Acquisition of partial grain orientation information using optical microscopy

Abstract

Optical microscopy (OM) is often the first technique used to characterize surfaces of materials because of its simplicity and low cost. However, the information obtained by OM is usually limited to the geometry and spatial distribution of microstructural features. We present an advanced OM technique to perform quantitative microstructure analysis of polycrystalline metals and to assess partial grain orientation information from measurements of reflectance over a range of incident light directions. Our technique relies on the collection of a series of optical micrographs under controlled illumination conditions. We find a marked directiondependence of reflectance and ascribe it to sub-micron facets on the surfaces of individual grains. These surface facets are, in turn, correlated to grain orientation. We automate our technique via digital processing and numerical analysis of micrographs, enabling it to generate a wealth of microstructure data while remaining simple to use and inexpensive to implement.

Stereometric characterization of kefir microbial films associated with Maytenus rigida extract

“…However, it is possible to obtain important information from the optical microscopy data of blends if the phases are present in micron size droplets or beads. In materials science, optical microscopy has many applications, especially for determination of grain size (H. Chen et al, 2017) and orientation (Hart et al, 2006; Seita et al, 2017). Therefore, AFM images were performed in order to overcome this limitation and obtain more accurate information on the surface of biofilms.…”

Crystallographic character of grain boundaries resistant to hydrogen-assisted fracture in Ni-base alloy 725

“…First, it opens the opportunity for improved lifetime predictions based on measurements of the number and distribution of BLIPs in individual components. Such predictions may be used to reduce the occurrence of unexpected failures by imposing service limits that are microstructure informed 69 , 78 . They may also be used to extend operating lifetimes by averting premature withdrawal of components from service due to overly conservative failure models.…”

Measuring crystal orientation from etched surfaces via directional reflectance microscopy

“…First, we segment the sample surface (Fig. 3a) by identifying areas where changes in the directional reflectance occur [12]. The segmented image contains a network of grain boundaries that separate all grains that can be resolved by DRM (Fig.…”

“…Here, we demonstrate a new method for identifying and analyzing orientation in a subset of grains on etched Al surfaces using an inexpensive light source and a simple optical microscope. This technique, based on directional reflectance microscopy (DRM) [12], involves the acquisition of a sequence of optical micrographs taken under varying illumination conditions. As a result of etching, the grains on the sample surface exhibit different orientation-dependent facets, which reflect light in specific directions.…”

“…This operation is performed in MATLAB and is similar, in principle, to the background subtraction process described in Ref. [12]. Here, however, the operation involves a division as opposed to a subtraction.…”