Phase Identification Using EBSD in the SEM: What Can be Done Today and What we Hope to do Tomorrow

Abstract

Phase identification using electron backscatter diffraction (EBSD) in the SEM has become a useful and important tool for the characterization of crystalline materials. Phase identification is accomplished using EBSD in the following manner. First, a high quality camera must be added to the SEM. Suitable cameras use slow scan CCD imagers coupled either by a lens or a fiber optic bundle to a phosphor screen that is situated near the sample. A EBSD pattern is collected and EDS or WDS is used to determine qualitatively the chemistry of the area. An automated routine is then used to extract the positions and widths of the lines in the pattern followed by a calculation of the unit cell volume. This information coupled with the chemistry of the sample is then used to search a database of crystal structures. Currently, the ICDD's Powder Diffraction file of over 100,000 compounds is used. Once a list of potential matches is found the patterns are indexed and then simulated to demonstrate that the phase has been identified. This paper will demonstrate use of EBSD for phase identification and then will speculate on future developments.A particularly nice application of EBSD is the use of the technique for the identification of phases that form in welds. Figure 1a is an EBSD pattern obtained from a acicular phase in a superalloy weld. The phase was determined to be primarily Ti and Ni. Analysis of the patterns showed that the phase is Ni3Ti. Figure 1b shows the simulation for Ni3Ti overlaid on the experimental pattern demonstrating that the phase has been identified.