The selective laser melting (SLM) of an equiatomic CoCrFeMnNi high-entropy alloy (HEA) powder was studied, with emphasis on its non-equilibrium microstructural evolution and mechanical properties. ...The printed sample density increases gradually with increasing laser energy density and then decreases at an over-high laser energy density. The microstructure of SLM printed HEA exhibits a large number dislocation pile-ups and lattice distortion. Of particular intrigue are the existence of nanotwins and tetragonal σ phase in SLM printed HEA; such nanotwins and σ phase have never been observed in either cast or deformed HEA with true strain below 3.7%. The grain refinement by rapid solidification and σ phase synergistically improve the mechanical properties, as compared with conventionally solidified HEA. Hot isostatic pressing (HIP) was performed to improve the densification, yielding the increase of tensile strength from 601 MPa of SLM printed sample to 649 MPa after HIP.
•The equiatomic CoCrFeMnNi alloy was successfully printed by SLM.•Solidifying stress yielded a large number of dislocation pile-ups.•Nanotwins were detected in SLM printed sample.•Tensile strength of SLM + HIP processed sample reaches 649 MPa.
Cost-effective electrocatalysts based on nonprecious metals for efficient water splitting are crucial for various technological applications represented by fuel cell. Here, 3d transition metal ...layered double hydroxides (LDHs) with varied contents of Ni and Fe were successfully synthesized through a homogeneous precipitation. The exfoliated Ni–Fe LDH nanosheets were heteroassembled with graphene oxide (GO) as well as reduced graphene oxide (rGO) into superlattice-like hybrids, in which two kinds of oppositely charged nanosheets are stacked face-to-face in alternating sequence. Heterostructured composites of Ni2/3Fe1/3 LDH nanosheets and GO (Ni2/3Fe1/3-GO) exhibited an excellent oxygen evolution reaction (OER) efficiency with a small overpotential of about 0.23 V and Tafel slope of 42 mV/decade. The activity was further improved via the combination of Ni2/3Fe1/3 LDH nanosheets with more conductive rGO (Ni2/3Fe1/3-rGO) to achieve an overpotential as low as 0.21 V and Tafel plot of 40 mV/decade. The catalytic activity was enhanced with an increased Fe content in the bimetallic Ni–Fe system. Moreover, the composite catalysts were found to be effective for hydrogen evolution reaction. An electrolyzer cell powered by a single AA battery of 1.5 V was demonstrated by using the bifunctional catalysts.
This study investigated the microstructure and anisotropic mechanical properties of selective laser melting (SLM) processed Inconel 718 (IN718) component. In as-fabricated alloys, ultrafine columnar ...grained microstructure with highly dispersed precipitates γ" phases at grains boundary and even-distributed γ' phases inside the grains were observed. It was demonstrated that the as-fabricated longitudinal samples showed lower ultimate tensile strength (UTS) of 1101MPa but higher elongation of 24.5% compared to the transverse samples which showed UTS of 1167MPa and elongation of 21.5%. The excellent mechanical properties of both the longitudinal and transverse samples can be ascribed to the refined microstructure of the SLM material resulting from the high cooling rate imposed by laser processing. The anisotropy in strength and ductility was attributed to the {100} fiber texture and columnar grain morphology. The {100} fiber texture of columnar grains leads to high strength in transverse direction, while the columnar grain boundaries also served as a path along which damage can preferentially accumulate, leading to fracture.
Display omitted
The atomic diffusion of a Fe–Al system under spark plasma sintering was investigated at temperatures ranging from 773 to 873K. A significant increase in the growth rate constant of ...Al13Fe4 and Al5Fe2 under the pulse current of spark plasma sintering was observed compared with the absence of current. The interdiffusion coefficient under pulse current was about 46 times higher than that without current at 873K. The activation energy for the interdiffusion was 332kJ/mol, which is higher than that without current of 155–190kJ/mol. Although the diffusion kinetics were enhanced, the thermodynamics state is not altered.
In this work, Cu-15Ni-8Sn components were manufactured by selective laser melting (SLM) with a near full density of about 99.4%. The microstructures and phase precipitation of the as-fabricated ...Cu-15Ni-8Sn alloy were characterized by X-ray diffraction (XRD), electron probe microanalyzer (EPMA), electron back-scattered diffraction (EBSD), and transmission electron microscope (TEM). It was demonstrated that the as-fabricated Cu-15Ni-8Sn alloy shows α-phase with γ-precipitates by XRD and TEM. The size of the grains of α-phase is in the range of 5~20 μm with random orientation distribution. The γ-precipitate is a Sn- and Ni-rich phase distributed dispersedly in matrix and accumulatively in grain boundary. The as-fabricated Cu-15Ni-8Sn alloy exhibited yield strength of 522 MPa, ultimate tensile strength of 653 MPa, and elongation of 17%. The excellent mechanical performance of the as-fabricated Cu-15Ni-8Sn alloy is caused by the local laser melting mode including rapid cooling rate and reduplicative fusing from the subsequent layer melting, which leads to refined grains and limited Sn segregation in micron-size within the matrix.
