The high melting point and strong chemical bonding of NbB2 pose a great challenge to the preparation of high-density nanostructured NbB2 composite coating. Herein, we report a novel, simple, and efficient method to fabricate in-situ NbB2-NbC-Al2O3 composite coating by plasma spraying Nb2O5-B4C-Al composite powder, aiming at realizing the higher densification and ultra-fine microstructure of NbB2 composite coating. The microstructure and properties of in-situ NbB2-NbC-Al2O3 composite coating were studied comparatively with ex-situ NbB2-NbC-Al2O3 composite coating (plasma spraying NbB2-NbC-Al2O3 composite powder). The reaction mechanism of Nb2O5-B4C-Al composite powder in plasma jet was analyzed in detail. The results showed that the in-situ nanostructured NbB2-NbC-Al2O3 composite coating presented a lower porosity and superior performance including higher microhardness, toughness and wear resistance compared to the plasma sprayed ex-situ NbB2-NbC-Al2O3 coating and other boride composite coatings. Densification of the in-situ NbB2-NbC-Al2O3 coating was attributed to the low melting point of Nb2O5-B4C-Al composite powder and the exothermic effect of in-situ reaction. The superior performance was ascribed to the density improvement and the strengthening and toughening effect of the nanosized phases. The in-situ reaction path could be expressed as: Nb2O5 + Al → Nb + Al2O3, and Nb + B4C → NbB2 + NbC.

Under the background of the normalization of COVID-19 prevention and control and the rapid development of e-commerce, community group buying has occupied the market by providing low-priced, fast, and green consumer goods, but with it, the logistics and distribution volume of goods has also increased sharply. In order to reduce environmental pollution and the carbon emissions caused by transportation in the community group buying logistics distribution, it is necessary to investigate a suitable method to optimize vehicle distribution routes and reduce carbon emissions. Taking the lowest total costs of logistics and distribution and the smallest carbon emissions, this article introduces soft time window function and carbon emissions parameters, takes the delivery of goods from the community group buying distribution center in Wu’an Town, Hebei Province to customer points in 14 townships as an example, an optimization model for the distribution route of low carbon vehicles for community group buying based on improved genetic algorithm was constructed, AHP-EW fusion technology was used to calculate carbon emissions and cost weights, and compared with the traditional genetic algorithm and ant colony algorithm two typical heuristic algorithms, the feasibility of the proposed model and the advantages of the improved algorithm are verified, and the research results showed that it can reduce the costs and carbon emissions of vehicle distribution, provide decision-making reference for community group buying logistics enterprise distribution, and promote energy conservation and environmental sustainable development.

With technological revolutions and new rural revitalization strategies, rural e-commerce logistics and agricultural modernization are becoming the focus of society. The purpose of the current study is to measure the coupling coordination state of regional rural e-commerce logistics and agricultural modernization, to analyze the obstacles to coordinated development, to forecast the trend, and to propose policy suggestions for coordinated development. Based on the theory of system coordinated development, this paper selects representative indicators reflecting regional rural e-commerce logistics and agricultural modernization, and constructs a coordinated development measurement index system. This paper also constructs a coupling coordination-obstacle degree model, adopting Handan City, Hebei Province as an example, using the data obtained from 2010 to 2019 to measure the coordinated development status of rural e-commerce logistics and agricultural modernization; and analyzes the obstacles affecting coordinated development. By introducing the grey prediction GM (1,1) model and by applying it to the research, the results show that the model is feasible, and the coordinated development level of rural e-commerce logistics and agricultural modernization in Handan City presents a fluctuating upward trend. The prediction results show that the coordinated development of rural e-commerce logistics and agricultural modernization will achieve good coordination in 2024, and relevant development suggestions are proposed. The research can provide some decision-making references for establishing the measurement model, an obstacle-factor analysis, and a trend prediction for the coordinated development of regional rural e-commerce logistics and agricultural modernization.

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