查看更多>>摘要：? 2022 Elsevier B.V.The effect of substituting FeCo in Ni site maintaining their same ratio on structural, magnetocaloric, and magneto-transport properties of all-d-metal Ni50-x(FeCo)xMn37Ti13 (x = 16, 18, and 20) Heusler alloys are investigated. These alloys undergo a first-order magnetostructural transition (MST) between low temperature weak magnetic martensite (monoclinic or orthorhombic structure) to a high temperature ferromagnetic (FM) austenite (cubic structure) phase around room temperature. The MST temperature is observed to shift towards the lower temperature with increasing (FeCo)x content. These alloys with x = 16, 18, and 20 exhibit isothermal magnetic entropy change (?SM) as large as about ~13.8, ~12.7 and ~11.8 JkgK?1 across their MST associated with an effective refrigerant capacity (RCeff) of about 119.9, ~126.2 and ~194.4 J/kg respectively due to an application of 5 T magnetic field. It is interesting to note that ?SM remains almost identical over a large temperature region with (FeCo)x content from 16 to 20 at%. In addition, the maximum values of large magnetoresistance (MR)~ ?26.1% for x = 16, ?25.4% for x = 18, and ?24.3% for x = 20 are achieved at the field of 5 T. These materials with large magnetocaloric response in an extended temperature window around room temperature as well as large negative MR can be considered as potential candidates for multifunctional application.
查看更多>>摘要：? 2022 Elsevier B.V.The work describes the role of Nb addition on the magneto-structural properties of magnetron sputtered Si/SiO2/W/(CoFeB)1?xNbx (x = 0, 3, 5 and 10) metal metalloid alloy thin films. Films were grown at substrate temperature (Ts) of RT, 300 °C and 500 °C to realise the influence of Nb content in the amorphous and nano-crystalline states of (CoFeB)1?xNbx thin films. RT deposited films are soft magnetic (coercivity (Hc) ≤ 10 Oe), exhibits amorphous microstructure and display a well-defined uniaxial magnetic anisotropy (UMA) in the film plane. At 300 °C, devitrification occurs, and the film (x = 0) becomes partially crystalline with precipitation of FeCo nano-crystals, and UMA nearly disappears. With increasing Nb content, the mean grain size and amount of FeCo nano-crystals decreases, and partially crystalline CoFeB films transform to a completely amorphous microstructure with the simultaneous appearance of in-plane UMA and systematic improvement in soft-magnetic nature (Hc decreases from~22–5 Oe). Nb addition on at Ts= 500 °C results in grain growth inhibition and magnetically isotropic (CoFeB)1?xNbx films (except x = 3). The present study demonstrates that thermally stable amorphous CoFeB films with desired soft magnetic properties can be prepared by appropriate selection of Nb content and suitable growth temperature.
查看更多>>摘要：? 2022 Elsevier B.V.The effects of isothermal temperature and duration on the microstructures and anisotropic mechanical properties of bimodal 6A02 Al semi-solid billets were studied. These semi-solid billets were fabricated by semi-solid isothermal treatment of hot extruded aluminum alloy (SSITHEAA) method. Elongated and equiaxed grains owning different dislocation densities coexisted at 610–650 °C for 5–30 min. With the increase of temperature, the intensities of micro-textures and intragranular dislocation decreased. The average Schmid factors in transverse directions were still larger than those along extruding directions, preliminarily predicting anisotropic features from the perspective of grain orientation. The anisotropic features of bimodal semi-solid microstructures were verified firstly by uniaxial tensile tests in 0°, 45°, and 90° directions, among which 0 ° specimen at 610 °C/ 20 min exhibited the highest tensile strength and ductility (yield strength σy of 103.8 MPa, maximum tensile strength σmax of 286.9 MPa, and elongation δ of 22.0%). Different from microstructures at solid temperatures, recrystallization degraded mechanical strength of semisolid microstructures to some degree once the grain boundaries were soaked with liquid phase. The dislocation strengthening inside the deformed grains and solid solution strengthening were two dominant strengthening mechanisms. Besides, the elongated grains improved the mechanical properties through dislocation pileup inside the grains, “bridging” effect, “necking” effect and decreasing the content of both flaws and liquid phase. The in-plane anisotropy (IPA) factor indicated that the elongation bore the most serious anisotropy. On the whole, the isotropy of 650 °C/20 min billet was the best, and the corresponding IPA values of σy, σmax and δ were 21.9%, 26.2%, and 47.0%, respectively. For 0° specimens, ductile fracture was dominant, but brittle characteristic was increasingly significant for 45° and 90° specimens.
