查看更多>>摘要：? 2022 Elsevier B.V.Enhancing service temperature of commercial MCrAlY series coatings to above 1100 °C becomes a new challenge. The aluminization seems be a possible solution. In this work, different Al contents aluminized NiCrAlYSi coatings were prepared. The microstructure, elemental distribution and cyclic oxidation performance of aluminized NiCrAlYSi coating with different Al contents have been investigated, using a substrate of Mo-rich single-crystal nickel-based superalloy. The Al content dependence of coating-air oxidation resistance and coating-substrate diffusion behavior is obtained at 1200 °C. These results demonstrate that this gradient aluminization is a cost-effective way to resolve service temperature enhancement. This also establishes a trade-off that adding Al content increases formation of dense Al2O3 scales with the sacrifice of surface smoothness.
查看更多>>摘要：? 2022 Elsevier B.V.Copper-chromium-zirconium (CuCrZr) is tailored using additive manufacturing, particularly laser powder bed fusion (LPBF). Due to high thermal conductivities and high reflectivity of infrared laser irradiation, it is still challenging to fabricate copper alloys using the LPBF technique. To address the issue, a short wavelength laser (515 nm) was employed in the LPBF process. In this work, the CuCrZr alloys were built with optimized building parameters such as powder of 485 W, scanning speed of 400 mm/s, and hatching distance of 0.09 mm. The relative density of the samples was found to be 98.07 %. The as-built samples exhibit good mechanical properties with ultimate tensile strength (UTS) of 447 ± 13 MPa, yield strength (YS) of 400 ± 11 MPa, total failure elongation (EL) of 10 ± 3 %, and Vickers hardness of 130 ± 15 HV). However, the electrical property is poor with 30 ± 1 %IACS. The high tensile stress and low electrical conductivity may attribute to the dislocation cells. Moreover, the dissolved Cr atoms result in poor conductivity. By direct aging treatment at 500 °C for 1 h, excellent mechanical properties (UTS = 566 ± 18 MPa, YS = 487 ± 13 MPa, EL = 15 ± 1 %, Vickers hardness = 161 ± 15 HV) were achieved while maintaining a good conductivity (64 ± 3 % IACS). The main contribution to the increase in YS is attributed to (I) the nanoscale Cr precipitated homogeneously in the copper matrix during the direct aging treatment and (II) the remaining high dislocation density near the dislocation cells. The enhancement of the electrical conductivity is attributed to the decomposition of the supersaturated solid solution.
查看更多>>摘要：? 2022 Elsevier B.V.On the example of the PbTe compound we present the results of the study of the interplay between the crystallographic orientation of the surfaces of high reticular density and easy cleaving of the crystals of cubic symmetry and the shape of surface structures induced by prolonged ion sputtering. We found that in case of right combination of the crystallographic orientation of both the sputtering surface and the planes of high reticular density in the aggregate with easy cleaving of the crystals, the pyramidal structures of pseudo-hexagonal shape can be formed on the sputtering surface of cubic crystals. In case of PbTe these are the surfaces of (111) crystallographic orientation subject to the presence of sputter-resistant protective shields on them. When the protective shields are destroyed, the hexagonal structures are transformed into trihedral pyramids. The pseudo-hexagonal pyramidal structures are characterized by indistinct edges and terrace-shaped lateral facets, whereas the facets of the trihedral pyramids, into which they are transformed during the ion bombardment, are mirror-smooth. We prove that: (a) the maximally sharpened pseudo-hexagonal pyramids, ion-induced on PbTe (111) sputtering surfaces, are formed as a result of self-organization of the crystallographic planes of the family {0ī2}, the reticular density of which directly follows the reticular density of the plane of the sputtered surface; (b) the roughness of the lateral facets of pseudo-hexagonal pyramids, as well as the mirroring of the facets of the trihedral pyramids is due to the impact of crystallographic planes of the {100}family, which are the planes of the greatest reticular density and easiest cleaving for PbTe crystals.
