High-resolution electron backscatter diffraction: An emerging tool for studying local deformation

Abstract

Electron backscatter diffraction (EBSD) is a widely available and relatively easy-touse scanning-electron-microscopy-based diffraction technique. Recently, Wilkinson, Meaden, and Dingley presented two papers on a new cross-correlation-based analysis of EBSD patterns which allow variations in the elastic strain and lattice rotation tensors to be measured at a sensitivity of about 10 24 at high spatial resolution. This paper briefly describes the basis of the technique and how the resulting lattice curvatures can be used to estimate the geometrically necessary dislocation (GND) content in a sample. To illustrate the utility of the method for microscale deformation studies the following examples are described: first, nanoindentation near a grain boundary in a-Ti; second, transformation-induced GNDs in a dual-phase steel; third, thermally-induced and mechanically-induced deformation near carbides in a superalloy; fourth, GND accumulation during fatigue of a polycrystalline Ti-6Al-4V alloy.

Comparison of the dislocation density obtained by HR-EBSD and X-ray profile analysis

“…[4][5][6][7] It is the aim of the present work to explore the relevance and potential of the electron backscatter diffraction (EBSD) method based on the statistical properties of the local stress distribution determined by high-resolution electron backscatter diffraction (HR-EBSD). 8 To address their physical significance, the results will be compared to the outcome of discrete dislocation dynamics simulations and X-ray diffraction (XRD) line profile analysis, 9 a well established experimental technique for characterising dislocation structures. The detailed analysis of the peak shape allows determining major microstructural parameters, such as the coherent domain size, the dislocation density and its fluctuation.…”

“…HR-EBSD is a scanning electron microscope (SEM) based method, which allows determining the stress/strain in a crystalline material at the length scale of tens of nanometers. It is based on a cross-correlation method 8,[14][15][16][17][18][19] exploiting small changes in the backscattered Kikuchi diffraction patterns corresponding to a reference point and the actual point analysed. A detailed description of the technique can be found in Refs.…”

Microstructural damage evolution in two Ni based superalloys subjected to different mechanical loading conditions through quantitative EBSD measurements using Cross-Court software

“…As suggested in [11,13] the quality of the maps has been checked by looking at the values for the mean angular error (MAE) and the geometric mean of XCF (cross-correlation function) peak height (PH), and thresholds of PH>0.2 and MAE<0.008 rad values have been selected [13]. It was not possible to apply these thresholds to all the observations from all the maps, in particular for ex-service materials, but the MAE and PH maps have been used to provide the basis of comments on the results.…”

“…However it was not possible for the analysed testpieces as the mapped regions were inside the gauge lengths of the mechanically tested samples. Even when the reference pattern comes from a region with unknown strain, important information (lattice curvatures and elastic strain gradients) can still be determined and used to recover the GND (geometrically necessary dislocation) density distribution [11]. The GND density has been evaluated utilising the analysis given by Nye [12] and the assumptions for FCC crystals made by J. Jiang et al [13] have been here considered.…”

“…With respect to already published studies on structural materials [11,15,16] the approach defined here is relatively coarse, but extended to a huge number of specimens tested in different conditions. Importantly, it allows in an industrial organisation to develop further knowledge on material damage evolution and to assess a tool that can be applied to evaluate material condition on ex-service components.…”