查看更多>>摘要：? 2022 Elsevier B.V.In this study, the high temperature uniaxial tensile creep deformation behavior of (α + β)-Mg-9 mass%Li-4 mass%Al-1 mass%Zn (LAZ941) alloy was investigated. The creep strength of the LAZ941 alloy was significantly improved by heat treatment. The creep deformation behavior of the heat-treated LAZ941 alloy was unique. As the results of creep tests, it is found that the stress exponent of LAZ941 was about 3. The activation energies of creep at the early and middle stages of deformation were 114.7 and 84.6 kJ?mol?1, respectively, indicating that the diffusing elements controlling the viscous glide of the dislocation changed during creep deformation.
查看更多>>摘要：? 2022 Elsevier B.V.Al2-xScxMo3O12 (x = 0 ? 0.6) ceramics were utilised using a convenient solid-state reaction. The doped Sc3+ took the place of Al3+ and formed a pure Al2-xScxMo3O12 phase. With the doping of Sc3+, the phase transition temperature was adjusted from 178 °C to below room temperature when x ≥ 0.4. Besides, the Q × f increased a lot. Pure monoclinic Al2Mo3O12 presented microwave dielectric properties of εr = 6.76, Q × f = 27,330 GHz and τf = ?59.52 ppm/°C and changed from monoclinic phase to orthorhombic phase at 178 °C. When x = 0.4, Al1.6Sc0.4Mo3O12 presented orthorhombic phase at room temperature. Pure orthorhombic Al1.5Sc0.5Mo3O12 showed the best microwave dielectric properties of εr = 7.26, Q × f = 82,000 GHz and τf = ?53.91 ppm/°C.
查看更多>>摘要：? 2022 Elsevier B.V.Two-dimensional graphene nanoplates (GNPs) with a high aspect ratio and outstanding mechanical properties is an excellent reinforcement for fabricating aluminum-based composites. The laser powder bed fusion (L-PBF) technique has been employed for fabricating GNPs/aluminum composites. Unfortunately, the GNPs/aluminum composites prepared by L-PBF exhibit limited enhancement in strength and ductility due to the increased graphene defects and the formation of Al4C3 carbides. In this study, we added ZrO2 nanoparticles to the GNPs/AlSi10Mg composite to further improve its strength and ductility. The GNPs/ZrO2/AlSi10Mg composite samples were fabricated by L-PBF. Compared with the L-PBF prepared GNPs/AlSi10Mg and ZrO2/AlSi10Mg composite samples, the as-built GNPs/ZrO2/AlSi10Mg composite sample exhibits the highest tensile strength of 537.9 ± 10 MPa and ductility of 11.2 ± 1%. This result indicates that GNPs/ZrO2 provide dual enhancements in tensile strength and ductility for the L-PBF prepared GNPs/ZrO2/AlSi10Mg composite sample. The GNPs/ZrO2 nanofiller-induced enhancements in strength and ductility were discussed in depth in this study.
查看更多>>摘要：? 2022 Elsevier B.V.A new multi-principal Al-Co-Ni-Cu alloy with high damping and good corrosion resistance was prepared. The effects of the Al content on the microstructure, damping properties, corrosion behavior, and mechanical properties of AlxCoNi2Cu (x = 0, 0.1, 0.3, and 0.5) alloys were studied. AlxCoNi2Cu (x = 0–0.5) alloys exhibited face-centered cubic (FCC) crystal structures. The Al0.5CoNi2Cu alloy displayed a significant increase in the internal friction (IF) value (Q?1) compared to other AlxCoNi2Cu alloys (x = 0–0.3). The maximum Q?1 of the Al0.5CoNi2Cu alloy was 0.032, which was twice that of AlxCoNi2Cu (x = 0–0.3) alloys and almost equal to that of the traditional Mn-Cu damping alloy. The mechanism for the sudden increase in the damping property of the alloys was explained by the interaction between the precipitated Ni3Al phase and the dislocations generated during the nucleation process. Moreover, the Al0.5CoNi2Cu alloy exhibited a lower corrosion current and rate in electrochemical and immersion tests in a 3.5 wt% NaCl solution compared to AlxCoNi2Cu (x = 0–0.3) alloys. Supersaturated Al solubilized in the matrix, resulting in the formation of Al2O3 protective films which effectively delayed the corrosion process. In addition, the Al0.5CoNi2Cu alloy exhibited good corrosion resistance, comparable to that of ferritic stainless steel, making it a promising candidate for marine applications.
