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Additive manufacturing of in-situ strengthened dual-phase AlCoCuFeNi high-entropy alloy by selective electron beam melting
No full textThe application scope and market demand for additive-manufactured high-entropy alloys (AM HEAs) have broadened of late. However, a long-standing problem associated with AM HEAs is their limited ductility. In this study, a dual-phase AlCoCuFeNi HEA, consisting of body-centered cubic (BCC) solid solution matrix with uniformly dispersed face-centered cubic (FCC) structured precipitates, was fabricated by selective electron beam melting (SEBM). SEBM involved a preheating process can enable the formation of Cu-rich FCC phases with needle-like and spherical morphologies, as well as nanotwins that in-situ precipitated from the metastable BCC(B2) matrix. The compressive strength and ductility of the SEBM HEA were superior to those of the HEAs processed by selective laser melting (SLM) AM technique. Furthermore, using selective electron beam remelting (SEB-RM) during SEBM could result in a higher relative density, finer microstructure, and enhanced compressive properties. Particularly, the SEB-RM sample exhibited a better compressive strength of 2572 MPa, a yield strength of 870 MPa, and a strain of 18.3%. The improved mechanical properties of SEBRM samples could be ascribed to the refined grains and the formation of FCC precipitates, mostly along the grain boundaries. This provides new insights into the dual-phase HEAs-fabricated via a combination of the SEBM additive manufacturing process and selective electron beam remelting-that exhibit in-situ strengthening. (c) 2021 Elsevier B.V. All rights reserved
Mesoporous Ti0.5Cr0.5N for trace H2S detection with excellent long-term stability
No full textEfficient, accurate and reliable detection and monitoring of H2S is of significance in a wide range of areas: industrial production, medical diagnosis, environmental monitoring, and health screening. However the rapid corrosion of commercial platinum-on-carbon (Pt/C) sensing electrodes in the presence of H2S presents a fundamental challenge for fuel cell gas sensors. Herein we report a solution to the issue through the design of a sensing electrode, which is based on Pt supported on mesoporous titanium chromium nitrides (Pt/Ti0.5Cr0.5N). Its desirable characteristics are due to its high electrochemical stability and strong metal-support interactions. The Pt/Ti0.5Cr0.5N-based sensors exhibit a much smaller attenuation (1.3%) in response to H2S than Pt/C-sensor (40%), after 2 months sensing test. Furthermore, the Pt/Ti0.5Cr0.5N-based sensors exhibit negligible cross response to other interfering gases compared with hydrogen sulfide. Results of density functional theory calculation also verify the excellent long-term stability and selectivity of the gas sensor. Our work hence points to a new sensing electrode system that offers a combination of high performance and stability for fuel-cell gas sensors
Promoted formation of stereocomplex in enantiomeric poly(lactic acid)s induced by cellulose nanofibers
No full textStereocomplex (SC) crystallization between enantiomeric poly(L-lactic acid) (PLLA) and poly(D-lactic acid) (PDLA) is believed to yield poly(lactic acid) (PLA) with superior physiochemical properties. However, homocrystallization (HC) crystallites are inevitably generated in the PLLA/PDLA blends. Herein, we report a simple approach to fabricate PLLA/PDLA racemic blends with high contents of SC crystallites by introducing cellulose nanofibers (CNFs). The isothermal crystallization results revealed that the half-crystallization time of the PLLA/ PDLA blend was significantly decreased by adding CNFs. Additionally, with the incorporation of 3 wt% modified CNFs, the PLLA/PDLA blend was overwhelmingly crystallized into SC crystallites with no HC crystallite formation. Based on Fourier transform infrared spectroscopy findings, it was speculated that the preferred SC crystallization of PLLA/PDLA/CNF was caused by enhanced interchain molecular interactions between CNFs and PLA. This work presents a feasible and efficient method to fabricate PLA with exclusively SC crystallites, which possesses great potential for producing high-performance PLA materials
Experimental and numerical study on Mode I and Mode II interfacial fracture toughness of co-cured steel-CFRP hybrid composites
No full textInterfacial fracture toughness of co-cured steel-carbon fiber reinforced plastic (CFRP) hybrid composites were investigated in this paper. To illustrate the effect of the interlayer on the fracture toughness, steel-CFRP hybrid composites were prepared by different manufacturing processes based on steel surface treatment (abrasion or grit blasting) and adhesive-bonding process. The experimental results of double cantilever beam (DCB) tests and end notched flexure (ENF) tests demonstrate that, the Mode I and Mode II interfacial fracture toughness of the hybrid composites can be improved by using a grit blasting surface treatment on steel and introducing an adhesive layer at the steel/CFRP interface. The hybrid composites mainly show fiber/epoxy interfacial failure of CFRP under Mode I loading conditions, while it mostly exhibits adhesive failure of steel/CFRP interface under Mode II loading condition. Moreover, the interfacial tensile strengths of steel-CFRP hybrid composites are predicted by finite element analysis, and both experimental and numerical results confirm the improvement of interfacial fracture toughness
Mechanism of low thermal conductivity for Fe76Si13B8Nb2Cu1 amorphous and nanocrystalline alloys at room temperature
