Preparation of superhydrophobic and wear-resistant surface on TC4 titanium alloy by combination of masking, chemical etching, and anodizing
MA Ning;SUN Kailun;SUN Guoyan;AVIC Shenyang Aircraft Company Limited;[Objective] To enhance the overall mechanical properties of superhydrophobic surfaces on TC4 titanium alloy through a composite processing strategy. [Method] A hierarchical and progressive complex structure was constructed via a three-step process: 1) creating an arrayed protective pattern on the surface of TC4 titanium alloy using a masking technique; 2) fabricating micro-scale structures by chemical etching; and 3) generating nano-scale features via anodization. The wettability measurement, scanning electron microscopic(SEM) observation, anti-icing test, corrosion resistance test, wear resistance test, and impact resistance test were carried out for comparing the performances of superhydrophobic surfaces prepared by four methods, namely single chemical etching, single anodization, chemical etching–anodization, and masking–chemical etching–anodization. [Result] The superhydrophobic surface formed by chemical etching had a contact angle of 153.0° and a sliding angle of 7.6°. The superhydrophobic surface prepared by anodization method had a contact angle of 155.4° and a sliding angle of 5.2°. The superhydrophobic surface fabricated by chemical etching and anodization without masking assistance had a contact angle of 157.6° and a sliding angle of less than 2.0°. The superhydrophobic surface constructed by the combination of masking, chemical etching, and anodization had a contact angle of 163.1° and a sliding angle of 4.5°. The TC4 titanium alloy surfaces treated by the combination of two or three methods had better hydrophobicity than that treated only by chemical etching or anodization. The superhydrophobic surfaces prepared by the four methods, especially by two composite processing methods, all showed good anti-icing properties and superior corrosion resistance to the untreated TC4 titanium alloy. The superhydrophobic surface with a hierarchical protective structure maintained superhydrophobicity(contact angle >150°, sliding angle ≈ 10°) after 18 linear abrasion cycles and withstood a sand falling impact of 400 g. [Conclusion] Compared with the superhydrophobic surfaces prepared by single-step methods, the superhydrophobic surface with a hierarchical and progressive structure prepared by the masking–chemical etching–anodization approach has better overall hydrophobicity, corrosion resistance, wear resistance, and impact resistance. The mask-assisted composite process also outperforms the mask-free one in mechanical properties.
Properties of phosphate-based micro-arc oxidation coatings on TC4 titanium alloy via mixture uniform design
SHAO Zhuqian;MA Ying;OU Kaiqi;WANG Hao;KANG Shuai;[Objective] The effects of component ratios in a phosphate-based micro-arc oxidation(MAO) electrolyte on the microstructure, corrosion resistance, and wear resistance of MAO coatings on TC4 titanium alloy were studied by mixture uniform experiments, aiming to identify an optimal electrolyte formulation. [Method] Ten groups of electrolytes with varying mass concentration ratios of Na3PO3, KF, and NaOH were designed via mixture uniform method. Micro-arc oxidation was carried out on TC4 titanium alloy. The morphology, phase composition, corrosion resistance, and tribological properties of MAO coatings were characterized using scanning electron microscopy(SEM), X-ray diffraction(XRD), electrochemical workstation, and friction and wear tests. [Result] The properties of MAO coating were significantly influenced by electrolyte composition. The MAO coating obtained with a mass ratio of Na3PO3, KF, and NaOH of 0.03:0.63:0.34 exhibited compact structure, high content of rutile TiO2, excellent corrosion resistance in both acidic and neutral media, and superior wear resistance. Under the high-load(5 N) and low-frequency(1 Hz) condition, although the MAO coating eventually experienced wear failure, it effectively delayed the damage to the substrate by mitigating the generation of fatigue pits and abrasive particles. Under low-load(0.5 N) and high-frequency(10 N) conditions, the formation of a tribo-oxide layer reduced the friction coefficient to 0.5, and the MAO coating remained intact without being worn through. [Conclusion] The mixture uniform design effectively optimizes the component ratios of the MAO electrolyte, significantly enhancing the corrosion and wear resistance of MAO coatings on TC4 titanium alloy. The optimized formulation yields MAO coatings with excellent friction-reducing and anti-wear properties under low-load and high-frequency conditions, making them suitable for fretting wear service environments.