查看更多>>摘要：? 2022 Elsevier B.V.Tin-based materials, which are one of the materials that store Li-ion through an alloying reaction, have been actively studied as anode materials for Li-ion and Na-ion batteries thanks to their high capacity, high electrical conductivity, and low cost. In this paper, we propose a porous Sn2Nb2O7-graphene oxide (GO) composite material that is prepared by a two-step hydrothermal and pyrolysis process. The ternary Sn2Nb2O7 material decomposes into Sn and niobium oxide during the first Li or Na insertion reactions and the niobium oxide acts as a buffer medium to alleviate the volume changes of Sn, as well as a Li/Na storage material through intercalation. Furthermore, a porous structure combined with GO was introduced into the composite, which increased the cycling stability of the electrode. The synthesized material was characterized by X-ray diffraction (XRD), electron microscopy, and X-ray photoelectron spectroscopy. The electrochemical reaction mechanism with Li was thoroughly investigated by ex situ XRD analysis. The electrochemical test results demonstrated that the composite electrode has great potential as both Li-ion and Na-ion anodes because of its high reversible capacity and initial Coulombic efficiency, as well as enhanced cycling and rate performance. The electrochemical performance can be attributed to the incorporation of a porous structure and GO.
查看更多>>摘要：? 2022 Elsevier B.V.High-performance Cu-Cr-Zr-X alloys are regarded as novel structural materials for nuclear fusion reactors. Through combining the experiments and density functional theory (DFT), the effect of Si addition on precipitation behavior and related properties of Cu-Cr-Zr-(Si) alloy was investigated for higher performance. Compared with the Si-free alloy, precipitation of Cr-rich phase is accelerated in the Cu-Cr-Zr-Si alloy (aging time<30 min at 450 °C). The partial radial distribution functions of the Cu-rich matrix reveal that the formation of Si-Cr clusters is resulted from the attractive Si-Cr binding energies at the nearest-neighbor distance. Moreover, the addition of Si can reduce the Cr migration energy in Cu. At the initial stage of aging at 550 °C, the precipitation kinetics is dominated by temperature. By TEM analysis, it is indicated that the growth of Cr-rich phase in Cu-Cr-Zr-Si alloy is delayed, which may be attributed to the decrease of Cu/Cr interface energy due to the addition of Si, as confirmed by first-principles calculations. The optimized performance of aged Cu-Cr-Zr-Si alloy can be achieved at 450 °C/4 h, and Orowan strengthening is dominant. This work can provide a guideline for design of novel high-performance Cu-Cr-Zr-X alloys.
查看更多>>摘要：? 2022 Elsevier B.V.Sintered neodymium iron boron (NdFeB) has been widely applied in various industrial fields thanks to its excellent magnetic properties. However, the impact loads in increasing number of applications challenged its mechanical safety and magnetic field reliability. This is a blind spot in the existing researches on the properties of sintered NdFeB. To tackle this, this article proposes a dynamic damage constitutive model and impact demagnetization model respectively to illustrate the dynamic mechanics and impact demagnetization process of sintered NdFeB. Specifically, Split Hopkinson Pressure Bar (SHPB) experiments are conducted to obtain the dynamic response of sintered NdFeB at different strain rates. The dynamic fracture process of NdFeB is also analyzed by combining the damage constitutive model based on experimental data with the SHPB dynamic simulation model. This is the foundation of the demagnetization model in subsequent. Different from the previous researches on complete demagnetization caused by intensive impacts at the magnitude of GPa, the demagnetization study in this article is aimed at the more regular impacts below 100 MPa. Based on the stress knee hypothesis and irreversible aggravation hypothesis respectively, the reversible and irreversible processes during the demagnetization are individually demonstrated in the form of magnetic domain flip. The specific comparison between simulation and experimental results verified the effectiveness of the demagnetization model.
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