查看更多>>摘要：? 2022Enhanced magnetostriction in FeGa-based alloys has been attributed to the tetragonal modified-D03 nanoinclusions. However, the dependence of the magnetostricitive properties on the size and volume fraction of the modified-D03 phase remains unclear. Here, the morphology evolution and density change of modified-D03 nanoinclusions in (Fe81Ga19)99.9Tb0.1 single crystal were characterized by transmission electron microscopy upon in-situ heating process (298 K to 773 K), and their correlative influence on magnetostriction behavior was revealed. The morphology and density of modified-D03 nanoinclusions vary slightly when heating temperature is lower than 473 K, leading to the almost unchanged magnetostriction in (Fe81Ga19)99.9Tb0.1 alloys. When heating from 473 K to 773 K, modified-D03 nanoinclusions evolve into a band-like distribution rather than being randomly distributed in A2 matrix at lower temperature, and the magnetostrictive properties decrease with the increased size of modified-D03 nanoinclusions from ~5 nm to ~25 nm during the heating process. The decreased density of modified-D03 nanoinclusions caused by phase transition from modified-D03 to A2 results in further reduction of magnetostrictive properties when heating at 773 K. The magnetostriction of (Fe81Ga19)99.9Tb0.1 single crystal can recover to 325 ppm by quenching from 973 K, which results from the re-precipitation of modified-D03 nanoinclusions with small size. The results provide a basis for optimizing the magnetostrictive performance of Fe81Ga19(Tb) alloys. The enhanced magnetostriction of Fe81Ga19(Tb) alloys could be obtained by quenching from temperature higher than 773 K.
查看更多>>摘要：? 2022 Elsevier Inc.The effect of cold-rolling and high-temperature aging on precipitation processes in an Al–Er–Zr alloy was investigated by microhardness and resistivity measurements, scanning electron microscopy, (scanning) transmission electron microscopy and X-ray diffraction. Many similarities with the Al–Sc–Zr system have been shown. Based on the obtained results, following decomposition sequence of supersaturated solid solution of the Al–Er–Zr-based alloy has been proposed: Er-rich clusters → Al3Er phase → layer rich in Zr (Al3(Er,Zr) phase). Cold-rolling enhances the precipitation of Al3Er particles and accelerates the process identified as formation of the Zr-rich shell around the Er-rich core of Al3(Er,Zr) precipitates. The effect of precipitation strengthening is negligible compared to the effect of work hardening as the supersaturation of Er in the Al matrix was probably considerably lowered by formation of Er-rich primary precipitates observed in the as-prepared state of the alloys studied. The core–shell structure of the Al3(Er,Zr) particles formed after 2 and 4 h of aging at 600 °C was confirmed by Z contrast imaging and X-ray energy dispersive spectroscopy. The coherency strain-field around the precipitates is retained even after 4 h of aging at 600 °C. The Er/Zr atomic ratio of the precipitates was estimated based on their lattice constant.
查看更多>>摘要：? 2022The porous 3D scaffolds with three types of pore structure A, B and C were created by the direct metal laser sintering (DMLS) technology from the powders of titanium Ti-6Al-4V alloy. Calcium phosphate (CPC) and Zn?calcium phosphate (Zn-CPC) coatings were formed on the 3D scaffolds by the micro-arc oxidation (MAO) method in the acidic electrolyte. As well as another calcium phosphate (CPL) and Ag?calcium phosphate (Ag-CPL) coatings, that were synthesized in the alkaline electrolyte. Preliminary studies of the surface morphology, elemental and phase composition, and strength properties of the coatings were carried out on the plate samples from titanium Ti-6Al-4V alloy using scanning electron microscopy (SEM), X-ray diffraction, and scratch testing. The surface morphology of the coatings on the 3D scaffolds was also investigated via SEM method. The internal pore structure of both the coated and uncoated samples was examined by the Micro-CT analysis. It was found that the coatings were evenly distributed over the surface and in the inner pore structure of the all types of the 3D scaffolds. The biological studies carried out on both the plate samples and the 3D samples have shown that the coatings demonstrated no cytotoxic effect on cell culture of human fibroblast pFb. All the coatings, excluding CPL, exhibited high antibacterial activity against bacteria MRSA ATCC 43300 and Escherichia coli ATCC 25922.
