Wet abrasive wear behavior of WC-based cermet coatings prepared by HVOF spraying

In this study, three kinds of WC-based cermet coatings including WC–CoCr coating, WC–Ni coating and WC–Cr₃C₂–Ni coating were prepared by the high-velocity oxygen-fuel (HVOF) spraying process. Scanning electron microscopy (SEM), energy disperse spectroscopy (EDS) and Vickers hardness tester were used to analyze the microstructure and mechanical properties of these coatings. The WC–CoCr coating presented the highest average microhardness of 1205 HV_0.3, and then followed by the WC–Cr₃C₂–Ni coating (1188 HV_0.3) and the WC–Ni coating (1105 HV_0.3). The abrasive wear behavior of the WC-based coatings under the conditions of different applied loads and sediment concentrations were studied by a wet sand-rubber wheel tester. The results indicated that the abrasive wear loss rates of all the coatings increased with the increment of applied load or sediment concentration. In addition, the coatings with higher microhardness appeared to have higher abrasive wear resistance. The abrasive wear resistance of the WC-based coatings was 4–90 times higher than that of AISI 304 stainless steel under the same testing condition. The abrasive wear mechanism of the WC-based coatings was deduced to be the extrusion and removal of binder phases, as well as the fragmentation and peel-off of hard phases.     

SiC nanoparticles incorporation in electroless NiP-Graphene oxide nanocomposite coatings

The presence of SiC nanoparticles within the Graphene oxide (GO) incorporated electroless deposited NiP layers (NiP-GO) on carbon steel substrate was studied in this work. The effect of co-deposition of GO nanoplatelets and/or SiC nanoparticles on the morphology and structure of the heat-treated NiP coatings were investigated by scanning electron microscope and X-ray diffraction, respectively. The results revealed that the heat-treated NiP and NiP–SiC coatings consisted of Ni and Ni₃P phases, whereas the NiP-GO also contains the intermediated Ni₂P and Ni₁₂P₅ metastable phases due to the incomplete precipitation of Ni₃P. Such metastable phases are significantly decreased by the incorporation of SiC nanoparticles in NiP-GO coatings. The mechanical properties of the coatings were characterized by microhardness measurement and “pin on disk” wear test. The corrosion tests were conducted in aqueous 3.5 %wt NaCl using electrochemical measurement for Ni–P, NiP-GO, NiP–SiC, and NiP-GO-xSiC coatings. By co-deposition of SiC nanoparticles, the hardness of NiP-GO is significantly increased and the wear loss is reduced, especially at a high sliding distance during the wear test. The corrosion behavior of the NiP-GO coatings containing different amounts of SiC nanoparticles has been investigated.     

双态组织高Nb-TiAl合金的缺口敏感性

通过对圆棒状缺口试样和无缺口光滑试样进行单向拉伸试验,研究了双态组织高Nb-TiAl合金的缺口敏感性。研究表明,缺口根半径R≥0. 5 mm的U型试样和缺口角度60°、R≥1 mm的V型试样的抗拉强度RmN都大于光滑试样的抗拉强度Rm,缺口敏感度NSR均大于1,合金对缺口不敏感。当缺口类型相同时,缺口敏感性随缺口根半径R的减小而增大; V型缺口敏感性大于U型缺口;对于V型缺口试样,当R=0. 5 mm时,其NSR在0. 98～1. 03之间,RmN在Rm附近波动,易出现缺口敏感。     

环氧树脂涂层表面亲水性对微藻黏附性能的影响

在固体材料表面黏附成膜是微藻细胞的一种生理特性。近些年基于微藻生物膜的生物过程，如生物膜贴壁培养和防附着技术受到了很多关注。微藻在固体材料表面的黏附受藻细胞与材料表面之间的相互作用的影响，建立黏附强度与材料表面性质参数间的关系对于通过材料选择来强化或控制微藻生物膜具有非常重要的意义。本工作的目的是揭示和明确材料亲疏水性对微藻黏附的影响，提出了一种双酚A环氧(EP)树脂表面亲疏水改性的方法。通过将亲水性的二乙醇胺(DEA)或疏水性的聚甲基聚硅氧烷(PMHS)加入到EP树脂中反应，EP树脂表面水接触角在36.80?~98.34?范围内可通过加入不同量的DEA或PMHS实现任意可调，材料的表面水接触角与DEA或PMHS加入量之间有线性关系。重要的是这种改性方法获得的材料，其形貌、结构、表面粗糙度等表面性质几乎没有变化，从而在研究和关联微藻黏附量与材料表面亲疏水性(表面水接触角)之间的关系时可以排除亲疏水性之外的其他表面性质的影响；其次，考察了小球藻和栅藻在不同亲疏水性材料表面的黏附行为，结果表明小球藻和栅藻在亲水性和疏水性材料表面均能黏附成膜，但在亲水性材料表面黏附更多更快；建立了微藻最大黏附容量与材料表面接触角之间关联关系，表明微藻最大黏附容量随材料表面水接触角的增大而线性降低，栅藻的表面黏附容量比小球藻大。     

