Abstract
The aim of this work is to present a quantitative analysis of features involved in recovery during annealing of deformed Tantalum. In pure metals where crystalline defects usually have high mobility, dislocation annihilation and rearrangement occur to a great extent prior to recrystallization. Therefore a complete understanding of recrystallization cannot be accomplished without an advanced knowledge of the recovery phenomenon. Depending on whether dislocations induce a measurable curvature in the crystal lattice or not, they are called Geometrically Necessary Dislocations (GNDs) or Statistically Stored Dislocations (SSDs) respectively. In the present work only GNDs are considered. For this purpose electron backscatter diffraction (EBSD) is an advantageous technique to obtain statistically representative results when compared to Transmission Electron Microscopy (TEM). However, a quantitative analysis of GNDs from EBSD data is not straightforward. Since local misorientations are induced by the curvature of the crystal lattice caused by GNDs, GNDs analysis can be done using local misorientations. However the values obtained from this analysis are step size dependent and influenced by the measurement noise. Reasoning on the basis that when the step size tends to zero, local misorientation should also tend to zero, measurement noise can be estimated [1]. The measurement noise appears to notably be very much dependent on the amplitude of local misorientations, which must be considered in the perspective of GND density calculation.
Highlights
When a crystalline material undergoes a plastic deformation, the crystalline lattice rearranges itself to compensate the geometric changes in the material, which in most cases introduces line defects called dislocations
(b) we can see that the maximal Geometrically Necessary Dislocations (GNDs) densities are around 1.5 1014 m-2 which is in the same order of magnitude of the critical value reported by Stüwe et al
The present work evaluates the advantage of applying Kamaya's method for estimating GND densities from electron backscatter diffraction (EBSD) maps, in the frame of a further research work dedicated to recovery in pure Tantalum
Summary
When a crystalline material undergoes a plastic deformation, the crystalline lattice rearranges itself to compensate the geometric changes in the material, which in most cases introduces line defects called dislocations. The average GND densities calculated using eq (1) with α=2 and KAM (considering the first, second or third neighbors) or using Kamaya's method are presented in table 1. From these values, the influence of the choice of the kernel radius without applying Kamaya's method is obvious. The result obtained with Kamaya's method is smaller than the one calculated with KAM This difference is mainly due to the measurement noise that leads to overestimating GND densities if not considered, and this is especially true when the crystal lattice is highly distorted due to a high. This parameter should be chosen carefully, in our case with 15° exclusion angle some grain boundaries was accounted for intragranular misorientation which tends to increase GND density
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