Formation of ceramic alumina nanocomposite coatings on aluminium for enhanced corrosion resistance

Plasma electrolytic oxidation (PEO) has been considered as a novel technique to form ceramic nanocomposite coatings on aluminium and magnesium alloys for corrosion protection. However, a systematic study of the effect of process parameters on the properties of the coatings has not been well demonstrated. In the present study, aluminium was treated by PEO at various treatment time, current density, temperature and concentration of NaOH and Na₂SiO₃ and their effect on the surface properties of the coatings has been investigated systematically. It was found that the temperature and treatment time were the major factors affecting the thickness and growth. The coatings mainly consisted of α-alumina, γ-alumina and Al₂(SiO₃)₃. The ceramic composite coatings with best corrosion resistance were obtained at higher current density, lower temperature, moderate treatment time and optimum concentration of NaOH and Na₂SiO₃. The crystallite size of the composite coating was found to be in nanometer scale (9–131 nm).     

A2Zr2O7型稀土锆酸盐热障涂层研究进展

综述了国内外稀土锆酸盐热障涂层在制备技术,纳米涂层,涂层结构及涂层的热物理性能、力学性能及热腐蚀性能等方面的研究成果,讨论了稀土锆酸盐热障涂层在每个方面研究存在的不足。指出未来应该进一步改善稀土锆酸盐涂层的制备工艺及后处理工艺,提高涂层的结合强度,延长涂层的服役寿命,改善涂层耐腐蚀、抗烧结等性能;开发新的涂层制备工艺,重点研究各类纳米稀土锆酸盐涂层的性能;进一步提高涂层的隔热效果、服役温度及工作寿命。     

纯镁超声微弧氧化生物涂层植入体内4周的降解行为

研究纯镁及其超声微弧氧化生物涂层种植体植入动物股骨干内的短期降解过程。利用电化学工作站测定试样在模拟体液中极化曲线。术后4周,取兔股骨干的组织进行扫描电镜观察(SEM)及锥形束检测(CBCT)观察种植体降解状况。结果表明,纯镁与超声微弧氧化生物涂层都发生了降解,在骨组织表面及镁基体的表面几乎同时发生反应,在金属-骨界面形成紧密相邻的降解层、新生骨层,并可见少量的不连续的纤维结缔组织,超声微弧氧化镁生物涂层的腐蚀降解速率及对周围骨组织的刺激明显小于纯镁基体。纯镁基体及超声微弧氧化涂层试样周围的骨组织变化符合正常骨组织的愈合过程,超声微弧氧化生物涂层显示出更好的生物相容性及降解性。     

纳米石墨改性ZM5镁合金微弧氧化陶瓷层摩擦磨损性能

添加纳米石墨颗粒的硅酸盐溶液中制备ZM5合金微弧氧化陶瓷层,利用SEM、EDS和XRD分析了涂层的微观形貌、成分及物相组成,用球-盘干磨损试验对涂层的室温摩擦磨损行为进行研究。结果表明,纳米石墨改性微弧氧化陶瓷层主要由Mg2SiO4、少量的MgO、Mg和C相组成,石墨以机械形式分散于陶瓷层中并起到减摩作用。4.9N载荷下体积磨损率为9.19×10-5 mm3/Nm,是无石墨微弧氧化陶瓷层的1/3,ZM5基体的1/14;9.8N载荷下体积磨损率为1.44×10-4 mm3/Nm,是无石墨微弧氧化陶瓷层的2/5,ZM5基体的1/8,与无石墨微弧氧化陶瓷层相比显著提高了镁合金基体的耐磨性,且其室温干摩擦磨损机理为疲劳磨损,磨痕呈疲劳剥落形貌。     

Effect of current density on micro‐arc oxidation of Q235 steel and corrosion resistance in liquid Pb‐Bi