查看更多>>摘要：? 2022 Elsevier B.V.A “green” and simple approach was used to prepare a composite of strontium titanate and graphite-like carbon nitride (an STO/g-CN composite) that protected 304 stainless steel (304 SS) via photoelectrochemical cathodic protection (PCP). The structural characterization and optical-absorption characterization of the composite showed that g-CN was successfully loaded onto STO. The optical absorption spectrum of the composite showed an obvious redshift, and the optical response range of the composite extended to 540 nm. In addition, the composite showed enhanced PCP performance. Coupling 304 SS with the STO/g-CN composite containing 30 wt% of g-CN shifted the potential of the 304 SS from ?180 mV to ?480 mV. Moreover, the STO/g-CN composite containing 30 wt% of g-CN generated 3.8 times more photocurrent density than STO did. After 4 intermittent-light cycles, the STO/g-CN composite retained its PCP performance. The flower-like structure on the STO surface had many voids that provided a large surface area and many reaction sites and improved the ability of the composite to refract and utilize visible light. In addition, STO and g-CN formed a heterojunction whose charge-transfer mechanism inhibited photogenerated electrons and holes from recombining and improved the PCP performance of the STO/g-CN composite.
查看更多>>摘要：? 2022 Elsevier B.V.A new method is proposed to predict the formation of high-entropy single-phase oxide with a pyrochlore structure synthesis from non-equivalent principal elements. Based on this concepte, the La2B2O7 (B = Zn2+, Mg2+/Ni2+, Ce4+/Zr4+/Hf4+/Sn4+/Ti4+, W6+, Mo6+) were designed, in which high-entropy La2(ZnMgZrWMo)2O7, La2(ZnMgHfWMo)2O7 and La2(ZnMgSnWMo)2O7 pyrochlore ceramics were successfully prepared by solid-phase sintering. The microstructure of the entropy-stabilized phase was demonstrated using X-ray diffraction and elemental mapping, and the thermal properties including the thermal expansion coefficient and thermal conductivity were analyzed. The results show that La2(ZnMgZrWMo)2O7 has a higher thermal expansion coefficient (13.9 × 10–6 K–1) and lower thermal conductivity (0.8 W/m·K) than its corresponding single-components compound. In addition, La2B2O7 (B = Zn2+, Mg2+, Zr4+/Hf4+/Sn4+, W6+, Mo6+) pyrochlore high-entropy ceramics exhibit good calcium – magnesium – aluminosilicate (CMAS) resistance, the apatite protective layer generated after the reaction of La with CMAS effectively prevents further corrosion. This study suggests a novel method for predicting the formation of high-entropy single-phase oxides of pyrochlore structures and provides a new design concept for anti-CMAS corrosion materials.
查看更多>>摘要：? 2022 Elsevier B.V.Micro-stress distribution interior of TC21 alloy under abrasive processing was systematically investigated by combining EBSD data and crystal plasticity finite element model (CPFEM). The ductility enhanced of ground specimens after aging treatment, which can be attributed to the randomness of crystal orientation increased result in the decrease of micro-stress in polycrystal. For prismatic slip {101ˉ0}〈12ˉ10〉, the α-colonies with SF value of 0.16 suggest that further slip activation becomes difficult, leading to a higher local stress concentrated on grain boundaries of α-lamellae. The higher micro-stress almost distributed at the interface of α-lamellae with a preferred orientation, while in randomly oriented grains, higher micro-stress distributed interior of some grains or local interface of α-lamellae. Moreover, the maximum micro-stress in randomly oriented grains is smaller than that of preferred orientation grains.
查看更多>>摘要：? 2022 Elsevier B.V.The field of tailoring the physio-chemical properties by the way of radiation leads to the immense opportunities in the domain of advanced photonics and optoelectronic devices. In the present contribution, 120 MeV silver ions (Ag9+) induce electronic excitations which instigate modifications in crystalline cadmium sulphide (CdS) thin films deposited via electron beam evaporation are examined. X-ray Diffraction (XRD) reveals that the peak intensity and FWHM get affected as a consequence of swift heavy ions (SHI) irradiation while crystal phase remains preserved even after irradiation. Raman analysis exhibits the asymmetry in the fundamental longitudinal optical (LO) phonon mode which is directly related to the surface defects, reduction in particle size, and amorphization after irradiation. Field emission scanning electron microscopy (FESEM) images exhibit the reduction in particle size followed by highly strained as-deposited samples get stabilize with the deposited energy. The spherical shaped nanoparticles are observed for as-deposited and irradiated films through atomic force microscopy (AFM) and also, declared the nano-grain formation as resulted from negative surface tension induced at higher fluences. Photoluminescence (PL) spectra indicate the electronic excitations inspired additional yellow band due to generation of ICd-Vcd Frenkel pair defects along with the green and red emission.
