Quantification of dislocation structure heterogeneity in deformed polycrystals by EBSD

Abstract

Plastic deformation in polycrystalline materials involves a complex interaction of dislocations with defects in the lattice. The geometrically necessary component of the dislocation density can be quantified to some extent using data obtained from automated electron backscatter diffraction scans over planar regions or volumes using the three-dimensional imaging techniques that are currently available. Reliable measurements require that the step size of the orientation data used in determination of geometrically necessary dislocation densities be on the scale of the microstructural information. Measurements were performed in deformed Cu, Al and steel specimens. Geometrically necessary dislocation density in Cu deformed 10% in compression was about 15–30% of the overall estimated dislocation density. Measurements in Al demonstrate that three-dimensional estimates are on the order of 1.2–2 times the values obtained from 2D measurements on the same structures. Analysis of interstitial free steel specimens shows an increase in average geometrically necessary dislocation density by an order of magnitude for specimens deformed to 12% tensile deformation elongation.

Local deformation heterogeneity in cyclically deformed interstitial free steel

“…In the present investigation, step size of EBSD scan was 1 μm. The estimated GND densities are of the same order as that reported by Field et al 21 for the same step size, but for monotonically deformed condition.…”

The orientation and strain dependence of dislocation structure evolution in monotonically deformed polycrystalline copper

“…This prohibits the observation of dislocation development process. The lowest GND density readily detected by conventional EBSD has been assessed by various authors (Adams and Kacher, 2010;Chekhonin et al, 2014;Field et al, 2012) and is step size dependent. In copper at a 0.5µm step size GND density below 10 14 m -2 cannot be determined using conventional EBSD (Adams and Kacher, 2010;Jiang et al, 2013b).…”

Evaluating Deformation-Induced Grain Orientation Change in a Polycrystal During In Situ Tensile Deformation using EBSD

“…For reference, averaged orientations for each original parent grain in the undeformed structure are given as large black dots in each IPF's. The contoured pole figures on the right side of Figure 8 reveal an expected trend toward an increasingly strong 〈110〉 texture [α-fiber texture commonly found in deformed BCC polycrystals (Raabe et al, 1994;Field et al, 2005;Engler & Randle, 2010)] as deformation progressed. As the tensile deformation progressed, the pixel measurements become more diffuse and by the third strain step (left side of Fig.…”