An attempt has been made to improve the corrosion resistance in liquid Pb‐Bi by micro‐arc oxidation (MAO), and the effects under different current densities on the corrosion resistance of the coatings were discussed. Scanning electron microscope, energy dispersive spectrometer, and X‐ray diffraction were used to analyze the surface morphology and phase constituents of the MAO coatings produced under different current densities. The corrosion resistance of the coatings was evaluated by studying the element changes and morphology evolution. The results show that the compactness of the ceramic coating decreases with the current density increasing. In contrast to the performance of matrix metal, the ceramic coating exhibited a much better corrosion resistance in liquid Pb‐Bi. Moreover, the ceramic coating produced under current density of 10 A/dm ² shows the best corrosion resistance.     

Laser remelting of plasma-sprayed yttria partially stabilized zirconia coatings

A plasma-sprayed 8 wt.% yttria partially stabilized zirconia coating doped with 3 wt.% SiO₂ was remelted by laser. The microstructure of the as-sprayed and laser-remelted coatings was characterized by scanning electron microscopy (SEM), electron probe microanalysis (EPMA), transmission electron microscopy (TEM), and x-ray diffraction (XRD). The effect of laser remelting on the hardness, wear resistance, and thermal shock resistance of the coatings was also studied. The laser-remelted coating consists of fine solidification grains without the presence of pores and cracks. The elements are uniformly distributed in the laser-remelted coating. Nontransformable tetragonal (t′) phase is predominant in the laser-remelted coating with a small amount of cubic phase. Laser remelting greatly enhanced the hardness, wear resistance, and thermal shock resistance of the coatings, and should find more applications.     

Fabrication and characterization of Al2O3-metal composite coating on steel plate with nonpressure combustion synthesis

Al2O3-metal composite coatings with different reactants and diluents were fabricated on mild steel plate with nonpressure combustion synthesis process. The coat-ings were characterized by means of X-ray diffraction, scanning electron microscopy, and energy-dispersive spec-trometry, respectively. Thermal shock tests were carried out to determine the bond strength of the coating with the steel substrate. The results indicate that the coating is composed of α-A1203, α-（Fe-Cr） and Al2SiO5 as the main phases. It is found that the coating with the diluents of Al2O3-SiO2 and transition layer of Al2O3-Cr presents the hi.ghest hardness of 2270 HV0.2 and the lowest porosity of 3.93 %. Owing to a metallurgical bond of the coating-to-substrate, the coating exhibits a good thermal shock resistance.     

Characterization of plasma electrolytic oxidation coatings formed on Mg–Li alloy in an alkaline silicate electrolyte containing silica sol

We investigate the influence of silica sol addition on the ceramic coatings of Mg–Li alloy by plasma electrolytic oxidation (PEO) in an alkaline silicate electrolyte. Scanning electron microscopy, X‐ray diffraction, X‐ray photoelectron spectroscopy, and energy dispersive spectroscopy are employed to characterize the microstructure and composition of the ceramic coatings. The anti‐corrosion behavior of the ceramic coatings is evaluated by potentiodynamic polarization measurements in conjunction with electrochemical impedance analysis. The ceramic coating formed in the electrolyte containing silica sol contains SiO₂ and Mg₂SiO₄ phase and has more uniform morphology and higher corrosion resistance than that formed in the electrolyte without addition of silica sol.     

地面重型燃气轮机及其热障涂层的研究进展与发展趋势

国际公认的重型燃气轮机制造尖端技术之一—热障涂层技术,高温下通常面临CMAS(CaO-MgO-Al₂O₃-SiO₂)腐蚀、氧化、相变与烧结等问题,其抗CMAS腐蚀性等关键性能极大地影响涂层寿命,提高热障涂层的性能刻不容缓。对重型燃气轮机用热障涂层的研究进展与发展趋势进行全面总结与分析。首先介绍国内外重型燃气轮机的现状及发展趋势、热障涂层的系统结构、材料和几种典型的制备工艺,然后针对高温下燃气轮机热障涂层遇到的一些问题,对其隔热性、抗氧化性及抗热震性等关键性能的研究进展进行综述,最后分类详述热障涂层的CMAS腐蚀机理及其防护研究进展。综述热障涂层的几种关键性能,提出热障涂层的性能与其材料、结构及制备工艺密切相关,据此总结归纳提高热障涂层性能的方法,为热障涂层性能的提高提供参考依据,以弥补燃气轮机热障涂层领域目前缺乏这类综述文章的不足。     