Comparative study on corrosion resistance of micro-arc oxidation coatings on titanium alloy in different acidic environments
OU Kaiqi;MA Ying;SHAO Zhuqian;WANG Hao;[Objective] To study the effect of the presence or absence of fluoride additive and the variation of sodium phosphate concentration in the electrolyte on the structure and properties of micro-arc oxidation(MAO) coatings on titanium alloy, and to investigate the differences of corrosion resistance and characteristics of the coatings in nitric acid(HNO3) and hydrofluoric acid(HF) media. [Method] MAO coatings were prepared on the surface of TC4 titanium alloy in phosphate-based electrolytes with and without fluoride additive. The thickness, roughness, morphology, phase constitution, elemental distribution, and chemical states of MAO coatings were characterized by using eddy current thickness meter, scanning electron microscope(SEM), laser scanning confocal microscope(LSCM), X-ray diffractometer(XRD), X-ray photoelectron spectrometer(XPS), and electron probe X-ray micro-analyzer(EPMA), respectively. The corrosion resistance of MAO coatings was evaluated through dropping corrosion test. [Result] The addition of fluoride additive or an increase in sodium phosphate concentration enhanced the coating compactness and increased the content of corrosion-resistant phases such as rutile TiO2, Al2O3, and amorphous oxides. The MAO coatings exhibited better corrosion resistance in HNO3 than in HF. The coatings prepared with potassium fluoride showed superior corrosion resistance in both acids. A sodium phosphate concentration of 16 g/L yielded the optimal corrosion resistance. [Conclusion] The incorporation of fluoride additive and the increase in sodium phosphate concentration enhance the compactness, chemical composition, and phase structure of MAO coatings on TC4 titanium alloy, thereby improving their corrosion resistance. In HNO3, corrosion occurs mainly through consumptive attack, where coating compactness plays a critical role; in HF, penetration-dominated corrosion prevails, and corrosion resistance of MAO coatings depends primarily on elemental composition and phase structure.
Preparation and performance characterization of superhydrophobic and antibacterial nanocomposite coating on microarc-oxidized 5083 aluminum alloy
LU Kecheng;YANG Zhanhua;YANG Hongchi;ZHAO Qizhong;LAI Huajun;GAN Weijiang;XU Zebing;CHEN Zhiwu;MO Ran;HAO Chenggang;WANG Zhongmin;Guangxi Academy of Sciences;[Objective] To improve the corrosion resistance of 5083 aluminum alloy, a superhydrophobic and antibacterial composite coating was fabricated on its surface. [Method] The aluminum alloy was treated by micro-arc oxidation initially, and then sprayed with an epoxy paint containing silane-modified TiO2 and ZnO nanoparticles, forming a ca.400 μm-thick composite coating. The surface morphology and phase constitution of the micro-arc oxidation film and composite coating were examined using scanning electron microscope(SEM) and X-ray diffractometer(XRD), while the corrosion resistance, hydrophobicity, and antibacterial performance of the coating were tested by potentiodynamic polarization measurement, contact angle measurement, and plate count method. [Result] The composite coating prepared at a TiO_2-to-ZnO mass ratio of 1:1 showed the optimal corrosion resistance with a water contact angle up to 164.12° and a sliding angle as low as 2.10°. The antibacterial rates of the composite coating against Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa were 99.32%, 99.85%, and 91.17%, respectively. [Conclusion] The combination of micro-arc oxidation and nanocomposite coating technologies greatly enhances the corrosion resistance, hydrophobicity, and antibacterial performance of 5083 aluminum alloy.
Engineering application of cyanide-free silver electroplating technology in aviation field
LI Xuemin;ZHANG Di;GUO Yuchao;CUI Bin;ZHANG Chong;MAO Linwei;MA Kun;LI Zhenzhen;ZHANG Qi;AECC Beijing Hangke Engine Control System Technology Ltd.;[Objective] This study aims to develop a cyanide-free silver electroplating process with stable bath performance, excellent coating properties, ease of wastewater treatment, and maintenance costs not exceeding those of cyanide silver electroplating, thereby promoting the construction of cyanide-free silver electroplating production lines and its engineering application. [Method] Alkaline cyanide-free silver electroplating was carried out on substrates commonly used in aviation components. The bath stability, appearance, thickness, adhesion, sulfur resistance, and hydrogen embrittlement of Ag coating were characterized and compared with those of cyanide silver electroplating. [Result] The cyanide-free silver electroplating bath exhibited good stability. The deposition rate of cyanide-free silver electroplating was slightly lower than that of cyanide silver electroplating, but sufficient to meet production demands. The obtained Ag coating exhibited a silvery white appearance with a slight yellowish tint and a uniformly compact microstructure. Its adhesion, sulfur resistance, and hydrogen embrittlement resistance were complied with the requirements specified in the aeronautical industry standard HB 5051–1993 Quality Inspection of Silver Coatings. [Conclusion] The developed cyanide-free silver electroplating process can replace traditional cyanide silver electroplating and is suitable for engineering applications in aviation field.
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