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In order to improve the surface properties of hot work mold steel, the influence and mechanism of laser quenching, plasma nitriding and laser quenching/plasma nitriding composite treatment process on the friction, wear and corrosion resistance of the modified layer of H13 steel were studied. The surface morphology, surface chemical composition and microstructure of samples with different heat-treated were characterized by optical microscope, scanning electron microscope and energy dispersive spectrometer. Results showed that the composite treatment process could significantly improve the friction and wear resistance of the modified layer, and improve the corrosion resistance of the material surface. Compared with the single laser quenching and single nitriding treatment, the average friction coefficient of the modified layer after composite treatment declined significantly, the self-corrosion potential was remarkably increased, which indicated that the wear resistance and corrosion resistance of the modified layer after composite treatment were improved dramatically.

Three kinds of metal atoms with different valence electronic configurations, Bi (6s26p3), Y (4d15s2), and Ce (4f15d16s2), were selected to investigate the effect of A-site (La3+) doping on electronic band structure, photoelectric properties, and photocatalytic performance of LaFeO3 perovskite. It was identified that the Bi doped LaFeO3 presented significantly improved photocatalytic activity towards the reduction of CO2, while the Y or Ce doped LaFeO3 displayed decreased photocatalytic activity compared to the pristine LaFeO3. It was revealed that doping of all the three metal atoms resulted in narrowed band gap and thus extended light absorption of LaFeO3 by lowering its conduction band minimum (CBM). The recombination rate and mobility of the charge carriers were represented by the relative effective mass (D) between holes and electrons for pristine and A-site doped LaFeO3. The doping of Bi resulted in increased D value, attributed to the Bi 6s electron states at the valence band maximum (VBM), and thus promoted separation and transfer of the charge carriers and improved photocatalytic activity of LaFeO3. In contrast, the doping of Ce resulted in significantly decreased D value, induced by the highly localized Ce 4f hole states at the CBM, and thus higher recombination rate of the charge carriers and decreased photocatalytic activity of LaFeO3. Furthermore, the Y doped LaFeO3 with a slightly decreased D value presented slightly increased recombination rate of the charge carriers and thus decreased photocatalytic activity. Such a work provides new insights into the A-site doping in LaFeO3 perovskite, which should be helpful for optimizing the electronic band structure and activity of perovskite-type photocatalysts at atomic level. [ABSTRACT FROM AUTHOR]

AISI 316L stainless steel has received considerable attention as a common material for key ball valve components; however, its properties cannot be improved through traditional phase transformation, and fretting wears the contact interface between valve parts. A carburized layer was prepared on the surface of AISI 316L stainless steel by using double-glow low-temperature plasma carburization technology. This study reveals the effect of double-glow low-temperature plasma carburization technology on the fretting wear mechanism of AISI 316L steel under different normal loads and displacements. The fretting wear behavior and energy dissipation of the AISI 316L steel and the carburized layer were studied on an SRV-V fretting friction and wear machine with ball–plane contact. The wear mark morphology was analyzed by using scanning electron microscopy (SEM), the phase structure of the carburized layer was characterized with X-ray diffractometry (XRD), and the wear profile and wear volume were evaluated with laser confocal microscopy. The carburized layer contains a single Sc phase, a uniform and dense structure, and a metallurgically combined matrix. After plasma carburizing, the sample exhibited a maximum surface hardness of 897 ± 18 HV0.2, which is approximately four times higher than that of the matrix (273 ± 33 HV0.2). Moreover, the surface roughness was approximately doubled. The wear depth, wear rate, and frictional dissipation energy coefficient of the carburized layer were significantly reduced by up to approximately an order of magnitude compared with the matrix, while the wear resistance and fretting wear stability of the carburized layer were significantly improved. Under different load conditions, the wear mechanism of the AISI 316L steel changed from adhesive wear and abrasive wear to adhesive wear, fatigue delamination, and abrasive wear. Meanwhile, the wear mechanism of the carburized layer changed from adhesive wear to adhesive wear and fatigue delamination, accompanied by a furrowing effect. Under variable displacement conditions, both the AISI 316L steel and carburized layer mainly exhibited adhesive wear and fatigue peeling. Oxygen elements accumulated in the wear marks of the AISI 316L steel and carburized layer, indicating oxidative wear. The fretting wear properties of the AISI 316L steel and carburized layer were determined using the coupled competition between mechanical factors and thermochemical factors. Low-temperature plasma carburization technology improved the stability of the fretting wear process and changed the fretting regime of the AISI 316L steel and could be considered as anti-wearing coatings of ball valves. [ABSTRACT FROM AUTHOR]

The community smart governance based on technologies such as big data, cloud computing, Internet of Things, artificial intelligence, etc., creates a broader space for development and improvement of future community in the new era and new situation, and also draws a vibrant picture for improving the effectiveness of community governance. The article takes the first top ten cases of community smart governance as the research object. Based on 169 concepts derived from the application of grounded theoretical methods, 19 initial categories are determined, and top-level design, resource construction, application scenarios, and governance efficiency as the key elements of community smart governance are extracted. Finally, by constructing a theoretical analysis framework for the key elements of community smart governance, it provides a reference basis for the smarter future community governance. [ABSTRACT FROM AUTHOR]