High-Entropy Alloys and Their Affinity with Hydrogen: From Cantor to Platinum Group Elements Alloys.

Properties of high-entropy alloys are currently in the spotlight due to their promising applications. One of the least investigated aspects is the affinity of these alloys to hydrogen, its diffusion, and reactions. In this study, high pressure is applied at ambient temperature and stress-induced diffusion of hydrogen is investigated into the structure of high-entropy alloys (HEA) including the famous Cantor alloy as well as less known, but nevertheless important platinum group (PGM) alloys. By applying X-ray diffraction to samples loaded into diamond anvil cells, a comparative investigation of transition element incorporating HEA alloys in Ne and H2 pressure-transmitting media is performed at ambient temperature. Even under stresses far exceeding conventional industrial processes, both Cantor and PGM alloys show exceptional resistance to hydride formation, on par with widely used industrial grade Cu-Be alloys. The observations inspire optimism for practical HEA applications in hydrogen-relevant industry and technology (e.g., coatings, etc), particularly those related to transport and storage.

Synergistically Improved Thermoelectric Energy Harvesting of Edge-Oxidized-Graphene-Bridged N-Type Bismuth Telluride Thick Films.

Power generation through the thermoelectric (TE) effect in small-sized devices requires a submillimeter-thick film that is beneficial to effectively maintain ΔT compared with a micron-scale thin film. However, most TE thick films, which are fabricated using printing technologies, suffer from low electrical conductivity due to the porous structures formed after sintering of the organic binder-mixed TE ink. In this study, we report an n-type TE thick film fabricated through bar-coating of the edge-oxidized-graphene (EOG)-dispersed Bi2.0Te2.7Se0.3 (BTS) paste with copper dopants. We have found that EOG provides the conducting pathway for carriers through electrical bridging between the separated BTS grains in porous TE thick films. The simultaneous enhancement in electrical conductivity and the Seebeck coefficient of the EOG-bridged TE film result in a maximum power factor of 1.54 mW·m-1·K-2 with the addition of 0.01 wt % EOG. Furthermore, the single element made of an n-type EOG-bridged BTS exhibits a superior output power of 1.65 µW at ΔT = 80 K. These values are 5 times higher than those of bare BTS films. Our results clearly indicate that the utilization of EOG with a metal dopant exerts a synergistic effect for enhancing the electrical output performance of n-type TE thick films for thermal energy harvesters.

Synergetic enhancement in the reactivity and stability of surface-oxide-free fine Al particles covered with a polytetrafluoroethylene nanolayer.

Surface oxide (Al2O3) of reactive fine aluminum (Al) particles for solid fuels, propellants, and brazing materials often restricted oxidative performance, though the passivation film acts to protect Al particles from exploding. Here, we report fine Al particles fully covered with a polytetrafluoroethylene (PTFE) layer instead of an Al2O3 film on the surface. This advance is based on the introduction of strong Al-F bonds, known to be an alternative to the Al-O bonds of surface oxides. The DSC results on the PTFE-coated Al particles exhibit higher reactive-exothermic enthalpy energy (12.26 kJ g-1) than 4.85 kJ g-1 by uncoated Al particles. The artificial aging test of the PTFE layer on the Al particles show long-time stability to the external circumstance compared to those by Al2O3. The activation energy for oxidation was investigated from cyclic voltammetry assessment and the measured peak potentials of the anode curve for PTFE/Al (- 0.45 V) and uncoated Al (- 0.39 V) are achieved, respectively. This means that the PTFE layer is more stable against a sudden explosion of Al particles compared to Al2O3. These results are very useful given its capability to control both the reactivity and stability levels during the oxidation of Al particles for practical applications.

Correlation Between Microstructure and Tensile Properties of STS 316L and Inconel 718 Fabricated by Selective Laser Melting (SLM).

The correlation between microstructure and tensile properties of selective laser melting (SLM) processed STS 316L and Inconel 718 were investigated at various heights (top, middle and bottom) and planes (YZ, ZX and XY). Columnar grains and dendrites were formed by directional growth during solidification. The average melt pool width and depth, and scan track width were similar in both specimens due to fixed processing parameters. SLM Inconel 718 has moderate tensile strength (1165 MPa) and tensile elongation (11.5%), whereas SLM STS 316L has outstanding tensile strength (656 MPa) and tensile elongation (75%) compared to other SLM processed STS 316L. Fine columnar diameter (0.5 µm) and dense microstructures (porosity: 0.35%) in SLM STS 316L promoted the enhancement of tensile elongation by suitable processing condition. Fractographic analysis suggested that the lack of fusion pore with unmelted powder should be avoided to increase tensile properties by controlling processing parameters.

Fluoroscopic images-based aiming and targeting system with two line lasers for insertion guidance of interlocking screw.

