On the evaluation of dislocation densities in pure tantalum from EBSD orientation data

Abstract

We analyze measurements of dislocation densities carried out independently by several teams using three different methods on orientation maps obtained by Electron Back Scattered Diffraction on commercially pure tantalum samples in three different microstructural states. The characteristic aspects of these three methods: the Kernel average method, the Dillamore method and the determination of the lattice curvature-induced Nye’s tensor component fields are reviewed and their results are compared. One of the main features of the uncovered dislocation density distributions is their strong heterogeneity over the analyzed samples. Fluctuations in the dislocation densities, amounting to several times their base level and scaling as power-laws of their spatial frequency are observed along grain boundaries, and to a lesser degree along sub-grain boundaries. As a result of such scale invariance, defining an average dislocation density over a representative volume element is hardly possible, which leads to questioning the pertinence of such a notion. Field methods allowing to map the dislocation density distributions over the samples therefore appear to be mandatory.

A stored energy analysis of grains with shear texture orientations in Cu-Ni-Si and Fe-Ni alloys processed by high-pressure torsion

“…The effect of γSFE on the stored energy is also examined. It must be noted that the stored energy estimated in the present study arose from the GND dislocations since the KAM approach allows only an estimation of this type of dislocation [16,22]. Full details on the evolution of the texture and the microstructural parameters, such as grain size and grain boundary orientation distributions, of the HPT-processed Cu-2.5Ni-0.6Si and Fe-36Ni alloys were given in earlier reports [5,6] and therefore the present investigation was undertaken to provide a special emphasis on the stored energy and the shear texture component correlations.…”

Experimental measurement of dislocation density in metallic materials: A quantitative comparison between measurements techniques (XRD, R-ECCI, HR-EBSD, TEM)

“…where is the difference of rotation (with respect to the axes of the basis) between two ∆𝑤 𝑖 𝑤 𝑖 neighboring points separated spatially by in the j-th direction. Thus, it arises the GND densities ∆𝑥 𝑗 obtained by EBSD or HR-EBSD depend on the step size [52,53], which will be further discussed in this study.…”

Hydrogen Embrittlement as a Conspicuous Material Challenge─Comprehensive Review and Future Directions

“…To achieve this, field methods allowing to map the dislocation density distributions over a sample appear to be mandatory, while defining an average dislocation density over a representative volume element is hardly sufficient. 460 2.3.2.5. Defactant Concept.…”

“…Based on these findings, it may be possible to simulate H induced fracture with a single HELP mechanism by implementing a failure criterion based on critical dislocation density or misorientation in the cell walls. To achieve this, field methods allowing to map the dislocation density distributions over a sample appear to be mandatory, while defining an average dislocation density over a representative volume element is hardly sufficient …”