淫羊藿苷含量对Mg/UMAO/CS/IC涂层性能的影响

为了研究淫羊藿苷含量对镁/超声微弧氧化/壳聚糖/淫羊藿苷（Mg/UMAO/CS/IC）涂层性能的影响,并提高纯镁的耐蚀性,采用电泳沉积（EPD）和UMAO技术在纯镁基体上制备Mg/UMAO/CS/IC涂层。采用扫描电子显微镜（SEM）、X射线衍射（XRD）、原子力显微镜（AFM）和傅立叶变换红外光谱（FTIR）对涂层的特征进行分析。对不同样品在模拟体液中进行了电化学阻抗和动电位极化的腐蚀行为研究。结果表明：当IC含量为0.4 g/L时CS/IC层具有较好的封孔效果。添加不同IC含量的Mg/UMAO/CS/IC涂层均由Mg、MgO、CS和Mg₂SiO₄组成。不同IC含量涂层的自腐蚀电流密度（i_corr）比Mg至少都低一个数量级,能为镁基底提供更有效的保护。IC含量为0.4 g/L时Mg/UMAO/CS/IC涂层的耐蚀性更好,自腐蚀电流密度（1.667×10^-6 A/cm²）最小。Mg/UMAO/CS/IC涂层可有效解决纯镁在临床骨内固定应用上降解过快的问题。     

Thermal barrier coating application of zircon sand

Naturally occurring zircon sand was plasma spray coated on steel substrates previously coated with NiCrAlY bond coat. The coatings were characterized for their microstructure, chemical composition, thermal shock resistance, and the nature of structural phases present. The as-sprayed coatings consisted of t-ZrO₂ (major phase), m-ZrO₂, ZrSiO₄ (minor phases), and amorphous SiO₂. These coatings, when annealed at 1200 °C/1.44 × 10⁴s yielded a ZrSiO₄ phase as a result of the reaction between ZrO₂ and SiO₂. Dramatic changes occurred in the characteristics of the coatings when a mixture of zircon sand and Y₂O₃ was plasma spray coated and annealed at 1400 °C/1.44 × 10⁴s. The t-ZrO₂ phase was completely stabilized, and these coatings were found to have considerable potential for thermal barrier applications.     

Effect of hybrid aluminum dihydrogen phosphate on the corrosion resistance of PTFE composite ceramic coatings

In this study, the polytetrafluoroethylene (PTFE) composite ceramic coatings with hybrid aluminum dihydrogen phosphate (AP) are prepared on AISI 304L stainless steel by spraying and heat curing to improve the corrosion resistance of the coatings. AP is hybridized with methyltriethoxysilane (MTES), and the structure of the hybrid AP is characterized by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. Contact angle tests, scratch tests, and electrochemical experiments are used to investigate the corrosion behavior of composite ceramic coatings. In addition, scanning electron microscopy is used to examine the microscopic morphology of the coatings after corrosion to investigate the mechanism of the hybrid AP on the corrosion resistance of the composite ceramic coatings. The findings reveal that MTES successfully hybridizes with AP and implants the –CH₃ hydrophobic group in AP, which improves the hydrophobicity of composite coatings. The corrosion potential of hybrid AP coatings all move in a positive direction, and the corrosion current density is lower than that of unhybridized AP coatings. The corrosion current density of the coating is about 2.931e?008 A/cm² when the MTES content is 5 wt%, which is 20% less than that of the unhybridized AP coating. Results indicate hybrid AP can significantly improve the corrosion resistance of PTFE composite ceramic coatings with the best corrosion resistance occurring when the content of MTES is 5 wt%.     