This study presents the microstructure and mechanical properties of an additive manufactured recyclable Al-2Fe alloy fabricated by laser powder bed fusion (LPBF). The microstructure evolution of the ...Al-2Fe alloy aged at elevated temperatures and its impact on the mechanical properties were systematically investigated. Firstly, the single melt scanning experiment verified that Al-Al6Fe anomalous eutectic structure was initially formed from the liquid phase. Secondly, the as-built Al-2Fe contains nano-size and rod-shaped Al6Fe particles which uniformly dispersed in a supersaturated Al matrix. The Al6Fe particles with an average diameter of ~89 nm shows a coherent crystallographic relationship with the matrix as (046)Al6Fe // (2¯02¯)Al, and 032¯Al6Fe // 1¯11Al. The ultimate tensile strength and total elongation of 287.0 MPa and 12.0% were obtained in the ultrafine as-built Al-2Fe, respectively. Aging at elevated temperatures made the Al6Fe particles coarsened and transformed into Al13Fe4 particles at 350 °C. The amount of the total Al-Fe intermetallic compounds (Al6Fe+Al13Fe4) increased with the aging temperature due to the precipitation of the supersaturated Fe atoms. It exhibits a slow increase in grain size and a decrease in dislocation density in the Al-2Fe samples with the increase of aging temperature. All Al6Fe particles were transformed into coarse Al13Fe4 particles at 550 °C. Thirdly, the quantitative analysis indicates that the dominant contribution to the yield strength derives from the dispersion strengthening mechanism by creation of fine Al6Fe and Al13Fe4 particles. The results in this work demonstrate that ultrafine microstructure can be obtained in a simple binary Al-Fe alloy as a result of the extremely high cooling rate during LPBF process, which offers a design strategy towards high-strength recyclable aluminum alloys.
•Nano-sized metastable Al6Fe particles are uniformly dispersed in SLM-processed Al–2Fe eutectic alloy.•Al–Al6Fe anomalous eutectic with spherical intermetallics is directly formed from the liquid phase.•Aging treatment promotes the transformation of Al6Fe phase to Al13Fe4 phase and the precipitation of supersaturated Fe atoms.•The dispersed Al6Fe and Al13Fe4 particles contribute to an ultimate tensile strength as high as 300 MPa of the Al–2Fe alloy.
Multimodal imaging‐guided photothermal therapy (PTT), for the therapy of cancer, based on a ferritin (FRT) nanocage loaded with the near‐infrared dye IR820 (designated DFRT) is demonstrated. The dual ...roles of DFRT (in imaging and PTT) are successfully balanced by using two different excitation wavelengths: 550 nm for high quantum‐yield fluorescence imaging on the one hand and 808 nm for photoacoustic imaging and PTT with high photothermal conversion efficiency on the other.
In this work, we proposed a novel modification technique to immobilize nanoparticles by the nanopores on a boron-doped diamond surface, preventing the aggregation of nanoparticles physically and ...improving the stability of nanoparticles layer by the anchoring effect. All the exposed surfaces of a bare boron-doped diamond were etched into nanoporous form and larger electrochemically active surface area was obtained on the porous boron-doped diamond electrode. The carbon black nanoparticles modified porous boron-doped diamond electrode showed good selectivity to separate the oxidation potential of three molecules, but led to an extra increase in the peak current of dopamine (DA). The carbon black/Nafion modified porous diamond electrode effectively suppress the oxidation current of ascorbic acid (AA), enhancing the sensitivity of DA. The dual layer treatment enables a wide linear range, 0.1–100 μM and a low limit of detection, 54 nM for DA detection, which is almost unaffected by the excess AA and uric acid (UA). At last, real sample tests of the carbon black/Nafion modified porous diamond electrode was validated by applying to the detection of DA in human serum and dopamine hydrochloride injection, which were found to be promising at our preliminary experiments. Additionally, the fabricated carbon black/Nafion modified porous diamond electrode also demonstrated good stability and long-term functionality.
Display omitted
•A novel modification on porous boron-doped diamond electrode for determination of dopamine was developed.•The elimination of the interference was realized and a low detection limit of 54 nM for DA was obtained.•Reproducibility of the CB-Nafion/p-BDD electrode in real sample and excess interferents was validated.•Excellent stability and long-term functionality of the CB-Nafion/p-BDD electrode were confirmed.
Hydrogen can contribute significantly to the energy mix of the near future, as it is an attractive replacement for fossil fuels due to its high energy density and low greenhouse gas emission. A ...fascinating approach is to use the polarization change of a ferroelectric due to an applied stress or temperature change to achieve piezo- or pyro-catalysis for both H2 generation and wastewater treatment. We exploit low Curie temperature (Tc) ferroelectrics for polarization-driven electrochemical reactions, where the large changes in polarization and high activity of a ferroelectric near its Tc provides a novel avenue for such materials. We present experimental evidence for enhanced water splitting and rhodamine B degradation via piezo-catalysis by ultrasonic excitation at its Tc. Such work provides an effective strategy for water splitting/treatment systems that employ low Tc ferroelectrics under the action of mechanical stress or/and thermal fluctuations.
Display omitted
•First demonstration of the positive impact of operating near Tc for piezo-catalysis•Ultrasound applied to achieve piezo-catalysis near Tc•High hydrogen production rate and degradation rate were achieved at the Tc•Piezo-catalysis is a new avenue for low Tc and lead-free ferroelectrics
Catalysis; Electrochemical Energy Production; Ceramics
In vivo tracking or in vitro real sample analysis by electrochemistry is one of the most straight and useful methods in biosensor field. However, surface biofouling of electrodes by non-specific ...protein adsorption is inevitable and usually leads to a decrease in sensitivity. Here, we developed a Nafion-coated porous boron-doped diamond (NAF/pBDD) electrode with hydrophobic nanostructures to minimize the biofouling effect and selectively detect dopamine (DA). Larger active area was obtained by this procedure compared to a bare diamond electrode. The as-prepared electrode shows excellent antifouling property and enrichment capacity toward selective detection of dopamine (DA). The low background current of the BDD electrode and the enhanced signals enables a lower detection limit, 42 nmol L
−1
, and a wider linear range, 0.1–110 μmol L
−1
, for determination of DA in human serum. Additionally, the facile modified electrode demonstrated renewable property and long-term stability due to the fact that the antifouling nanostructures belong to its own.
PDF
