查看更多>>摘要：? 2022Understanding the metallurgical joinability of pure Mg and pure Fe and their interfacial microstructure lays the foundation for deciphering the complicated mechanism of joining various magnesium alloys and steels in applications. Pure Mg and pure Fe were successfully joined to form a metallurgical bond for the first time using the friction stir assisted scribe technique. Through detailed characterization, we found that the two immiscible metals are bonded by a critical interfacial oxide layer that spans only ~40 ± 10 nm. We present the first direct experimental evidence of the presence of an Mg/Fe oxide-rich interfacial layer using high-resolution electron microscopy and discuss the contribution of oxide formation toward a successful joining mechanism.
查看更多>>摘要：? 2022 The AuthorsGas atomized Nd-Fe-B powders of several compositions were separated in different size fractions by sieving. These fractions were annealed between 1100 °C and 1150 °C for 24 and 96 h. The oxygen content of the powders was measured before and after annealing for the different size fractions. The oxygen concentration of the powders depends strongly on the particle size and increases significantly during annealing, particularly in the case of small particle sizes. The effect of particle size on the microstructural changes was analyzed in detail, particularly on grain growth, using high resolution scanning electron microscopy and transmission electron microscopy. Electron back scattering diffraction was used to measure grain size. When the particle size rises, the degree of sintering decreases and the higher solid/vapor surface area reduces the mobility of grain boundaries. Oxidation also reduces grain growth rate and its effect is more evident for particles sizes below 45–63 μm and high Nd concentrations. Nb addition leads to the formation of intra- and intergranular precipitates. The size of these Nb-Fe-containing precipitates increases with the particle size for equivalent annealing conditions. At 1150 °C, Nb loses its effect as an inhibitor of grain growth in the particle size fractions larger than 45–63 μm.
查看更多>>摘要：? 2022 The AuthorQuality metrics of electron backscatter diffraction patterns were constituted with a few descriptors of the characteristic intensity distribution across diffraction bands. The image contrast by these metrics was compared quantitatively with a ferritic-martensitic dual phase steel. The metrics which described the sharpness of bands were superior to those that represented the contrast from a background intensity. In addition, the ones that were defined around the edges of a band presented better contrast than those in the interior. Pattern degradation by martensite was approximated with lattice rotations in an interaction volume, and the sensitivity of the metrics to pattern degradation accords well with their behavior on the experimental patterns. The metrics defined around the band edges were more prone to instability in the evaluation processes. A new metric which described the sharpness in the interior of bands presented a compromise between the sensitivity and the stability.
查看更多>>摘要：? 2022 Elsevier Inc.A novel Nb-Ti micro-alloyed medium-Mn steel was proposed and subjected to austenite reverted transformation annealing process. The suitable annealing process involving intercritical annealing at 690–700 °C for 5 h was summarized by means of thermodynamic and kinetic calculation, which was proved to provide good guidance for the experiment. The 700 °C annealed steel was characterized by a dual-phase microstructure consisting of ultra-fine grained tempered martensite and retained austenite. Both blocky and lath-like retained austenite with volume fraction of 37.4% and moderate stability was obtained. Moreover, a large number of spherical TiC and rod-like (Nb,Ti)C precipitates were observed, which increased the yield strength significantly. The transformation-induced plasticity (TRIP) effect of retained austenite and precipitation strengthening of nano-sized precipitates were combined in the studied steel, resulting in excellent trade-off between yield strength, tensile strength and total elongation. The yield strength, tensile strength, uniform elongation and total elongation was 785 MPa, 1015 MPa, 32.3% and 42.5%, respectively. The product of tensile strength and uniform elongation was up to 32.78 GPa%, which was superior to that of low-alloy steels, TRIP steels and Q&P steels, and was comparable with some high-Mn high-Al steels.
查看更多>>摘要：? 2022 Elsevier Inc.The main problem during preparing high porosity ceramics via aqueous gel-casting is the large drying shrinkage of green bodies. In this work, carbon fibers with high aspect ratio were introduced into aqueous gel-casting processes, which significantly inhibited the drying shrinkage of green bodies by overlapping fibers. At the same time, exhaustible carbon fibers sintered in air also act as sacrificial templates to further improve the porosity. Through the above method, porous LAS/SiC ceramics with high porosity and near-zero expansion were prepared. Drying shrinkage of the green bodies was reduced from 25.2% to 5.7% with the increase of fibers. The porosity of the obtained LAS/SiC ceramic is as high as 76.2%. When the fibers content is 20 vol% and LAS to SiC volume ratio is 6: 4, the composite has maximum value of compression and bending strength (18.2 and 14.0 MPa) and near-zero CTE (0.9 × 10?6 /K).
查看更多>>摘要：? 2022 Elsevier Inc.The influences of heat treatment on the microstructure, domain structure and magnetic characteristics of the Fe73.5Si15.5B7Cu1Nb3 alloy were investigated. We demonstrated that the as-spun alloy exhibits high amorphous forming ability and good thermal stability with a large annealing interval between the primary and secondary crystallization peaks over 170 °C. Also, the interaction of chemical concentration fluctuations and heterogeneous nucleation is responsible for the nanocrystallization mechanism of alloy. Furthermore, the magnetic structures change from the narrow and zigzag-like branched domains to wide and regular striped domains with increasing annealing temperature, which leads to a decrease in pinning effects. Appropriate magnetic anisotropy introduced by heat-treatment process has effect on the magnetic mechanism and the shape of magnetic hysteresis loops, which adjusts the frequency characteristics. After the optimum annealing, the alloy exhibits the excellent magnetic properties including high Ms. of 135.4 emu/g and low Hc of 0.56 A/m, together with good low-frequency characteristics.
