The deposition of alumina on thermal barrier coatings can effectively avoid hot corrosion and increase durability. Al 2 O 3 coatings were prepared on an yttria-stabilized zirconia (YSZ) substrate by plasma chemical vapor deposition (CVD). The effects of microwave power (P M ) and total pressure (P tot ) on the crystalline phase and microstructure of Al 2 O 3 coatings were investigated, and the effect of the mechanism on the deposition rate was also analyzed. The α-Al 2 O 3 coatings with a needle-like microstructure were formed at a higher P M and P tot , whereas the γ-phase coatings exhibited a cauliflower-like microstructure at a lower P M and P tot . A maximum deposition rate (R dep ) of 58 μmh −1 was obtained, which is significantly higher than those of conventional CVD methods. K E Y W O R D S alumina, chemical vapor deposition, coatings | 1357 ZHANG et Al. How to cite this article: Zhang S, Zheng L, Wei G, et al. Structural investigation of Al 2 O 3 coatings by PECVD with a high deposition rate. Int J Appl Ceram
Silver coating has an excellent antibacterial activity but low mechanical properties, e.g., microhardness. In order to improve simultaneously the antibacterial activity and surface hardness of titanium alloys, TiAlN/Ag multiple coatings with different gradient distributions in thickness were prepared on titanium alloys by unbalanced magnetron sputtering. The coatings with gradient thickened TiAlN–Ag cosputtered upper layers had a much stronger antibacterial activity, 99.82% in antiseptic Escherichia coli, than those with the gradient thinned upper layers. With increasing gradient cycles of the multiple coatings, the antibacterial activity decreased, whereas the hardness increased. The alternate growth of TiAlN and TiAlN–Ag layers may repeatedly provide an excellent comprehensive antibacterial activity (99.23% for Escherichia coli) and hardness (two times TC4 alloy) for a long term.
This paper presents a novel parametric model of marine propellers based on Non-Uniform Rational B-Splines. It involves eight parameters and five categories of spanwise parameter distributions, which are utilized for determining hydrofoil and blade shapes. 20 different hydrofoils and 5 types of well-known marine propellers are employed to detect the accuracy of the proposed parametric model. Furthermore, a propeller optimization problem was addressed with the aid of the parametric model. In the propeller optimization problem, a common AU-series propeller is treated as the baseline propeller. The proposed parametric model is used for the representation and deformation of the propeller geometric model. A hydrodynamic performance evaluation model is developed based on gene expression programming. Also, non-dominated sorting genetic algorithm II is used in the applications of the propeller optimization problem. The results demonstrate that the accuracy of the proposed parametric model satisfies the engineering requirements well, and a propeller with higher efficiency than the baseline propeller can be derived by settling the propeller optimization problem.
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