查看更多>>摘要：? 2022 Elsevier Inc.CdZnTe (CZT) has attracted much attention in nuclear detection field attribute to its high detection efficiency, high energy resolution and room-temperature operation. In this work, the CdZnTe samples were prepared by Vertical gradient method. High-resolution transmission electron microscopy (HRTEM) was used to investigate the nanoscale defects in CZT crystals. It is found that the twins are symmetric about the {111} plane, and the dislocations and stacking faults locate around the twin boundary. Te precipitations with hexagonal crystal structure is coherent with the CZT matrix. Te precipitated phases have three shapes of hexagon, polygon and irregularity, which determined by the interface energy between precipitations and matrix. The ordered phase with acicular shapes was found along [011] zone axis. The two variants of the ordered phase is corresponding to 1/211ˉ1 and 1/31ˉ11 ultrasound lattice, respectively. Besides the small angle grain boundaries with semi-coherent interface are observed. It is important to explore the behavior of nanoscale defects in the growth of CZT crystals in order to enlighten a path to regulate the nanoscale defects. The stability of the temperature interface is crucial to the preparation of high quality CZT crystals.
查看更多>>摘要：? 2022 Elsevier Inc.Martensitic and nanobainite transformations are studied in situ in a low alloyed, high-Si steel by using in situ HEXRD, combined with dilatometry and SEM observations, and by considering the same steel composition and austenitization conditions. The martensitic microstructure presents a mixed lath-plate morphology with large scatter of sizes whereas the bainite microstructure shows finer laths with more uniform sizes. Recently introduced methods are used to track in situ by HEXRD, in one single experiment, the phase fractions, the distribution of the carbon and the evolution of the dislocation densities. The study of nanobainite revealed that about two thirds of the carbon partitions from the ferrite to precipitate into transition iron carbides or to enrich the austenite. Both processes occur very fast after the formation of each nanobainite lath, but the ferrite remains largely supersaturated in carbon. The dislocation density increases inside each new forming bainitic ferrite lath. It then decreases when recovery becomes preponderant, as described with a recovery model from the literature. After the martensitic transformation, the retained austenite ends up with high hydrostatic compressive stresses. Dislocation densities are higher than in nanobainite and probably more heterogeneous, because recovery is less significant. No carbides were detected, contrary to the nanobainite. The carbon mass balance is analyzed in the light of these new results and previous investigations on similar systems.
查看更多>>摘要：? 2022 The AuthorsNanostructured films offer the ability of modifying surface properties, even more, when they can generate layers with controlled porosity. The lower implicit integrity of these (multi)layers when compared to their compact counterparts, hinders the attainment of electron-transparent sections of submicron thicknesses (lamellae), which becomes one of the main reason for the scarcity of studies thorough (scanning-)transmission electron microscopy ((S)TEM). Aware of this opportunity, this report provides an overview of the possibilities offered by the application of a variety of (S)TEM techniques for the study of nanostructured and porous photonic surfaces. A few working examples are presented to illustrate the type of information that can be obtained in the case of mesoporous films prepared either by at oblique angles physical processes as well as nitride nanowire arrays prepared by epitaxy methods. It will be demonstrated that this approach enables the realization of several pioneering works, which are essential to complete the characterization of such porosity-controlled coatings. Topics as diverse as the preparation of electron-transparent specimens and the advanced characterization of their structures, morphologies, interfaces and compositions are addressed thanks to the implementation of new breakthroughs in (S)TEM, which allow to obtain high-resolution imaging, spectroscopies, or tomography, at both microscopic and nanoscopic levels. Finally, establishing (S)TEM as a reference tool for the advanced structural, chemical and morphological characterization of porous nanostructured skins, will open new horizons, providing better and new insights and thus allowing the optimization of the fabrication and design of such architectures.
