Statistical analysis of dislocations and dislocation boundaries from EBSD data

Abstract

Electron BackScatter Diffraction (EBSD) is often used for semi-quantitative analysis of dislocations in metals. In general, disorientation is used to assess Geometrically Necessary Dislocations (GNDs) densities. In the present paper, we demonstrate that the use of disorientation can lead to inaccurate results. For example, using the disorientation leads to different GND density in recrystallized grains which cannot be physically justified. The use of disorientation gradients allows accounting for measurement noise and leads to more accurate results. Misorientation gradient is then used to analyze dislocations boundaries following the same principle applied on TEM data before. In previous papers, dislocations boundaries were defined as Geometrically Necessary Boundaries (GNBs) and Incidental Dislocation Boundaries (IDBs). It has been demonstrated in the past, through transmission electron microscopy data, that the probability density distribution of the disorientation of IDBs and GNBs can be described with a linear combination of two Rayleigh functions. Such function can also describe the probability density of disorientation gradient obtained through EBSD data as reported in this paper. This opens the route for determining IDBs and GNBs probability density distribution functions separately from EBSD data, with an increased statistical relevance as compared to TEM data. The method is applied on deformed Tantalum where grains exhibit dislocation boundaries, as observed using electron channeling contrast imaging.

Texture control of 316L parts by modulation of the melt pool morphology in selective laser melting

“…A strong intragranular misorientation is visible in the grains through the continuous color gradients of each grain. Moussa et al (2017) attributed it to the presence of geometrically necessary dislocations that induce a local lattice rotation. Those dislocations can originate from the rapid solidification occurring in SLM.…”

The influence of the cube component on the mechanical behaviour of copper polycrystalline samples in tension

“…All recent studies using this equation thus make use of this value for the constant k [46]. The misorientation is then most often represented by the KAM (Kernel Average Misorientation) parameter by considering 1 to 3 EBSD measurement steps for (we have considered 3 steps in the present case, in order to obtain a satisfactory precision [47]). This parameter is an estimate of the local misorientation, calculated as the average of the misorientations between one given point and its nearest neighbors, excluding those which are not located within the same grain.…”

Substructure Development and Damage Initiation in a Carbide-Free Bainitic Steel upon Tensile Test

“…Instead, the bainite is able to accumulate the strain by formation not only of continuous misorientations that accumulate with distance, but also a subgrain structure, as illustrated in Figure 6c. This kind of subgrain structure is usually reported to increase its related misorientation as strain increases [39]. The stagnation value in the austenite is around 5.4 and 6.1 • µm −1 for the 5 and 10 • angular thresholds.…”