查看更多>>摘要：? 2022 Elsevier Inc.7A85 aluminum alloy forgings were compressed at 10% to 30% deformation at room and cryogenic temperatures, followed by solid-solution treatment, water quenching, 3% cold deformation, and two-stage aging. The results indicated that cryogenic deformation increased coarse second-phase particle fragmentation and led to massive dislocation proliferation, which facilitated particle dissolution due to the formation of more interfaces and dislocation-promoted dissolution. These increased the driving force for aging precipitation and produced denser matrix precipitates and narrower grain boundary precipitate-free zones. Meanwhile, numerous dislocations provided more nucleation sites for recrystallization and thus refined grains during solution treatment. The grains were refined from 500 μm in the undeformed state to an average size of 35 μm under 20% cryogenic deformation. The excessive dislocation energy and stored deformation energy at 30% deformation caused recrystallized grain growth. The optimal mechanical properties were obtained at 20% cryogenic deformation with an ultimate tensile strength, yield strength, and elongation of 499 MPa, 435 MPa, and 13.1%, which were respectively 1.6%, 2.1%, and 37.9% higher than those of the undeformed sample.
查看更多>>摘要：? 2022 Elsevier Inc.Heterostructured TiO2/In2O3 nanowires have been extensively applied in various photonic devices; their performance is highly related to the microstructures, which has not been, however, clearly understood; thus, it is important to investigate the microstructural evolution of the material during processing. In this work, the crystallinity and microstructure of TiO2/In2O3 nanowires were successfully controlled with the variation of annealing temperatures via solid-state reactions. The dynamic phase transformation process was demonstrated by in situ transmission electron microscope (TEM). Moreover, the elemental information at different states was identified by energy dispersive spectroscopy (EDS). It is found that different annealing temperatures would contribute to different solid-state reactions and nanowire heterostructures. Additionally, photoresponse studies show characteristics enhancement for such nanoheterostructures. This study provides the knowledge of the fundamental science in kinetics of heterostructured nanostructures, which benefits the improvement of the performance for future photonic applications.
查看更多>>摘要：? 2022 Elsevier Inc.The CoCrFeNiAl0.3 high entropy alloy samples were produced by different ball milling strategies including mechanical mixing and mechanical alloying in combination with spark plasma sintering and hot extrusion. The microstructure evolution and phase formation were investigated in correlation to tensile mechanical properties. It was found that a mixture of FCC and BCC structured matrix, as well as intermediate multiphases (e.g., Cr-rich σ phase, B2-NiAl, L12-Ni3Al) were formed because of incomplete alloying during consolidation of the mechanically mixed powders. After homogenization treatment at 1423 K, a complete alloyed FCC matrix was formed due to the transformation from BCC to FCC as well as the dissolution of the intermediate phases. For the mechanically alloyed powders, a similar single phase FCC matrix with an averaged grain size of 784 nm was obtained when subjected to thermomechanical consolidation. The microstructure exhibited a good thermal stability (grain size: 789 nm) even after homogenization treatment, which was likely attributed to the pinning effects of the dispersed Al2O3 nanoparticles deriving from the in-situ reaction of Al and O during powder consolidation. The Al2O3 nanoparticles played a dominate role in tailoring the microstructure and then enhanced the mechanical properties by Orowan mechanism, leading to a good combination of yield strength and elongation to fracture of 950 MPa and 17.3%, respectively.
查看更多>>摘要：? 2022Holographic and near-field ptychographic X-ray computed tomography techniques have been compared by characterizing a typical solid oxide cell hydrogen electrode using a high-energy X-ray beam. The main advantages and drawbacks of both methods are discussed regarding the possibility to image the Ni-YSZ cermet, a complex porous electrode microstructure composed of X-ray absorbent materials. The same innovative sub-pixel alignment algorithm, based on tomographic consistency, was applied to align the different tomographic projections for each technique. It has been shown that a better signal-to-noise ratio (SNR) is obtained using near-field ptychographic tomography, whereas holographic tomography can be faster with similar spatial resolution. Moreover, quantitative electron density maps have been obtained with the two techniques. The quality of the phase identification has also been assessed and compared in both cases using a classical grey-level class separability criterion. After the segmentation, a set of typical microstructural properties describing the electrode morphology was computed. The comparison of the results allowed validating the complementarity of the two X-ray imaging techniques. Despite the more time-consuming data acquisition and processing than holographic tomography, near-field ptychographic tomography is especially well adapted to image samples without any insight on their composition or when the sample is highly absorbent. Yet, holographic X-ray tomography, using high-energy X-rays to reduce the sample absorption, remains a faster 3D imaging technique with spatial resolution and contrast sensitivity sufficient for the characterization of solid oxide cell materials.
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