High resolution atomic scale characterization of dislocations in high entropy alloys: Critical assessment of template matching and geometric phase analysis

• Published in: Ultramicroscopy 2020-12, Vol.219, p.113134-113134, Article 113134
• Main Authors: Brenne, F., Mohammed, A.S.K., Sehitoglu, H.
• Format: Article
• Language: English
• Subjects: Displacement analysis; Geometrical phase analysis; High entropy alloy; Scanning transmission electron microscopy; Template matching
• ISSN: 0304-3991; 1879-2723
• DOI: 10.1016/j.ultramic.2020.113134

•Atomic scale displacement fields of dislocations within a HEA are characterized.•TeMA and GPA are assessed by comparison of experimental and simulated images.•The ascertainable maximum displacement is limited for both techniques.•The dislocation plane is directly obtained for small displacements only.•A methodology for burgers vector determination using two projections is introduced. The paper assesses the applicability of advanced atomic resolution displacement measurement techniques to characterize dislocation character in metallic materials using simulated images derived from anisotropic elasticity and actual measurements in high entropy alloys. We draw attention to two techniques: the real space method of template matching (TeMA) and the reciprocal space method of geometric phase analysis (GPA) and provide a critical assessment. These techniques have limitations for direct evaluation of full dislocations Burgers vector or when local displacements are exceeding 50% lattice spacing. This is clearly illustrated with simulated arctangent displacement profiles reminiscent of dislocation cores. An approach for circumventing this limitation is suggested in the form of a nearest neighbor correction. Additionally, a methodology for determination of the Burgers vector is introduced on the basis of a vectorial rendering of the displacement field upon consideration of two zone axis measurements and applied to TeMA and GPA. The experimental results conform to the Burgers vector of a full lattice dislocation in the FCC crystal structure of the High-Entropy Alloy (HEA). The comparison of simulated and experimental images proves the efficacy of the HR-TEM (High Resolution Transmission Electron Microscopy) displacement mapping techniques while pointing to the need for caution in case of large displacements.