Dual-Material Electron Beam Selective Melting:Hardware Development and Validation Studies

Electron beam selective melting （EBSM） is an additive manufacturing technique that directly fabricates three-dimensional parts in a layerwise fashion by using an electron beam to scan and melt metal powder. In recent years, EBSM has been successfully used in the additive manufacturing of a variety of materials. Previous research focused on the EBSM process of a single material. In this study, a novel EBSM process capable of building a gradient structure with dual metal materials was developed, and a powder-supplying method based on vibration was put forward. Two different powders can be supplied individually and then mixed. Two materials were used in this study： Ti6AI4V powder and Ti47AI2Cr2Nb powder. Ti6AI4V has excellent strength and plasticity at room temperature, while Ti47AI2Cr2Nb has excellent performance at high temperature, but is very brittle. A Ti6AI4V/Ti47AI2Cr2Nb gradient material was successfully fabricated by the developed system. The microstructures and chemical compositions were characterized by optical microscopy, scanning microscopy, and electron microprobe analysis. Results showed that the interface thickness was about 300 μm. The interface was free of cracks, and the chemical compositions exhibited a staircase-like change within the interface.

Unusual Charge Transport and Spin Response of Doped Bilayer Triangular Antiferromagnets

Within the t-J model, the charge transport and spin response of the doped bilayer triangular antiferromagnetare studied by considering the bilayer interaction. Although the bilayer interaction leads to the band splitting in theelectronic structure, the qualitative behaviors of the physical properties are the same as in the single layer case. Theconductivity spectrum shows the low-energy peak and unusual midinfrared band, the temperature-dependent resistivityis characterized by the nonlinearity metallic-like behavior in the higher temperature range and the deviation from themetallic-like behavior in the lower temperature range and the commensurate neutron scattering peak near the half-fillingis split into six incommensurate peaks in the underdoped regime, with the incommensurability increasing with the holeconcentration at lower dopings, and saturating at higher dopings.

IrNi nanoparticle-decorated flower-shaped NiCo_2O_4 nanostructures:controllable synthesis and enhanced electrochemical activity for oxygen evolution reaction

In this work,we demonstrated the enhanced oxygen evolution reaction（OER） activity of flower-shaped cobalt-nickel oxide（NiCo_2O_4） decorated with iridium-nickel bimetal as an electrode material.The samples were prepared by carefully depositing pre-synthesized IrNi nanopartides on the surfaces of the NiCo_2O_4 nano-flowers.Compared with bare NiCo_2O_4,IrNi,and IrNi/Co_3O_4,the IrNi/NiCo_2O_4 exhibited significantly enhanced electrocatalytic activity in the OER,including a lower overpotential of 210 mV and a higher current density at an overpotential of 540 mV.We found that the IrNi/NiCo_2O_4 showed more efficient electron transport behavior and reduced polarization because of its bimetal IrNi modification by analyzing its Tafel slope and turnover frequency.Furthermore,the electrocatalytic mechanism of IrNi/NiCo_2O_4 in the OER was studied,and it was found that the combined active sites of the composite effectively improved the rate determining step.The synergic effect of the bimetal and metal oxide plays an important role in this reaction,enhancing the transmission efficiency of electrons and providing more active sites for the OER.The results reveal that IrNi/NiCo_2O_4 is an excellent electrocatalyst for OER.

Dual-metal precursors for the universal growth of non-layered 2D transition metal chalcogenides with ordered cation vacancies

Two-dimensional(2D)transition metal chalcogenides(TMCs)are promising for nanoelectronics and energy applications.Among them,the emerging non-layered TMCs are unique due to their unsaturated dangling bonds on the surface and strong intralayer and interlayer bonding.However,the synthesis of non-layered 2D TMCs is challenging and this has made it difficult to study their structures and properties at thin thickness limit.Here,we develop a universal dual-metal precursors method to grow non-layered TMCs in which a mixture of a metal and its chloride serves as the metal source.Taking hexagonal Fe_(1-x)S as an example,the thickness of the Fe_(1-x)S flakes is down to 3 nm with a lateral size of over 100 μm.Importantly,we find ordered cation Fe vacancies in Fe_(1-x)S,which is distinct from layered TMCs like MoS_(2) where anion vacancies are commonly observed.Low-temperature transport measurements and theoretical calculations show that 2D Fe_(1-x)S is a stable semiconductor with a narrow bandgap of60 meV.In addition to Fe_(1-x)S,the method is universal in growing various non-layered 2D TMCs containing ordered cation vacancies,including Fe_(1-x)Se,Co_(1-x)S,Cr_(1-x)S,and V_(1-x)S.This work paves the way to grow and exploit properties of non-layered materials at 2D thickness limit.

In-situ electropolymerized bipolar organic cathode for stable and high-rate lithium-ion batteries

To address the dissolution issue and enhance the electrochemical performance of organic electrode materials,herein, a bipolar organic cathode was prepared by in-situ electropolymerization of amino-phenyl carbazole naphthalene diimide(APCNDI). APCNDI is composed of n-type 1,4,5,8-naphthalene tetracarboxylic diimide that stores Li cations and p-type carbazole groups which react with anions and serve as polymerization sites. Electropolymerization completely eliminated the dissolution problem of APCNDI, and the electropolymerized cathode demonstrated a bipolar reaction with excellent electrochemical performance, stable cycling performance with a capacity retention of 92 mA h g;after1000 cycles, and a superior rate performance of 72 mA h g;at 10 A g;. The bipolar feature and reactions of APCNDI were systematically investigated and verified by multiple characterization techniques. Our findings provide a novel strategy for the design and fabrication of electrodes for high-performance organic batteries.