Effects of reference materials on texture coefficients determined for a CVD α-Al2O3 coating

Abstract

α-Al2O3 coatings deposited onto cemented carbide tools by chemical vapor deposition (CVD), are widely employed in cutting applications due to their excellent wear resistance, thermal stability and chemical inertness. Technological advancements have allowed the control of crystallographic texture, enabling the exploration of anisotropic wear resistance of α-Al2O3. Within this study, a comprehensive microstructure characterization of an α-Al2O3 coating is presented, with the goal to provide useful guidelines for the determination of its crystallographic texture using texture coefficients (TCs). Electron backscatter diffraction (EBSD) and X-ray diffraction (XRD) pole figures were firstly used to determine the (001) fiber texture of the representative coating. TCs were then calculated, utilizing XRD intensities from three different reference materials (i.e. an α-Al2O3 coating powder, NIST SRM 676a and NIST SRM 1976b), for the same as-deposited coating. Based on the results obtained, a set of guidelines is advised for the determination of texture coefficients: (a) X-ray intensity acquisition only for symmetric θ/2θ scans, (b) removal of X-ray background intensity, (c) use of reflections that have a high peak to background X-ray intensity ratio, (d) application of peak fitting functions when overlaps occur, (e) exclusion of second order reflections at the presence of first order reflections, (f) texture coefficients provided should be accompanied by the respective coating thickness, and (g) use of an appropriate powder standard reference material.