查看更多>>摘要：Profound and comprehensive investigations on the morphology characteristics of α precipitates are essential for the microstructural control of metastable β titanium alloys.At the very beginning of aging treatment,intragranular α precipitates with a dot-like morphology begin to generate nearby the dislo-cations,then those dot-like α precipitates with the same crystallographic orientation tend to connect with each other to develop a lath-like morphology.With the progress of aging treatment,the orientated lath-like α precipitates gradually combine with each other to form the V-shaped clusters or the triangular ones.The dislocations of{1(-1)0}β < 11 (-1)>β edge type are evidenced within the β grains,and it is found that variant selection ofα precipitates induced by the transformation strain and the interplay between α vari-ants and the dislocations are confirmed as the key factors for the formation of the V-shaped or triangular clusters.The results of this work could provide underlying knowledge on the morphology characteristics of intraguranular α precipitates related to the crystal defects and the strain accommodation of α variants in metastable β titanium alloys.
查看更多>>摘要：Degradation of a metallic film under harsh thermal-mechanical-electrical coupling field conditions deter-mines its service temperature and lifetime.In this work,the self-heating degradation behaviors of Pt thin films above 1000 ℃ were studied in situ by TEM at the nanoscale.The Pt films degraded mainly through void nucleation and growth on the Pt-SiNx interface.Voids preferentially formed at the grain boundary and triple junction intersections with the interface.At temperatures above 1040 ℃,the voids nucleated at both the grain boundaries and inside the Pt grains.A stress simulation of the suspended membrane suggests the existence of local tensile stress in the Pt film,which promotes the nucleation of voids at the Pt-SiNx interface.The grain-boundary-dominated mass transportation renders the voids grow preferen-tially at GBs and triple junctions in a Pt film.Additionally,under the influence of an applied current,the voids that nucleated inside Pt grains grew to a large size and accelerated the degradation of the Pt film.
查看更多>>摘要：This research studied the mechanisms of Ca and Zn microalloying on the enhancement of ductility of extruded Mg-Gd sheet by combing electron backscattered diffraction and slip trace analysis.The ductil-ity and microstructure of extruded Mg-0,6Gd and Mg-0.6Gd-0.3Ca-0,2Zn (wt％) sheets were investigated.Basal slip was the main deformation mode under investigation.Ca and Zn microalloying increased the frequency of grain boundaries (GBs) with misorientation angles (θs) ＜ 35°,promoted slip transfer across GBs and restricted the basal slip localization.In addition,there were a higher number of GB cracks homo-geneously distributed in the Mg-0.6Gd sheet than in the Mg-0.6Gd-0.3Ca-0.2Zn sheet,attributed to the increased cohesion of GBs.The enhancement of basal slip,the suppression of slip localization and the suppression of GB cracking were contributed to the increased ductility for Mg-0.6Gd-0.3Ca-0.2Zn sheet.
Yuanyuan QiaoXiaoying LiuNing ZhaoLawrence C M Wu...
29-39页
查看更多>>摘要：The morphology and orientation evolution of Cu6Sn5 grains formed on (001)Cu and (011)Cu single crystal substrates under temperature gradient (TG) were investigated.The initial orientated prism-type Cu6Sn5 grains transformed to non-orintated scallop-type after isothermal reflow.However,the Cu6Sn5 grains with strong texture were revealed on cold end single crystal Cu substrates by imposing TG.The Cu6Sn5 grains on (001)Cu grew along their c-axis parallel to the substrate and finally merged into one grain to form a fully IMC joint,while those on (011)Cu presented a strong texture and merged into a few dominant Cu6Sn5 grains showing about 30° angle with the substrate.The merging between neighboring Cu6Sn5 grain pair was attributed to the rapid grain growth and grain boundary migration.Accordingly,a model was put forward to describe the merging process.The different morphology and orientation evolutions of the Cu6Sn5 grains on single crystal and polycrystal Cu substrates were revealed based on crystallographic relationship and Cu flux.The method for controlling the morphology and orientation of Cu6Sns grains is really benefitial to solve the reliability problems caused by anisotropy in 3D packaging.
查看更多>>摘要：Laser powder bed fusion (L-PBF) of Sc/Zr-modified Al-based alloys has recently become a promising method for developing a new generation of high-performance Al alloys.To clarify the modification roles of Sc/Zr elements,an Al-4.66Mg-0.48Mn-0.72Sc-0.33Zr (wt.％) alloy was processed using L-PBF.The ef-fect of the local solidification condition of the molten pool on the precipitation behavior of primary Al3(Sc,Zr) was analyzed based on time-dependent nucleation theory.it was found that primary Al3(Sc,Zr)inevitably precipitated at the fusion boundary,while its precipitation could be effectively suppressed in the inner region of the molten pool.This subsequently induced the formation of a heterogeneous α-Al matrix.After direct aging,the heredity of solidification microstructure introduced heterogeneous secondary Al3(Sc,Zr) precipitates within α-Al matrix.Owing to the inverse relationship between grain boundary strengthening and precipitation strengthening,the direct-aged sample with dual heterogeneous structures exhibited reduced mechanical heterogeneity,resulting in lowered hetero-deformation-induced hardening.The low strain-hardening capability in the direct-aged sample promoted necking instability while inducing a large Lüders elongation,which effectively improved the tensile ductility.