查看更多>>摘要：? 2022 The Author(s)To attain the desired mechanical properties of an additively manufactured component, robust post-processing in term of thermal treatment is highly required to reduce the crystallographic anisotropy. However, the microstructure appearance with respect to the post-treatment temperature is not well understood mechanistically. In this study, the microstructural evolution of grains of a laser-powder bed fused (L-PBF) nickel-base superalloy, CM247LC, during post-processing heat treatment is investigated systematically. Recrystallization barely happens below the γ' solvus temperature leading to a remaining unhomogenized dendritic(cellular) structure. However, recrystallization is introduced above the γ' solvus temperature. By considering the grain boundary (GB) migration mechanisms and supported by experimental observations, the sluggish recrystallization behavior of this γ'-strengthened nickel-based superalloy has been understood. Owing to lack of the difference in stored energy between adjacent grains, this primary driving force is constrained. The GB migration is majorly driven by capillarity force (1–10 MPa) before the recrystallization occurrence, which is evident by the evolution of GB curvatures. On the other hand, the Zener pinning force generated from GB precipitates including carbides and γ' precipitates provides the dragging force in the comparable scale (1–10 MPa) against the GB migration.
查看更多>>摘要：? 2022The microstructure and the room-temperature tensile property of a γ-Ti–45Al–8.5Nb–(W, B, Y) alloy after different heat treatments have been investigated. The results show that the α2′ martensite plate and columnar α2 Widmanstatten microstructure with a small number of remnant B2 phase can be obtained for the γ-Ti–45Al–8.5Nb–(W, B, Y) alloy by water-quenching and air-cooling, respectively from the β phase field. The B2 phase with weak Nb enrichment retained from the β phase field can be removed easily after subsequent heat-treatment at 1340 oC for 3 h, which produces a fine lamellar α2 + γ microstructure in the alloy. The alloy subjected to a two-step heat-treatment (1450 oC followed by air-cooling/1340 oC followed by furnace-cooling) shows better tensile properties with an ultimate tensile strength of 826–850 MPa and a total elongation of 0.95–1.37% than the as-received alloy. The improved tensile properties can be attributed to microstructure refinement and reduction of remnant B2 phase located at lamellar colony boundaries in the γ-Ti–45Al–8.5Nb–(W, B, Y) alloy.
查看更多>>摘要：? 2022 Elsevier Inc.Variant selection, a common but complex phenomenon in Ti alloys, is not only governed by microstructural characteristics that affect the nucleation process of variants, such as grain orientation, grain boundaries, and residual α phase, but also remarkably influenced by some kinetic factors, such as cooling rate and residual stress, especially for the additive manufactured Ti alloys. To determine the influence of cooling rates on variant selection of laser solid formed (LSF) Ti-6Al-4V alloys, the selection of α variant in different zones of LSFed samples (possessing different cooling rates) but belonging to one single β grain was systematically studied. With the electron backscatter diffraction (EBSD) data, it was revealed that, though all 12 kinds of α variants appeared under different cooling rates, the area percentage of some variants remarkably deviated from the corresponding theoretical values at different cooling rates. To characterize the change of variant selection quantitatively, the length fraction of α/α boundary distinguished by types of angle/axis was further analyzed statistically. The results show that the length fraction of α/α boundary of type IV (63.26°/[?10 5 5 –3]) is larger than that of other types when the cooling rate is high (bottom zone) due to the high residual stress, while at low cooling rates (middle zone), the α/α boundary of type II (60°/[11–20]) dominates, which could be attributed to the self-accommodation mechanism during the β → α phase transition. The insights gained about the influence of cooling rate on the selection of α variant are helpful for understanding the microstructural evolution in LSFed Ti alloys.