No full textFe-based amorphous and nanocrystalline alloys offer application prospects in the field of coating materials, and their thermal transport property is crucial for their application in thermal insulation coating. However, the mechanism of thermal conductivity in the process of isothermal annealing preparation of Fe-based nanocrystalline alloys are still unclear. In this work, the thermal conductivity of Fe76Si13B8Nb2Cu1 amorphous alloy isochronal annealed at different temperature was examined. It was found that the thermal conductivity of the amorphous alloy is as low as 7.06 W/mK, whereas significantly increases to 10.38 W/mK after annealing at 693 K for 1800s. The result of the limited increase in thermal conductivity at annealing temperatures below the 693 K can be ascribed to the conflicting variations of electronic and phonon contributions with increasing temperature. At annealing temperature above 693 K, the two contributors start to cooperate, leading to abrupt enhancement of thermal conductivity. This work provides an insight into the thermal transport mechanisms for amorphous alloys
Interfacial assembled mesoporous polydopamine nanoparticles reduced graphene oxide for high performance of waterborne epoxy-based anticorrosive coatings
No full textEmbedding two-dimension micro/nanocontainers containing corrosion inhibitors into organic coating is a well-established concept to impart the coating with enhanced barrier and self-healing feature. Herein, a versatile nanoemulsion assembly approach was used to synthesis nanocarriers combing mesoporous polydopamine nanoparticles (MPDA) with reduced graphene oxide (GO), which was employed to encapsulate corrosion inhibitors (benzotriazole, BTA) to improve the anticorrosion performance of waterborne epoxy coating. The BTA release profiles from synthesized GO with MPDA (PDAG) demonstrated the rapid pH-triggered activities to acidic corrosion environment. With the addition of BTA-loaded PDAG, the composited epoxy coatings presented self-repairing behavior and enhanced corrosion resistance during longterm immersion. The outstanding anticorrosion performance is attributed to dual-protection mechanism provided by BTA-loaded PDAG: (1) MPDA endows GO with satisfactory interface compatibilities and thus provides impermeable barrier to delay the penetration process of corrosive electrolyte; (2) corrosion inhibitors including BTA and polydopamine form the adsorption layers on bare steel surface to resist con-tinuous corrosion at metal/coating interface. (c) 2021 Elsevier Inc. All rights reserved
Processable poly(2-butylaniline)hexagonal boron nitride nanohybrids for synergetic anticorrosive reinforcement of epoxy coating (vol 131, pg 187, 2018)
No full textKinematics analysis and workspace optimization for a 4-DOF 3T1R parallel manipulator
No full textA four degrees-of-freedom (DOF) Parallel Manipulator (PM) with a 4PPa-2PaR configuration has been proposed to generate 3-DOF Translational and 1-DOF Rotational (3T1R) motions in our early work. It has the advantages of symmetric geometry, simple kinematics and infinite extension of translational workspace along its linear guide direction. However, its V-type assembly mode results in a long distance between its moving platform and the base, which makes its stiffness and accuracy lower. Besides, its the other two translational workspaces are limited due to its kinematic singularities. To overcome such limitations, the PM is modified by utilizing its M-type assembly mode and placing an offset angle to the last parallelogram mechanism. To simplify the displacement analysis, a geometrical projection method is employed, while a closed-loop vector approach is used for its instantaneous kinematic analysis. Both singularity and workspace issues are investigated. An optimization algorithm based on Genetic Algorithm is proposed to maximize the reachable workspace. The optimization result indicates that the workspace is significantly increased. A prototype of the M-type PM is fabricated to validate the effectiveness of the modified design
A change in the taxonomic rank of Senna andhrica P. V. Ramana, J. Swamy & M. Ahmed. (Fabaceae: Caesalpinioideae)
No full textUltrahigh-Volumetric-Energy-Density Lithium-Sulfur Batteries with Lean Electrolyte Enabled by Cobalt-Doped MoSe2/Ti3C2Tx MXene Bifunctional Catalyst
No full textIt is a significant challenge to design a dense high-sulfur-loaded cathode and meanwhile to acquire fast sulfur redox kinetics and suppress the heavy shuttling in the lean electrolyte, thus to acquire a high volumetric energy density without sacrificing gravimetric performance for realistic Li-S batteries (LSBs). Herein, we develop a cation-doping strategy to tailor the electronic structure and catalytic activity of MoSe2 that in situ hybridized with conductive Ti3C2Tx MXene, thus obtaining a Co-MoSe2/MXene bifunctional catalyst as a high-efficient sulfur host. Combining a smart design of the dense sulfur structure, the as-fabricated highly dense S/Co-MoSe2/MXene monolith cathode (density: 1.88 g cm(-3), conductivity: 230 S m(-1)) achieves a high reversible specific capacity of 1454 mAh g(-1) and an ultrahigh volumetric energy density of 3659 Wh L-1 at a routine electrolyte and a high areal capacity of similar to 8.0 mAh cm(-2) under an extremely lean electrolyte of 3.5 mu L mg s(-1) at 0.1 C. Experimental and DFT theoretical results uncover that introducing Co element into the MoSe2 plane can form a shorter Co-Se bond, impel the Mo 3d band to approach the Fermi level, and provide strong interactions between polysulfides and Co-MoSe2, thereby enhancing its intrinsic electronic conductivity and catalytic activity for fast redox kinetics and uniform Li2S nucleation in a dense high-sulfur-loaded cathode. This deep work provides a good strategy for constructing high-volumetric-energy-density, high-areal-capacity LSBs with lean electrolytes