查看更多>>摘要：? 2022 Elsevier Inc.Conductive atomic force microscopy was used to image permalloy nanostructures embedded in Al2O3. Two layers of permalloy nanostructures embedded in Al2O3 were fabricated in a stacked manner using nanosphere lithography and electron beam evaporation. Bias dependence conduction of the bottom and top layers of the permalloy nanostructures was demonstrated. A simple phenomenological model based on thermionic emission, direct tunnelling and Fowler-Nordheim tunnelling was used to explain the experimental findings. When applied to Co-HfO2 granular films, the technique enabled 3D reconstructed images of the films to obtain grain size information in a non-destructive manner. This relatively simple and cost-effective technique has the potential to be developed to image nanostructures and devices tomographically.
查看更多>>摘要：? 2022Understanding the relationships between composition, structure, processing and properties helps in the development of improved materials for known applications as well as for new applications. Materials scientists, chemists and physicists have researched these relationships for many years, until the recent past, by characterizing the bulk properties of functional materials and describing them with theoretical models. Magnets are widly used in electric vehicles (EV), hybrid electric vehicles (HEV), data storage, power generation and transmission, sensors etc. The search for novel magnetic phases requires an efficient quantitative microstructure analysis of microstructural information like phases, grain distribution and micromagnetic structural information like domain patterns, and correlating the information with intrinsic magnetic parameters of magnet samples. The information out of micromagnetic domains helps in obtaining the optimized microstructures in magnets that have good intrinsic magnetic properties. This paper is aimed at introducing the use of a traditional machine learning (ML) model with a higher dimensional feature set and a deep learning (DL) model to classify various regions in sintered NdFeB magnets based on Kerr-microscopy images. The obtained results are compared against reference data, which is generated manually by subject experts. Additionally, the results were compared against the approach for grain analysis, which is based on the electron backscatter diffraction (EBSD) technique. Further, the challenges faced by the traditional machine learning model for classifying microstructures in Kerr micrographs are discussed.
查看更多>>摘要：? 2022In this work, full Cu3Sn joints were aged at 500°C, 550°C, and 600°C for various durations. Microstructure evolution and grain morphology of the joints were systematically investigated by OM, SEM, EBSD, and TEM technology. In addition, the mechanical properties of hardness and shear strength for the Cu–Sn intermetallic compounds were studied using a Micro Vickers hardness tester and uniaxial tensile equipment. Upon heating to 500°C, the phase transformation pathway was Cu3Sn–Cu41Sn11–α(Cu); aging at 550°C demonstrated a pathway of Cu3Sn–Cu41Sn11–Cu41Sn11&α(Cu)–α(Cu); and finally, heating to 600°C resulted in a phase transformation pathway of Cu3Sn–Cu20Sn6–Cu20Sn6&α(Cu)–α(Cu). It was found that longer aging times and higher temperatures had effects on grain size and morphology. For the 500°C group, the average grain size of the fully formed Cu41Sn11 phase increased from 1.93 μm at an aging time of 20 min to 4.20 μm at 30 min. The grain sizes of the fully formed Cu41Sn11 phase in joints subjected to 550°C for 11 min was lower than 2.36 μm, which were in turn smaller than joints treated at 500°C for 30 min (4.2 μm). Treatment with higher temperatures resulted in more cores and a higher growth rate of Cu41Sn11 grains formed on the interface of Cu/Cu3Sn, which eventually led to the small grain size of the Cu41Sn11 phase. The grain morphologies of the formed Cu41Sn11 phase and Cu20Sn6 phase were mainly column grain. After an aging time of 11 min for the 550°C group, the grain morphology of α(Cu) included in a two-phase microstructure (Cu41Sn11&α(Cu)) mainly exhibited dendritic properties at the grain boundary of Cu41Sn11, its crack tendency broke the hardenability of single grains for the Cu41Sn11 phase, which resulted in a decline in strength from 107 MPa to 42 MPa for Cu41Sn11&α(Cu) compared to the Cu41Sn11 phase. Nevertheless, for the joints treated at 600°C after an aging time of 7 min, the dispersion of α(Cu) particles mainly followed granular shapes within the one large Cu20Sn6 grain in the two-phase microstructure (Cu20Sn6&α(Cu)). This blocked the extension of dislocation, which finally led to an enhancement in strength for the Cu20Sn6 & α(Cu) phase (51 MPa) compared to the Cu20Sn6 phase (73 MPa).
