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Soil-bentonite vertical cut-off wall is an emergency technique used for contaminant control in geo-environmental engineering, high-density polyethylene (HDPE) geomembrane (GM) with an extremely low-permeability coefficient is expected to enhance the contaminant barrier effect of the vertical cut-off wall. To evaluate the barrier performance of the composite barrier composed of GM and soil-bentonite mixture towards organic contaminant, while also quantitively revealing the impact of GM defects and placement, a one-dimensional transport model for organic contaminants in composite barrier is solved under semi-infinite boundary conditions. The proposed transport model is validated by numerical simulations using COMSOL Multiphysics 5.4, and the effects of GM defect rate, placement within the composite isolation wall, and contact level with soil-bentonite on contaminant transport behavior are further studied. The results show that as the average frequency of GM defects increases from 2.5 to 50 holes per hectare, the breakthrough time of organic contaminants through composite barrier decreases by almost 70%. Poor contact level between GM and soil-bentonite mixture may reduce the breakthrough time of the composite cut-off wall by 65%. Although the selection of GM placement has limited impact on the transient flux of contaminants, it does affect the total flux of contaminants over a certain period of time. The effects of permeability coefficient, effective diffusion coefficient, distribution coefficient, and hydraulic head of the composite cut-off wall can be considered by the proposed analytical solution, which would provide guidance and reference for the design and service performance evaluation of the composite cut-off wall.

In this study, aluminum matrix composites reinforced with micro-TiN are fabricated via the selective laser melting (SLM) technique. The effects of the TiN content on the densification, microstructure evolution, crystal textures, and mechanical properties are investigated. The results show that the relative density of composite samples with 0-3 wt. % TiN is higher than 98% and further increasing the TiN content results in a decrease in their relative density. The TiN particles are distributed uniformly and wetted with the AlSi10Mg matrix in the form of a graded interfacial layer. The TiN particles refine the matrix grains and significantly weaken the preferred (001) texture by promoting a heterogeneous nucleation process. Compared with those of the AlSi10Mg alloy, the microhardness, tensile strength and wear resistance of the TiN/AlSi10Mg composite are improved. The excellent mechanical properties of the Al matrix composites are attributed to the dispersion strengthening of the TiN particles and the fine-grain strengthening of the matrix. The optimal TiN content is found to be 3 wt. %, at which the fabricated samples exhibit excellent mechanical performance (132.4?4.1 HV for hardness and 379.7?4.6 MPa for tensile strength) with a low friction coefficient of 0.49.

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In this paper, Ti6Al4V+3 wt.% TiB2 composite powder was used as a raw material to synthesize TiB whiskers in situ and prepare composites reinforced with TiB/Ti6Al4V whiskers by selective laser melting (SLM). The effects of process parameters on the properties of TiB/Ti6Al4V samples were systematically studied. The evolution of the microstructure, including the formation and regulation of whiskers, and the effects on mechanical properties were discussed. The results showed that during the SLM process, adjusting the energy density effectively inhibited cracking in the TiB/Ti6Al4V samples. The TiB2 particles acted as nucleation centers to significantly refine the grains during processing and reacted with elemental Ti to form a needle-like TiB network at the grain boundaries, which strengthened the whiskers. Additionally, TiB played a role in dispersion strengthening. Compared with Ti6Al4V, the microhardness of TiB/Ti6Al4V was 430.6?11.45 HV, an increase of 27.9%, and the wear volume of the sample was 0.85?10-3 mm3, a decrease of 62.64%.