查看更多>>摘要：? 2022Plastic flow machining (PFM) is a novel severe plastic deformation (SPD) process. Ultrafine-grained metal sheets or strips with gradient structures are processed by PFM in a single step under the combined effects of cutting and pressing. In this paper, the formation mechanism, mechanical properties, and thermal stability of pure copper sheets with gradient structures for different extrusion thicknesses were studied. The results implied that there was a pronounced gradient in terms of strain, grain size, and hardness across the sheet thickness. As the extrusion thickness was varied from 1.0 to 1.6 mm, the increasing thickness of the deformed coarse-grained layer contributed to decreases in the yield strength (YS) and ultimate tensile strength (UTS) and an increase in the elongation after fracture. As a result, the distribution of the gradient structure across the sheet thickness was controllable. There were considerable improvements in hardness, YS, and UTS and only a small reduction in elongation after fracture. In addition, after annealing at 150 °C, the hardness and tensile properties of the sheets were slightly different than those of the untreated sheets, indicating that the sheets had good thermal stability below this annealing temperature. Thus, PFM is an efficient SPD process for preparing the gradient structure sheets with high strength and reasonable ductility.
查看更多>>摘要：? 2022 Elsevier Inc.In this paper, based on the effect of different intermetallic compounds on liquid metal induced embrittlement (LMIE) and corrosion resistance of GI coating during hot-forming process, a low-aluminum, low-magnesium Zn-Al-Mg alloy with high corrosion resistance is designed by CALPHAD method. The equilibrium phase diagram and solidification path of Zn-Al-Mg(-Sn) zinc-rich corner are calculated, and the phase composition of the alloy is predicted and verified by experiments. The results show that the calculation results based on the CALPHAD method are highly reliable and can provide guidance for material design. The Mg-Zn phase in the melted Zn-Al-Mg alloy is Mg2Zn11, which is different from the MgZn2 phase in the traditional industrial field. This difference may be attributed to the difference of alloy element content and cooling rate. After the Sn is added on the basis of Zn-Al-Mg, hcp-Zn phase is initially precipitated in the alloy, then fcc-Al and Mg2Zn11 phases are precipitated at the same time, and then hcp-Zn + fcc-Al + Mg2Zn11 + Mg2Sn phase coexists. Finally, the phase is transformed into hcp-Zn + fcc-Al + Mg2Sn ternary eutectic. In addition, the corrosion resistance of the designed alloy shows that the Mg2Zn11 phase in eutectic structure can improve the corrosion resistance, while the improvement of the corrosion resistance of Mg2Sn is weaker than the Mg2Zn11 phase.
查看更多>>摘要：? 2022 Elsevier Inc.The coherent edge interface structures of the relatively thin {111}Al Ω plates have been analyzed in a peak-aged Al-Cu-Mg-Ag alloy by atomic-resolution scanning transmission electron microscopy (STEM). Analysis of STEM images showed that these edge interfaces can deviate from their orthogonal orientations to the broad plate surfaces. The edge interface tilts correlate with orientations of the shear components appearing along the broad plate surfaces and changing with the plate thicknesses. Cu atoms tend to occupy specific atomic sites in the Al matrix region close to the edge interfaces.
查看更多>>摘要：? 2022 Elsevier Inc.Partially biodegradable Ti–Mg composites were prepared by microwave sintering using the elemental Ti and Mg powders. The effect of Mg contents on the microstructure, mechanical properties, corrosion resistance, Mg degradation behavior of the Ti–Mg composites was investigated. The number of block Mg distributed over the Ti matrix gradually increases with increasing the Mg contents, in which the Mg and Ti form the metal-metal composite, and the interface of Mg and Ti is well bonded. The compressive strength of the Ti–Mg composites gradually decreases from 625 MPa to 357 MPa with increasing the Mg contents, while the elastic modulus varies little, ranged from 4.8 GPa to 5.7 GPa. The corrosion resistance of the Ti–Mg composites in SBF solution gradually decreases with increasing the Mg contents, resulting in the increase of hydrogen evolution amount. According to the electrochemical impedance spectroscopy, the corrosion and degradation of the Ti–Mg composites in SBF solution can be divided into three stages: the corrosion and degradation of Mg, the formation of Mg(OH)2 layer and the dissolve of Mg(OH)2 layer coupled with the formation of hydroxyapatite layer.
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