Orientation Determination of Low Symmetry Materials Using Computational Polarized Light Optical Microscopy

The structure of materials can have a big impact on the properties and performance of the material. A variety of methods are used by materials scientists and engineers to study the crystallographic orientation of grains in bulk metal. Computational polarized light microscopy (CPLM) is proposed as a method for partial orientation determination for metals with anisotropic structure, such as a-titanium. CPLM is a low cost, easy-to-use orientation mapping method, which can be used as an alternative to methods such as EBSD. When a-titanium grains are illuminated with polarized light, the reflected intensity of light of each grain differs depending on the orientation of the grain. An intensity profile can be obtained for a grain illuminated with linearly polarized light at different rotations. From this intensity profile, the partial orientation of the grain, which describes inclination and azimuth of the grain’s c-axis, can be determined. The c-axis orientation of grains determined using the CPLM method is compared to the known orientation obtained from EBSD. Comparison between the two show reasonable agreement between the methodologies. Results also suggest polarization aberration exists across the field of view of the microscope setup. An experiment was conducted to isolate changes in reflected intensity caused by grain orientation from that which was caused by polarization aberration in the optical chain. In addition to the experimental work, an idealized physics-based forward model was developed for the CPLM method. This model is used to simulate the theoretical intensity profile for a given grain orientation. While area for improving both the experimental setup and forward model exist, there

are interesting potential for future applications with preliminary results shown, including performing texture analysis for samples with localized texture as well as applications to different materials systems.