查看更多>>摘要：? 2022 Elsevier Inc.The deformation mechanism and microstructure evolution of the extruded Mg[sbnd]2Nd alloy were investigated in the hot tensile deformation process at strain rate of 2.2 × 10?4 s?1 and deformation temperatures of 150 °C–300 °C. the results showed that the peak stress declines and the elongation to fracture increases with the increasing of deformation temperature. By observation of the microstructure, the fibrous extrusion zones (FEZs) and non-fibrous extrusion zones (non-FEZs) coexist in the alloy, and the microstructure deformation of the FEZs is more obvious than that of the non-FEZs. In the initial deformation stage, the grain deformation first occurs in the FEZs. In the later deformation stage, recrystallization occurs in both FEZs and non-FEZs. Moreover, the deformation mechanism of the FEZs is different from that of the non-FEZs. The deformation mechanism of the FEZs is dominated by intragranular slip, supplemented by grain boundary slip (GBS). The recrystallization mechanism in FEZs is continuous dynamic recrystallization (CDRX). On the contrary, the deformation of the non-FEZs is dominated by GBS, while the intragranular slip plays a coordinated role. The recrystallization mechanism in non-FEZs is discontinuous dynamic recrystallization (DDRX). Therefore, the dominated hot tensile deformation mechanisms of the alloys are alternated among intragranular slip, GBS and dynamic recrystallization (DRX)
查看更多>>摘要：? 2022γ'-strengthened Co-based superalloy is bonded by a Transient liquid phase bonding process using the Ni-Cr-W-B filler alloy, and the solidification behavior of the joint is studied by using in-situ microstructure characterization and computer simulation. Results indicate the isothermal solidification layer is composed of γ'/γ phase, and the solid/liquid interface is prone to grow with cellular morphology due to the large compositional undercooling zone caused by the rapid diffusion of B. The athermally solidified zone is composed of the γ phase, M3B2, MB, and M23B6. The solidification sequence is that: γ + M3B2 eutectic, γ + MB eutectic, and the γ + CrB + M23B6 ternary eutectic. The formation of the M23B6 instead of the theoretically predicted Ni3B in the ternary eutectic is mainly because the Al, Cr, Co, and Ta elements do not diffuse sufficiently and are left in the residual liquid. These elements make the formation energy of the M23B6 lower than that of the M3B. Our experimental results help to understand the microstructural characteristics better and serve as a guide for further optimizing the microstructure of the TLP joint.
查看更多>>摘要：? 2022The effect of 2 wt% Ru on γ/γ' microstructural evolutions and precipitation of TCP phases were investigated in two experimental alloys. The two alloys were subjected to unstressed thermal exposure at temperatures of 1100 °C for periods of 100, 500 and 1000 h. The microstructures of the samples before and after thermal exposures were characterized. Directional coarsening of γ' phases and the precipitation of TCP phases were observed in the both alloys after long-term exposure. The experimental results show that Ru has a very significant effect on the suppression of TCP phases by influences the partitioning of elements. Detailed analysis showed that Ru increases the lattice misfit strain, resulting in more dense and stable interfacial dislocation networks, which can promote the stability of γ/γ' microstructures by delaying topological inversion. Ledges and grooves at γ/γ' interfaces associated with the dislocations and strong segregations of Cr, Co and Re along the dislocation networks were both observed, under which a detailed explanation of the coarsening process during thermal exposure was given.
查看更多>>摘要：? 2022 Elsevier Inc.Vast amounts of strengthening methods towards the single phase face-centered cubic CrCoNi medium-entropy alloy have been carried out in recent years. In this study, a partially recrystallized structure, as well as the fully recrystallized heterogeneous structure, were introduced in CrCoNi medium-entropy alloy through cold-rolling and subsequent annealing that purposely deployed under gradient temperatures. The annealed specimens were subjected to tensile tests, from which detailed parameters of the mechanical properties were derived. Strengthening from grain boundaries, dislocations, solid solutions are quantified, suggesting the existence of other strengthening mechanisms. We attribute the increased strength to the appearance of extensive shear bands, nanograins, nanotwins, HCP lamellas. In addition, the dual-heterogenous structure is believed to contribute to similar ultimate tensile strengths among the annealed specimens. More importantly, dislocations, stacking faults, twins appeared in this alloy as the deformation modes, contribute to the extraordinary fracture elongation.
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