Abstract
Mapping crystal orientation has always been the domain of diffraction-based techniques. However, these measurements have limited throughput and require specialized equipment. In this work, we demonstrate crystal orientation mapping on chemically etched aluminum samples using a simple and inexpensive optical technique called directional reflectance microscopy (DRM). DRM quantifies surface reflectance as a function of illumination angle. We identify directional reflectance characteristics of grains with (111) out-of-plane orientation and infer their surface topography to calculate their underlying crystal orientation. We confirm the surface topography using atomic force microscopy and validate DRM orientation measurements with electron backscatter diffraction.
Highlights
Optical microscopy (OM) is one of the most common characterization techniques to analyze the surface microstructure of metals and metal alloys
Grains are color-coded according to the inverse pole figure (IPF) color scheme used in electron backscatter diffraction (EBSD) measurements [17]
directional reflectance microscopy (DRM) measurements were made with a 12-lm step size, with each pixel averaging the reflectivity of the area, whereas EBSD measurements were made with a similar step size (6 lm), but measuring only from a much smaller spot in the middle of each step rather than averaging the area
Summary
Optical microscopy (OM) is one of the most common characterization techniques to analyze the surface microstructure of metals and metal alloys. The crystal structure and orientation of such features cannot be directly assessed through OM because of its diffraction-limited spatial resolution [5, 6]. To acquire this information and investigate the relationships between materials structure and properties, researchers usually rely on diffraction-based techniques such as electron backscatter diffraction (EBSD) [7] or X-ray diffraction (XRD) [8]. Spiedel et al demonstrated the possibility of mapping the out-of-plane texture of etched polycrystalline nickel and aluminum (Al) by analyzing surface topography through laser confocal microscopy [9]. Oleksii et al demonstrated grain orientation mapping on Ramanactive materials using a polarized laser source [11]
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