MPa when the joints were brazed with commercial Ag–Cu–Ti filler metal, while it reached 102MPa for the joint brazed with Ag–Cu+2wt% TiH2 at 880°C for 10min. Fractures propagated primarily in the Al2O3 substrate and partially along the reaction layer.
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