查看更多>>摘要：? 2022 Elsevier B.V.The Mg-Sn-Y alloys exhibiting advanced elevated-temperature strength up to 300 ℃ were newly developed by tailoring precipitates through partially substituting and increasing yttrium (Y) (2, 3.5 wt%) for tin (Sn) in Mg-2.5Sn alloy. The effects of precipitates on the room/elevated-temperature mechanical properties, and the related dynamic precipitation behavior were investigated. The elevated-temperature strengthening mechanism of the alloy was revealed. The precipitates transformed from Mg2Sn in Mg-Sn alloy to Sn3Y5 in Mg-Sn-Y alloys. The abundant Sn3Y5 nanoparticles formed in the as-extruded Mg-0.5Sn-3.5Y alloy which exhibited significant higher peak strength as 223 MPa compared to that of Mg-2.5Sn as 53 MPa. The calculation of the critical nucleation energy for dynamic precipitation indicated that the Mg-Sn-Y alloys exhibited a smaller nucleation barrier for dynamic precipitation of dense nanoscale Sn3Y5 particles compared to the Mg-Sn alloy. This barrier was further decreased with increasing Y content, as exemplified by the increased area fraction of nanoparticles in the Mg-0.5Sn-3.5Y alloy. The abundant Sn3Y5 nanoparticles can inhibit the grain boundary crack propagation, and the formed fine grains (~3.8 μm) can effectively hinder the dislocation motion. Therefore, the present work demonstrated that coupling a high area fraction of thermally stable nanoparticles with grain refinement can provide an effective approach to acquire superior elevated-temperature strength for Mg alloys.
查看更多>>摘要：? 2022 Elsevier B.V.Exploring efficient photocatalysts to facilitate water splitting into green hydrogen (H2) energy is of great significance nowadays. In this work, we successfully synthesized CdS nanoflowers coated by zero-dimensional MMoS4 (M = Ni, Co, Cu) cocatalysts using a mild two-pot solvothermal method. Notably, 2.5%-NiMoS4/CdS catalyst exhibits optimal photocatalytic H2 evolution from benzyl alcohol aqueous solution under visible-light irradiation, and its photocatalytic H2 activity (7269.5 μmol·h?1·g?1) is 10.1 times higher than that of pure CdS (716.6 μmol·h?1·g?1). Simultaneously, benzyl alcohol can be synergistically converted into benzaldehyde after dehydrogenation. Such excellent photocatalytic performance mainly benefits from the existence of an internal electric field (IEF), which is demonstrated by experimental analysis and density functional theory calculations. And the IEF greatly accelerates the separation of electron-hole pairs during the photocatalytic H2 evolution process.
查看更多>>摘要：? 2022 Elsevier B.V.MXenes, a family of the typical two-dimensional materials, that are considered to be an excellent candidate material for supercapacitors, due to their large surface area, high conductivity and high specific pseudocapacitance. However, when assembled into electrode, MXene nanosheets are easy to aggregate because of the strong Van der Waals force. The assembled dense structure will limit the transport of electrolyte, decrease the active sites and electrochemical performance. In this work, in order to suppress the self-restacking of nanosheets and introduce more electrolyte transport channels, Ti3C2Tx nanosheets are partially oxidized and etched to get porous nanosheets. Film electrode based on porous Ti3C2Tx nanosheets shows higher specific surface area (48.3 m2/g) and improved electrochemical performance, including a high specific capacitance of 385 F/g at 1 A/g and good cycle stability of 92 % after 10,000 CV cycles at 100 mV/s.
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