Summary The importance of angular resolution in EBSD analyses is discussed based on an Inconel 718 sample containing several populations of recrystallized grains, with subtle differences in dislocation contents. Classical EBSD analyses (with angular resolution in the range of 0.5–1°) do not allow for distinguishing recrystallized grains grown dynamically or post‐dynamically. The angular resolution of EBSD orientation and misorientation data can be significantly improved (down to about 0.1–0.2°) either using more sophisticated Kikuchi pattern indexing methods and/or using the recently proposed LLASS denoising filter (Local Linear Automatic Smoothing Splines). Then the coexistence of both dynamically and post‐dynamically recrystallized grains in the sample can be confirmed and quantified. ECCI images unambiguously confirm the conclusions drawn from the analysis of improved angular resolution EBSD data, and furthermore reveal the presence of thermal stress induced dislocations with typical patterns in water quenched Inconel 718 recrystallized grains. Lay Description EBSD is widely used to study recrystallization phenomena. Conventional EBSD is nevertheless not able to distinguish dynamic recrystallized grains from post‐dynamic recrystallized grains which differ by subtitle differences in dislocation contents. In this paper, we show that improving the orientation precision of EBSD data by means of different methods allows distinguishing these two recrystallized grains populations. Analyses and discussion are based on an Inconel 718, a famous Nickel‐based superalloy in aeronautic.
An implementation of smoothing splines is proposed to reduce orientation noise in electron backscatter diffraction (EBSD) data, and subsequently estimate more accurate geometrically necessary dislocation (GND) densities. The local linear adaptation of smoothing splines (LLASS) filter has two advantages over classical implementations of smoothing splines: (1) it allows for an intuitive calibration of the fitting versus smoothing trade‐off and (2) it can be applied directly and in the same manner to both square and hexagonal grids, and to 2D as well as to 3D EBSD data sets. Furthermore, the LLASS filter calculates the filtered orientation gradient, which is actually at the core of the method and which is subsequently used to calculate the GND density. The LLASS filter is applied on a simulated low‐misorientation‐angle boundary corrupted by artificial orientation noise (on a square grid), and on experimental EBSD data of a compressed Ni‐base superalloy (acquired on a square grid) and of a dual austenitic/martensitic steel (acquired on an hexagonal grid). The LLASS filter leads to lower GND density values as compared to raw EBSD data sets, as a result of orientation noise being reduced, while preserving true GND structures. In addition, the results are compared with those of filters available in the MTEX toolbox.
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