Characterization of Coatings by SEM Based Microdiffraction
The behaviour of a coating is directly related to its microstructure as well as the crystal structure and composition of different phases that are formed in the deposition process. A comprehensive study of the microstructure and local phase assembly in coatings would help in arriving at structure-property correlations that can help understand the coating behaviour. SEM-based diffraction techniques provide a simple method for obtaining local crystallographic information without the need for complex synchrotron sources. In this study, we present a method for characterization of coatings using SEM-based microdiffraction which involves the combined use of the EDS and EBSD capabilities, citing a Ti-Al-Cr-N multilayer coating as an example. The different layers in the coating were observed and the electron beam focused in each region to first obtain Energy Dispersive Spectra and electron backscatter patterns (EBSPs). The elemental constituents were identified from EDS maps and used to shortlist the possible phases present. The diffraction pattern for each possible phase was then calculated and the EBSPs of the observed and calculated patterns were compared for the closest match. The identified phase was then used as an input to set up EBSD scans across the coating. A qualitative picture of the compositional variation in multilayer coatings was obtained that could help in arriving at the exact stoichiometry of the different layers. Hence, SEM-based microdiffraction allows identification of local crystallographic phases and composition, permitting detailed microstructural studies that would find special application in the study of coatings.
Asim Tewari, Satyam Suwas, Dinesh Srivastava, Indradev Samajdar and Arunansu Haldar
R. C. Gundakaram and S. P. Pemmasani, "Characterization of Coatings by SEM Based Microdiffraction", Materials Science Forum, Vols. 702-703, pp. 570-573, 2012