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The sea cucumber Apostichopus japonicus (A. japonicus) is a benthic invertebrate with a quasi-cylindrical body and several rows of papillae (conical prominence) on its body wall. As nutrient recyclers, A. japonicus plays a fundamental role in marine ecosystems and is one of the most important commercial aquaculture species in eastern Asia. Despite its ecological and economical importance, little is known concerning the flow characteristics surrounding A. japonicus on the organism scale. Research on the detailed flow structure at such a scale may serve as a significant step toward understanding the transport of sediment and nutrients in the vicinity of A. japonicus. This study sets up the D3Q27 multiple-relaxation-time lattice Boltzmann method to obtain the three-dimensional flow structure around an individual A. japonicus placed at the bottom of a flat-bed channel. The numerical model is validated by a water flume experiment. The flow patterns exhibit distinctive features at three different angles of attack (0 ° , 4 5 ° , 9 0 ° ). The increasing inflow velocity (0. 1 m/s , 0. 25 m/s , 0. 4 m/s) brings no fundamental change to the structure of flow fields but induces more small-scale vortices and larger velocity fluctuations. This study investigates the complex turbulent flow fields around the A. japonicus and provides new insight for future studies on the interaction between water flow and A. japonicus. • A lattice Boltzmann model was built to study flow structure around A. japonicus. • Clusters of U-shaped vortices are produced on the surface of A. japonicus. • The flow patterns exhibit distinctive features at three different angles of attack. • The influence of the incoming flow velocity was investigated. [ABSTRACT FROM AUTHOR]

In this paper, a simple and efficient technique of interlayer interface Ar+ etching is presented to regulate the microstructure and properties of the TiSiN/TiAlN coating deposited by arc ion plating. SEM, AFM, XRD, and EIS of the TiAlN coating indicate that Ar+ bombardment can reduce the roughness and porosity density. HR-TEM reveals the presence of epitaxial growth at the interlayer interface. The TiSiN/TiAlN coating exhibits high bonding force (L c3 around 118.7 N) and excellent toughness (CPR s around 2230.2 N2) at − 300 V etching. The wear rate and COF of the coating are reduced to 4.26 × 10−5 mm3∙N−1∙m−1 and 0.295. The results demonstrate that interlayer interface Ar+ etching can effectively optimize the interlayer quality and enhance the wear resistance of the multilayer coating. [Display omitted] • This article reports a simple and effective process to control the structure and tribological properties of the coating through the interlayer interface Ar+ etching. • At the etching energy of –300 V, the crystalline sizes of TiAlN (111) and (200) are the smallest, 22.90 and 21.07 nm respectively. The etched interlayer interface has a low roughness and dense structure, which provides the epitaxial growth of the coating. • Meanwhile, Ar+ etching improves the strength and toughness of the coating (H/E* and H3/E*2 ratios around 0.097 and 0.280 GPa). • Improving the quality of the interlayer interface and mechanical properties is conducive to enhancing the wear resistance of the double-layer coating (CPR s around 2230.2 N2, COF 0.295, and wear rate 4.26×10−5 mm3∙N−1∙m−1). [ABSTRACT FROM AUTHOR]

In this paper, the design and preparation of infrared stealth coatings adapted to wear environments by multi-arc ion plating is researched. The coating has a micrometer and nanometer scale multilayer structure which has been verified by SEM and TEM. At the micrometer scale, the coating has a sandwich layer structure of nitrides/Cr/nitrides. At the nanometer scale, the nitride coating exhibits a nano-multilayer structure of (AlCrSiN/CrN) n. The modulation period of the (AlCrSiN/CrN) n /Cr/(AlCrSiN/CrN) n coating is adjusted by changing the substrate revolution speed (0.5–2.0 r/min) to optimize infrared stealth and wear resistance. At the revolution speed of 1.5 r/min, the XRD pattern indicates that the Al-Cr-N crystalline sizes of the (111) and (200) planes are the smallest (11.68 and 14.54 nm, respectively). When the cycle period n is set to 6 (r=1.5 r/min), HR-TEM shows that the AlCrSiN layer exhibits semi-coherent epitaxial growth with the CrN layer. The multiscale multilayer design results in the lowest infrared emissivity of the coating at wavelengths of 3–5 and 8–14 μm (0.235 and 0.133, respectively). Furthermore, the coating has excellent scratch and wear resistance (L c 3 =85.1 N, 25℃-2.42×10−6 mm3/(N·m), and 550 ℃-4.81×10−5 mm3/(N·m)). The design concepts of multilayer and multiscale provide a framework for the application of coatings in wear and infrared composite environments. [Display omitted] • Low infrared emissivity can be obtained by adjusting the modulation period of (AlCrSiN/CrN) n /Cr/(AlCrSiN/CrN) n coating. • The coating offers both wear resistance and excellent adhesive strength. • The coating has excellent wear resistance at 550 ℃, showing low friction coefficient and wear rate. [ABSTRACT FROM AUTHOR]