Anti-corrosion microarc oxidation coatings on SiCP/AZ31 magnesium matrix composite

The corrosion-resistant ceramic coatings up to 80 μm thick were fabricated on SiC_P/AZ31 magnesium matrix composite by microarc oxidation (MAO) technique in Na₃PO₄ + KOH + NaF solution. The microstructure, composition and phase constituent of ceramic coatings were analyzed by SEM and XRD, and the electrochemical corrosion behaviour of coatings was evaluated by the electrochemical polarization method. The thicker coating is compact and displays a good adhesion to the composite substrate. The ceramic coatings consist of MgO, Mg₂SiO₄, MgF₂, Mg₃(PO₄)₂, furthermore, a few residual SiC phases were also found in the coatings by means of SEM observation and EDX analysis. Most of SiC reinforced particles in the oxidized composite substrate have transformed into the oxides under microarc discharge sintering, but a few residual SiC reinforcements in the MAO coatings have not disrupted the continuity of coatings. So the corrosion resistance of the SiC_P/AZ31 composite is greatly improved by MAO surface treatment, however, the corrosion resistance of coated composite also depends on the coating thickness.     

An Investigation into the Corrosion Behavior of MgO/ZrO<Subscript>2</Subscript> Nanocomposite Coatings Prepared by Plasma Electrolytic Oxidation on the AZ91 Magnesium Alloy

Plasma electrolytic oxidation (PEO) of AZ91 Mg alloys was performed in ZrO₂ nanoparticles containing Na₂SiO₃-based electrolytes. The phase composition and the microstructure of PEO coatings were analyzed by x-ray diffraction and scanning electron microscopy followed by energy dispersive spectroscopy. Pitting corrosion properties of the coatings were investigated using cyclic polarization and electrochemical impedance spectroscopy tests in a Ringer solution. The results showed the better pitting corrosion resistance of the composite coating, as compared to the oxide one, due to the thickened inner layer and the decrease in the surface defects of the composite coating. Also, the PEO process decreased the corrosion current density from 25.06 µA/cm² in the Mg alloy to 2.7 µA/cm² in the oxide coating and 0.47 µA/cm² in the composite coating.     

An ultrasonic testing method for detecting delamination of sprayed ceramic coating

The adhesion strength of thermal sprayed coatings is relatively low, and they sometimes tend to delaminate from the substrate during operation. In particular, sprayed ceramic coatings for thermal barriers, such as ZrO₂, often delaminate because of thermal shock; therefore, ceramic coatings are often submitted to thermal shock tests. A nondestructive inspection method using ultrasound to detect the delamination of sprayed coating was proposed. In this study, a coating model was made with acrylic plates, and an ultrasonic test was applied to investigate the precision of detecting delamination by the ultrasonic testing method. Results indicate that delamination more than 1mm in diameter can be detected by the ultrasonic testing method. Moreover, the delaminating process of sprayed coatings under thermal shock tests can be detected by this method.     

Enhancement of Functional Ceramic Coating Performance by Gas Tunnel Type Plasma Spraying

A high-precision plasma system has been pursued for advanced thermal processing. The gas tunnel type plasma jet device developed by the author exhibits high energy density and also high efficiency. Among its various applications is the plasma spraying of ceramics such as Al₂O₃ and ZrO₂. The performance of these ceramic coatings is superior to conventional ones. Properties such as the mechanical and chemical properties of the zirconia coatings were reported in previous studies. In this study, the enhancement of the performance of functional ceramic coatings by the gas tunnel type plasma spraying method was carried out using different powders. Results show that the alumina/zirconia composite system exhibited improvements of mechanical properties and corrosion resistance. The alumina/zirconia composite coating has the potential for use as a high functionally graded thermal barrier coating. Another application of the gas tunnel type plasma is for surface modification of metals. As an example, TiN films were formed in 5 s and, thick TiN coatings were easily obtained by gas tunnel type plasma reactive spraying.     

