The origin of color inhomogeneity in anodized titanium at the microscopic scale is investigated. Oxide layers were produced by galvanostatic anodizing in sulfuric acid on commercial Ti–6Al–4V substrates, with and without HF/HNO etching prior to anodizing. The crystallographic orientations of the Ti–6Al–4V substrates were determined using Electron Backscatter Diffraction (EBSD) before anodizing. The chemical composition of the oxide thin films was characterized using X-ray Photoelectron Spectroscopy (XPS). The oxide thin films were observed optically using a digital microscope. The internal morphology of the oxide layers was observed through a Scanning Transmission Electron Microscope (STEM) on Focused Ion Beam (FIB) lamella preparations, taken at the boundary of two differently colored areas on anodized Ti–6Al–4V samples. By characterizing both the substrate and the oxide layer, a correlation was established between the crystallographic orientations of the underlying Ti–6Al–4V substrate and the morphology of the oxide layer. It is shown that crystallographic orientations of the phase of the substrate close to the basal plane (0001) lead to a porous oxide layer, resulting in a blue color. For other grains and the grains of the substrate, the oxide layer is dense and exhibits a yellow color. The development of an optical model to simulate color, accounting for the porosity of the oxide layer, confirms the correlation between porosity and color.

中文翻译：

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Ti-6Al-4V基体晶体取向对阳极氧化氧化物薄膜形貌和光学性能的影响

研究了微观尺度阳极氧化钛颜色不均匀的根源。氧化层是通过在商用 Ti-6Al-4V 基材上的硫酸中进行恒电流阳极氧化而产生的，在阳极氧化之前进行或不进行 HF/HNO 蚀刻。 Ti-6Al-4V 基材的晶体取向在阳极氧化前使用电子背散射衍射 (EBSD) 确定。使用 X 射线光电子能谱 (XPS) 表征氧化物薄膜的化学成分。使用数字显微镜对氧化物薄膜进行光学观察。通过扫描透射电子显微镜 (STEM) 在聚焦离子束 (FIB) 薄片制备物上观察氧化层的内部形态，在阳极氧化 Ti-6Al-4V 样品上两个不同颜色区域的边界处拍摄。通过表征基底和氧化物层，在下面的 Ti-6Al-4V 基底的晶体取向和氧化物层的形态之间建立了相关性。结果表明，接近基面 (0001) 的基底相的晶体取向导致多孔氧化物层，从而产生蓝色。对于其他晶粒和基材的晶粒，氧化层致密并呈现黄色。开发模拟颜色的光学模型，考虑了氧化物层的孔隙率，证实了孔隙率和颜色之间的相关性。