查看更多>>摘要：Diatomite supported nano zero valent iron (nZVI) catalyst (NDA) with complex network structure was prepared via a mild reduction precipitation method in this work.The pore structure and pore distribu-tion of NDA can be regulated and controlled through adjusting the loading amount of nZVI.In general,the nano three-dimensional network formed by nZVI and diatomite channels greatly increase the specific surface area and pore volume of NDA,and further formed more active sites,which made NDA have better performance in activating PMS to degrade BPA than pure nZVI.The pseudo-first-order reaction rate con-stant of 50-NDA (50％-nZVI/diatomite) is almost 3 times higher than that of pure nZVI.Besides,the elec-tron paramagnetic resonance (EPR) and radical quenching experiments showed that the activation process was dominated by the sulfate radical (SO4·-) and hydroxyl radical (OH) produced by Fe0 oxidation.The generated electrons promote the self-decomposition of PMS to produce singlet oxygen (1O2),and then the valence state of iron changes to produce free radicals.In addition,the possible degradation pathway of BPA was inferred from the intermediate products identified by liquid chromatograph-mass spectrom-eter (LC-MS).This study provides a novel strategy for the design and preparation of three-dimensional composite catalysts derived from natural mineral.
查看更多>>摘要：Hydrogen evolution reaction (HER) through water splitting is a promising way to solve the energy short-age.Noble-metal-free HER electrocatalysts with high efficiency is very important for practical applica-tions.Herein,we prepare the Ni3S4@MoS2 electrocatalyst on carbon cloth (CC) through a two-step hy-drothermal process.The Ni3S4 nanorods are uniformly integrated with the MoS2 nanosheets,forming a hierarchical structure and heterogeneous interfaces.The fast electron transfer on the interface en-hances the kinetics of catalytic reaction.The hierarchical structure provides more exposed active sites.The Ni3S4@MoS2/CC exhibits good catalytic activity and long-term stability for HER.This work provided a practicable strategy to develop efficient electrocatalysts for HER in alkaline media.
查看更多>>摘要：Carbon fibers going through stabilization,carbonization,and graphitization heat-treatment stages will form continuous graphitic layers that are closely packed and preferentially aligned along the fiber axis,forming high mechanical stiffness or strength and electrical or thermal conductivity.The alignment of noncontinuous,powder-like graphene layers in polymers has been challenging due to the low bend-ing modulus of a few-or even single-layered graphene,which causes aggregations or folding behav-iors.This research demonstrates the leveraging of polymer-nanoparticle interactions to align graphene nanoplatelets (GNPs) in the polyacrylonitrile (PAN) matrix.An in-house designed spinning method pro-duces a three-layered fiber that utilizes the interracial interactions between each layer for graphene align-ment between graphitic layers.This composite containing oriented GNPs significantly improves modulus(i.e.,42.3 to 74.6 GPa) and increases electrical conductivity for enhancing volatile organic compounds(VOCs) sensing behaviors.This research opens up a new scalable fabrication method for multilayered composites.
查看更多>>摘要：The high-strength Al-Zn-Mg-Cu alloy provides much better dent resistance and weight-reduction poten-tial compared to the conventional Al alloys used for the automobile body panels.However,natural age-ing (NA) significantly reduces the formability of Al-Zn-Mg-Cu alloy.The reversion of natural ageing has been systematically investigated by hardness test,tensile test,differential scanning calorimetry (DSC) and transmission electron microscopy (TEM).Substantial reversion of natural ageing and thus hardness de-crease occurs immediately upon thermal treatment at 120-210 ℃ in an Al-Zn-Mg-Cu alloy.Although the hardness of the most reverted state decreases with increasing temperature,the lowest hardness is still higher than the as-quenched state by 30HV.As revealed by the complementary DSC and TEM observa-tions,this is ascribed to the synchronization of the dissolution and the re-precipitation of the solutes in the NA clusters during reversion ageing.Reversion at 180-210 ℃ for less than 30 s leads to a hardness decline of 40HV.The hardening kinetics during NA after reversion is slower than that during first-time NA due to the reduced vacancy concentration.Artificial ageing at 180 ℃ for 30 min after secondary NA of less than 24 h induces intensive precipitation of plate-like pre-ηphases and a giant strength increase of 188-204 MPa.Potential use of high strength Al-Zn-Mg-Cu alloy in automobile body panels could be realized by appropriate reversion treatment improving the formability and the quick bake hardening re-sponse.
查看更多>>摘要：In this article,graphene oxide (GO) and benzotriazole-loaded mesoporous silica nanoparticles (BTA/MSNs)are combined on micro scale through the in situ polymerization of polydopamine (PDA),preparing a self-healing bi-functional GO (fGO) used as nano-fillers for anti-corrosion enhancement of waterborne epoxy(WEP) coatings.Scanning electronic microscopy (SEM) images show that the BTA/MSNs are uniformly distributed on the surface of high aspect ratio GO nanosheets to endow GO nanocontainer characteristics.UV-vis profiles demonstrate that fGO has pH-controlled release function.Modulus at lowest frequency is generally used for comparing the corrosion resistance of organic coatings.Modulus at lowest frequency(1.42 × 107 Ω cm2) after 30 days immersion in 3.5 wt.％ NaCl solution revealed 2 orders of magnitude higher that of blank WEP (1.17 × 105 Ω cm2).With artificial cracks on its coatings,fGO/WEP had no obvious rust compared with blank WEP after 240 h of immersion.We anticipate that self-healing and physical barrier bi-functional nanocontainers improve the traditional anticorrosion coating efficiency with better,longer-lasting performance for shipping,oil drilling or bridge maintenance.
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