查看更多>>摘要：? 2022 Elsevier B.V.Additively manufactured (AM) eutectic Al alloy systems have been studied extensively for advantageous thermal stability and mechanical properties due to their refined microstructures. Al-Cu-Ce alloys are one subset of these AM eutectic alloys. Here we studied phase stability in AM Al-Cu-Ce alloys and compared it to that of conventionally cast ones. A new phase, Al8Cu3Ce, was identified in the microstructures of both AM and cast Al-Cu-Ce alloys. This Al8Cu3Ce phase was not previously included on experimental or thermodynamically calculated phase diagrams of the Al-Cu-Ce system. Therefore, we performed additional thermodynamic modeling of the system. These models were experimentally validated with cast and subsequently heat-treated Al-Cu-Ce alloys. We found that despite the refined microstructure of the AM alloys, the phases formed were consistent with the cast alloys, suggesting that AM processing did not significantly alter the formation and stability of phases from that in the conventional alloys. This work has resolved inconsistent previous descriptions of the Al-Cu-Ce ternary phase diagram in the Al-rich region and resulted in the addition of the Al8Cu3Ce as an equilibrium phase above 500 ℃.
查看更多>>摘要：? 2022 Elsevier B.V.The efficacy of peening treatment depends on the plasticity of the target metal. In this study, the effectiveness of high-amplitude short duration pulsed current in improving the peening efficacy was examined in a process called electropulsing-assisted ultrasonic nanocrystal surface modification (EP-UNSM). During the EP-UNSM process, the target metal, i.e., Ti64, is subjected to simultaneous ultrasonic peening and electropulsing. The high energy pulsed current can generate a critical magnetic field that can induce the transition of the radical pairs formed by dislocations and the pinning obstacles from the singlet state to the triplet state. This leads to higher dislocation mobility and thus higher plasticity for more effective peening treatment. The results show that the sample treated with EP-UNSM had a deeper plastically deformed layer than that for samples subjected to UNSM and continuous current–assisted UNSM (CC-UNSM), and the maximum depth of plastic deformation was obtained when using the highest peak current density. Due to microstructure refinement, work hardening, and dynamic strain aging, the EP-UNSM sample had a 50% higher surface hardness compared with the control sample. Moreover, the compressive residual stresses generated by EP-UNSM were higher in magnitude and greater in depth compared to those generated by traditional UNSM. These results demonstrate that pulsed current can effectively improve the peening efficacy and EP-UNSM is an effective method for strengthening Ti64.
查看更多>>摘要：? 2022Nanostructured materials with unique structural properties have attracted the interest of researchers, because these materials are rich in active sites, offer enhanced ion transport, and are robust for application in electrochemical energy storage and conversion. However, the synthesis of nanocubes of morphological metal phosphides, especially secondary metal-supported metal phosphide nanostructures, is still under research, due to the generation of synergistic effects. In this article, we present a Mn–Co metal phosphide in a nitrogen-doped carbon matrix (MnCoP4 @NC), using zeolite imidazolate framework-67 (ZIF-67) nanocubes. The addition of the surfactant cetyltrimethylammonium bromide (CTAB) changes the morphology of dodecahedra to nanocubes during synthesis at room temperature. The ZIFs are then phosphided in a tube furnace at 450 °C in a nitrogen gas atmosphere. In addition, the electrochemical performance of the synthesized materials was investigated using the hydrogen evolution reaction (HER). The MnCoP4 @NC shows excellent electrocatalytic activity of 206 mV overpotential to reach 10 mA·cm?2 current density, as well as very good kinetic behavior and long-term stability up to a 25 h chronopotential run. The proposed material synthesis will support the development of nanoarchitecture materials for electrocatalyst-based energy applications.
查看更多>>摘要：? 2022 Elsevier B.V.In electrochemical alcohol oxidation reactions catalysed by supported Pt-based nanoparticles, the catalytic performance is highly correlated with the electron density accumulated over the metal's surface. The highly electronegative nature of Pt, affects the catalytic performance by accumulating electrons generated over the oxidative reaction on the Pt surface. It was found that alloying Cu to Pt enhances greatly the catalyst's activity and robustness. This enhancement is due to the redox reaction of Cuδ+ species into Cu0 with the electrons generated during the reaction. Here, we show that an oxidative pretreatment of the carbon support XC-72R with HNO3 or H2O2 can further boost the catalysis of alcohol oxidation. This is mainly explained by the effect of enriched O-containing functional groups introduced in the support materials, which stabilize the presence of Cuδ+ species in the bimetallic Pt-Cu nanoparticles. This process increases the hydrophilic wettability, which enables more adsorption of reactant molecules and hydroxide ions over the catalyst's surface, as demonstrated by DFT calculations. The proposed catalytic system is applicable to a variety of substrates, including methanol, ethanol, isopropanol and sorbitol. Our work emphasizes the importance of support's modification in tuning the interaction within the bimetallic nanoparticles and thus enhancing the electrocatalytic oxidation reactions’ activity.
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