PURPOSE: Minimally invasive surgery is widely used for managing fractures; however, it is difficult to determine the exact screwing position of intramedullary nails inserted into bone. To address this problem, we developed the aiming and targeting system by laser (ATLAS) using two line lasers to mark the position of the surgical tool directly on the skin. METHODS: ATLAS consists of a laser module, controller, personal computer, and display device. The laser module is fixed to the intensifier side of the C-arm. Calibration with dedicated markers is required prior to using the system. After calibration, the laser modules can mark the selected point on a fluoroscopic image acquired with the C-arm as the intersection of the two line lasers on the skin. RESULTS: To verify the effectiveness of ATLAS, marking accuracy was measured. The average control error of the device itself was 0.57 mm. In the experimental setting using C-arm fluoroscopy, the accuracy was within 1.5 mm at 23 of the 25 measurement points and within 3 mm at the remaining two points. CONCLUSION: ATLAS shows the corresponding points in real space with respect to fluoroscopic images using cross-points of lasers. The proposed method is clinically useful to aid the insertion of interlocking screws in minimally invasive surgeries for bone fractures. We believe that ATLAS enables more accurate marking through C-arm fluoroscopy and is more convenient, and it can thus be applied in various orthopedic surgeries.

Micro-Texture Analyses of a Cold-Work Tool Steel for Additive Manufacturing.

Small objects of an alloy tool steel were built by selective laser melting at different scan speeds, and their microstructures were analyzed using electron backscatter diffraction (EBSD). To present an explicit correlation with the local thermal cycles in the objects, prior austenite grains were reconstructed using the EBSD mapping data. Extensive growth of austenitic grains after solidification could be detected by the disagreement between the networks of carbides and austenite grain boundaries. A rapid laser scan at 2000 mm/s led to less growth, but retained a larger amount of austenite than a slow one at 50 mm/s. The rapid scan also exhibited definite evolution of Goss-type textures in austenite, which could be attributed to the growth of austenitic grains under a steep temperature gradient. The local variations in the microstructures and the textures enabled us to speculate the locally different thermal cycles determined by the different process conditions, that is, scan speeds.

In-Situ Deposition of Graphene Oxide Catalyst for Efficient Photoelectrochemical Hydrogen Evolution Reaction Using Atmospheric Plasma.

The vacuum deposition method requires high energy and temperature. Hydrophobic reduced graphene oxide (rGO) can be obtained by plasma-enhanced chemical vapor deposition under atmospheric pressure, which shows the hydrophobic surface property. Further, to compare the effect of hydrophobic and the hydrophilic nature of catalysts in the photoelectrochemical cell (PEC), the prepared rGO was additionally treated with plasma that attaches oxygen functional groups effectively to obtain hydrophilic graphene oxide (GO). The hydrogen evolution reaction (HER) electrocatalytic activity of the hydrophobic rGO and hydrophilic GO deposited on the p-type Si wafer was analyzed. Herein, we have proposed a facile way to directly deposit the surface property engineered GO.

Thermo-mechanical improvement of Inconel 718 using ex situ boron nitride-reinforced composites processed by laser powder bed fusion.

Hexagonal boron nitride-reinforced Inconel 718 (h-BN/IN718) composites were fabricated using a laser powder bed fusion (LPBF) technique to treat a nanosheet-micropowder precursor mixture prepared in a mechanical blending process. Tailoring the BN in IN718 enhanced the thermal resistance of the composites, thereby dampening the sharpness of the melting temperature peak at 1364 °C. This is because the presence of the BN reinforcement, which has a low coefficient of thermal expansion (CTE), resulted in a heat-blocking effect within the matrix. Following this lead, we found that the BN (2.29 g/cm3) was uniformly distributed and strongly embedded in the IN718 (8.12 g/cm3), with the lowest alloy density value (7.03 g/cm3) being obtained after the addition of 12 vol% BN. Consequently, its specific hardness and compressive strength rose to 41.7 Hv0.5 ·cm3/g and 92.4 MPa·cm3/g, respectively, compared to the unreinforced IN718 alloy with 38.7 Hv0.5 ·cm3/g and 89.4 MPa·cm3/g, respectively. Most importantly, we discovered that the wear resistance of the composite improved compared to the unreinforced IN718, indicated by a decrease in the coefficient of friction (COF) from 0.43 to 0.31 at 2400 s. This is because the BN has an exfoliated surface and intrinsically high sliding and lubricating characteristics.

Preparation of conductive Cu thin film by the reaction of Cu nitrate with polymers.

Cu nanoparticle-colloid was prepared by using electrical wire explosion process in liquid and it showed good dispersion stability without any kinds of additives. Mixed Cu nano-colloid was prepared with Cu nanoparticle-colloid, Copper (II) nitrate trihydrate, and polyvinyl pyrrolidone. Cu atoms are supplied from the dissociation reaction between Copper (II) nitrate trihydrate and polyvinyl pyrrolidone and fill up the gaps between Cu nanoparticles during the thermal sintering. Conductive (45 microOmega cm) Cu film was prepared at the sintering temperature of 200 degrees C by the enhancement of the formation of sintering necks.