AZ31B合金热化学反应热喷涂复相陶瓷涂层制备及性能

采用机械球磨和PVA（聚乙烯醇）造粒制成喷涂复合粉末,采用热化学反应火焰喷涂技术,在镁合金AZ31B表面制备Al2O3,基复相陶瓷涂层．利用x射线衍射（XRD）、扫描电镜（SEM）分析了喷涂复合粉末和复合陶瓷涂层的组成及形貌,并对涂层的热震性能、致密性、显微硬度和耐磨性进行测试．结果表明,复合粉末经12h球磨后有化学反...     

SiON/SiO2复合膜层对太阳能电池阵板间电缆的表面改性及其耐空间环境性能

在空间站工作的太阳电池阵板间电缆上下表面为聚酰亚胺薄膜,在低轨运行时会受到原子氧的强烈侵蚀,需要采取措施对其进行保护。采用射频磁控溅射法在电缆表面制备了颗粒尺寸均匀、排列致密的SiO₂膜层。通过表征空间环境试验前后样品发现由于电缆表面的凸起颗粒等缺陷无法完全被SiO₂膜层覆盖,导致原子氧会对缺陷位置产生侵蚀作用。采用全氢聚硅氮烷溶液对板间电缆基底进行表面改性处理,制备的聚硅氧氮烷涂层（SiON）可以有效地覆盖电缆基底表面的凸起颗粒等缺陷,使得其上溅射的SiO₂膜层表面光滑平整。经原子氧暴露试验,SiON/SiO₂层内部没有受到其侵蚀作用,可以防止原子氧对电缆基底的破坏。经多次冷热循环试验,SiON/SiO₂复合膜层仍然具备良好的结构特性与结合性能。     

Si-Mo-SiO2 oxidation protective coatings prepared by slurry painting for C/C-SiC composites

Three types of Si-Mo-SiO₂ coatings: two single-layered ones by different slurry paintings and a final sintering, and three-layered one by triple paintings followed by sintering each time, have been fabricated on the surface of C/C-SiC composites. The coatings were composed of SiC, MoSi₂, Si and SiO₂. The two single coatings had a microstructure with many pinholes and deep microcracks and had no obvious protection for C/C-SiC composites in air in the range of 1273-1673 K. While the triple Si-Mo-SiO₂ coating had a microstructure with much less defects and could provide more than 100 h protection at 1473-1673 K in air and kept intact in the course of 50 cycles of thermal shock test between 1673 K and 373 K. The excellent anti-oxidation ability and thermal shock resistance of the triple Si-Mo-SiO₂ coating can be attributed to its relatively integral microstructure and the self-sealing of microcracks during oxidation.     

ZM5镁合金无铬前处理化学镀镍层的性能

采用优化的Na4P2O7+Na2SO4+NaNO3体系的化学蚀刻无铬前处理化学镀镍工艺,在ZM5镁合金上制备Ni-P镀层。利用扫描电镜、能谱仪、X射线衍射仪分析镀层的微观形貌、成分和相结构。通过电化学方法和摩擦磨损试验评价了镀层的耐蚀性和耐磨性。结果表明:无铬前处理工艺制备的镀层中P的质量分数为12.90%。与ASTM标准的含铬前处理工艺得到的镀层的耐蚀性和耐磨性相比,无铬前处理得到的镀层的自腐蚀电位为-0.506V,腐蚀电流密度为2.132×10-6 A/cm2,接近ASTM工艺含铬前处理得到的镀层的耐蚀性能;同时其磨损率为3.056×10-4 mg/s,与ASTM工艺的1.778×10-3 mg/s相比,其抗摩擦磨损性能明显优于含铬前处理的镀层。无铬前处理化学镀镍显著提高了ZM5镁合金的耐蚀性和耐磨性。