Conventional and nanostructured NiCoCrAlY coatings were deposited using the high-velocity oxy-fuel thermal spraying technique. The nanostructured NiCoCrAlY powder feedstock for the coatings was produced by the ball-milling method. The microstructures of the as-received and nanostructured powders as well as their developed coatings were investigated by x-ray diffraction, a field-emission scanning electron microscope equipped with energy-dispersive x-ray spectroscopy, and a transmission electron microscope. Williamson–Hall measurements were also carried out to estimate the crystalline size of the powders and coatings. For the evaluation of the oxidation kinetics, the free-standing coating specimens were subjected to short- and long-term isothermal and cyclic oxidation at 1000 and 1100 °C, respectively, under a laboratory air atmosphere. The results indicated that the as-received NiCoCrAlY coating had parabolic oxidation behavior in short- and long-term exposure tests. For the nanostructured NiCoCrAlY coating, in contrast, the long-term oxidation kinetics deviated from parabolic behavior and showed instead sub-parabolic rate behavior. The obtained results also revealed that the nanostructured NiCoCrAlY coating had greater oxidation resistance to both isothermal and cyclic conditions on account of the formation of a dense and slow-growing Al2O3 layer on the coating surface.

中文翻译：

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HVOF 喷涂 NiCoCrAlY 涂层的等温和循环氧化行为：常规和纳米结构涂层的比较研究

使用高速氧燃料热喷涂技术沉积常规和纳米结构的 NiCoCrAlY 涂层。用于涂层的纳米结构的 NiCoCrAlY 粉末原料是通过球磨法生产的。通过 x 射线衍射、配备能量色散 x 射线光谱的场发射扫描电子显微镜和透射电子显微镜研究了原样和纳米结构粉末及其开发的涂层的微观结构。还进行了 Williamson-Hall 测量以估计粉末和涂层的结晶尺寸。为了评估氧化动力学，独立涂层试样在实验室空气气氛下分别在 1000 和 1100 °C 下进行短期和长期等温和循环氧化。结果表明，原样的 NiCoCrAlY 涂层在短期和长期暴露测试中具有抛物线氧化行为。相反，对于纳米结构的 NiCoCrAlY 涂层，长期氧化动力学偏离抛物线行为，而是表现出亚抛物线速率行为。所得结果还表明，由于在涂层表面形成致密且缓慢生长的 Al2O3 层，纳米结构的 NiCoCrAlY 涂层在等温和循环条件下均具有更高的抗氧化性。