Mapping of local lattice parameter ratios by projective Kikuchi pattern matching

Abstract

We describe a lattice-based crystallographic approximation for the analysis of distorted crystal structures via Electron Backscatter Diffraction (EBSD) in the scanning electron microscope. EBSD patterns are closely linked to local lattice parameter ratios via Kikuchi bands that indicate geometrical lattice plane projections. Based on the transformation properties of points and lines in the real projective plane, we can obtain continuous estimations of the local lattice distortion based on projectively transformed Kikuchi diffraction simulations for a reference structure. By quantitative image matching to a projective transformation model of the lattice distortion in the full solid angle of possible scattering directions, we enforce a crystallographically consistent approximation in the fitting procedure of distorted simulations to the experimentally observed diffraction patterns. As an application example, we map the locally varying tetragonality in martensite grains of steel. * a.winkelmann@lzh.de †

Improving EBSD precision by orientation refinement with full pattern matching

“…We observe that the orientation precision of the FPM method presented here approaches the level of HR transmission Kikuchi (TKD) measurements on the strain field of single dislocations (Yu et al ., 2019), where the spatial resolution of TKD is about an order of magnitude better than EBSD. The possibility to resolve fine orientational features by the FPM method demonstrated here suggests future investigations of additional strain effects via aprojective pattern matching approach that has been used for mapping the local tetragonality in martensite using low‐resolution patterns (Winkelmann et al ., 2018).…”

Tetragonality mapping of martensite in a high‑carbon steel by EBSD

“…In this context, electron backscatter diffraction (EBSD) is an attractive technique because it offers the possibility to determine the local crystallography of a microstructure with a resolution in the submicrometer range in a scanning electron microscope (SEM) [21]. Several studies have been recently presented for the EBSDbased analysis of tetragonality in martensite grains [22,23,16]. These investigations involved the matching of experimental, background corrected EBSD patterns to Kikuchi pattern simulations for a fixed set of tetragonalities [22], or the consistent deformation of a fixed reference simulation for a variable fit to local c/a ratios and general strain states [23].…”

Kikuchi pattern simulations of backscattered and transmitted electrons

“…Kikuchi diffraction simulations are also applied to estimate continuous parameters from experimental patterns. This includes the calibration of the geometrical setup, 17–20 the indexing and refinement of crystal orientations 8,21–27 and the quantification of local changes in lattice parameters, 28–31 including the possible role of defects 32 …”

“…Kikuchi diffraction simulations are also applied to estimate continuous parameters from experimental patterns. This includes the calibration of the geometrical setup, [17][18][19][20] the indexing and refinement of crystal orientations 8,[21][22][23][24][25][26][27] and the quantification of local changes in lattice parameters, [28][29][30][31] including the possible role of defects. 32 To improve the simulation-based pattern matching approaches, it is necessary to understand which experimental effects are relevant to be included in the theoretical models used in Kikuchi diffraction pattern simulations.…”