双时效对Ti-4Al-5Mo-6Cr-5V-1Nb合金显微组织和力学性能的影响

研究了固溶、固溶后单时效以及固溶后双时效处理对Ti-4Al-5Mo-6Cr-5V-1Nb合金组织和力学性能的影响。结果表明,820℃下固溶0.5 h后,合金中的α相完全溶解;单/双时效合金的硬度均随时效时间增加先升高后降低;合金经300℃/8 h+500℃/8 h双时效处理后可达到4580 MPa的峰值硬度(HV),1462 MPa抗拉强度以及3.4%延伸率,其强度比原始合金高6%,也高于单时效合金。界面能计算结果表明ω相使α相形核的阻力降低50%,促进了α相的析出并细化α板条,从而提升合金的硬度,强度及塑性。     

表面微结构自抛光防污涂层的制备与性能研究

为了研究表面微结构与自抛光的协同防污效果，将具有吸水溶胀能力的微球加入到自抛光树脂中，通过交联反应制备了表面微结构自抛光防污涂层，考察了涂层浸水过程中表面微结构形貌、溶胀、自抛光性能和抑制小球藻附着性能。研究结果表明：涂层自抛光过程中，微结构形貌的变化随微球含量的增加而更加明显；涂层溶胀率与微球的含量正相关，自抛光率与可水解单体含量正相关，但可水解单体含量过大时，涂层溶胀与自抛光成相互制约关系；小球藻附着率随微球含量的增加而增大，随可水解单体含量的增加而下降，当微球分散液质量分数为 10%、可水解单体质量分数为 40%时，涂层抑制小球藻附着的效果最佳。     

一种基于双重ddPCR的肉制品中牛源性成分的定量分析方法

将低价肉类原料掺入高价肉制品是一种典型的肉类掺假方式，为准确鉴别牛肉及牛肉制品的真伪，建立一种基于双重微滴式数字聚合酶链式反应（droplet digital polymerase chain reaction，ddPCR）的牛源性成分定量分析方法。通过对14 种动物的Beta-actin单拷贝基因序列进行分析，设计牛源性特异性引物、探针与动物源性成分通用引物、探针并建立双重ddPCR体系，推导出牛源性成分质量与其特异性扩增拷贝数之间的计算公式，对牛源性成分进行定量检测该方法得到牛源性成分质量M牛（mg）与其特异性扩增拷贝数浓度C牛（copies/μL）之间的计算公式为M牛=0.033C牛＋2.37，对已知牛肉质量的混合肉样品与不同部位的牛肉样品进行检测，结果显示牛肉定量检测值与实际质量基本一致。同时拷贝数相对含量可辅助判断肉制品中是否存在非牛源性的其他动物源性成分掺假。对市售样品的检测发现，存在目标肉样含量不达标以及不同程度的动物源性成分等掺假现象，说明该检测方法可为牛肉制品掺假量化判定和混合源性产品分级鉴定提供技术支撑。     

Performance analysis of large-scale MIMO system for wireless backhaul network

In this paper, we present a performance analysis of large-scale multi-input multi-output (MIMO) systems for wireless backhaul networks. We focus on fully connected N nodes in a wireless meshed and multi-hop network topology. We also consider a large number of antennas at both the receiver and transmitter. We investigate the transmission schemes to support fully connected N nodes for half-duplex and full-duplex transmission, analyze the achievable ergodic sum rate among N nodes, and propose a closed-form expression of the achievable ergodic sum rate for each scheme. Furthermore, we present numerical evaluation results and compare the resuts with closed-form expressions.