The influence of pulse plating parameters on microstructure and properties of Ni-W-Si3N4 nanocomposite coatings

Nanosized silicon nitride (Si₃N₄) particles reinforced Nickel-tungsten composite coatings were deposited on the surface of C45 steel sheet by pulse electrodeposition. The effect of duty cycle, frequency, current pattern and presence of Si₃N₄ nanoparticles on microstructure, phases and corrosion resistance and mechanical properties of the coatings were investigated. The Si₃N₄ phase was incorporated into Ni-W alloy matrix uniformly and the inclusion content of in the coating was analyzed by energy dispersive x-ray spectrometer (EDS). The structure, microhardness and surface roughness of the coatings was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), Vickers micro-indenter and atomic force microscopy (AFM). The corrosion protection of steel by the coatings was evaluated by weight loss and electrochemical impedance spectroscopy (EIS). Corrosion rates of the coatings were determined using the Tafel polarization test. The results indicated that the duty cycle of 60%, pulse frequency of 1000 Hz, average current density of 5 A/dm⁻², and Si₃N₄ nanoparticles concentration of 30 g/L were the optimal plating conditions. The amount of Si₃N₄ particles incorporated into the coating that were produced under the optimum plating conditions was 2.1 wt%, and the microhardness was 1031 Hv as well as the crystallite size of this coating was 27 nm.     

Microstructural,mechanical and tribological properties of nanostructured YSZ coatings produced with different APS process parameters

Plasma sprayed ceramic coatings can be used in turbine engines as thermal barrier or abradable coatings, in order to improve the durability of the components as well as the efficiency. The presence of nanostructures, deriving from partial melting of agglomerated nanostructured particles, represents an interesting technological solution in order to improve their functional characteristics. In this work nanostructured yttria stabilized zirconia (YSZ) coatings were deposited by air plasma spraying (APS). The influence of the main process parameters on their microstructural, mechanical and tribological properties was investigated by scanning electron microscopy (SEM), indentation techniques at micro- and nano-scale and wear tests, respectively. Their porous microstructure was composed of well melted overlapped splats and partially melted nanostructured areas. This bimodal microstructure led to a bimodal distribution of the mechanical properties. An increase of plasma power and spraying distance was able to produce denser coatings, with lower content of embedded nanostructures, which exhibited higher elastic modulus and hardness as well as lower wear rate.     

以6063铝合金为基底的三价铬与锆杂化转化膜的制备及其电化学特征

引言传统上使用六价铬转化膜来提高铝及其他金如锌及钢铁的防腐蚀性能[1-2]。然而,六价铬有毒,在电器及电子工业中,欧盟RoHS法规禁止使用六价铬化合物[3]。     

漆酚缩醛亚胺环氧涂料的研制及其性能

本文利用甲醛与环氧树脂的多元胺固化剂二乙烯三胺、漆酚反应,先合成漆酚醛亚胺(PUFD),再与环氧树脂(ER)混合,使PUFD中的活泼氢与ER中的环氧基反应,制备PUFD/ER涂料。反应过程中多元胺链和环氧基反应时相互缠绕,形成分步互穿网络聚合物。PUFD/ER涂料兼具了漆酚和环氧树脂的优异性能,耐磨蚀,硬度高,柔韧性好,光泽度大。