A. Roatta

Electron backscatter diffraction study of orientation gradients at the grain boundaries of a polycrystalline steel sheet deformed along different loading paths

In a polycrystal, the heterogeneity of plastic deformation in a particular grain is greatly enhanced by adjacent grains that constrain the grains local behavior, often imposing orientation gradients. This work aims to characterize and quantify the local orientation gradients near grain boundaries (GBs). Electron backscatter diffraction (EBSD) measurements were made on a 0.67 mm thick aluminium-killed drawing quality (AKDQ) steel sheet subjected to different loading paths that are typical of forming operations. A statistical analysis shows that a considerable fraction of the analyzed GB profiles can be described by an orientation profile with a constant slope near the GB. In order to quantify this behavior, as well as the degree of localization, two new parameters, based on the local orientation gradient assessed by EBSD, are proposed: BET (boundary effective thickness) and GAS (gradient average severity). These parameters should be considered together, the BET as an effective thickness of the GB zone where the orientation gradient takes place and the GAS as a measure of the magnitude or severity of the orientation gradient. Additionally, the GAS parameter shows a strong correlation with the accumulated macroscopic strain for the investigated deformation levels and loading paths, while the BET profile clearly reveals the influence of the GB on the misorientation profiles. Tension and biaxial stretching results lead to a BET value between 1.5 and 2 µm. Finally, it is shown that the local misorientation in the GB zone, on both sides of the GB line, is disperse and it does not correlate simply with misorientation or even the slip-transfer geometry across the GB. Moreover, the observed average local misorientation dispersions in GB zones are different for each loading condition.

Simulation of Recrystallization Textures in fcc Materials Starting from Self-Consistent Modelling Results

Recrystallization (RX) textures in FCC materials have defied modelling for quite a long time despite the major micro-mechanisms influencing the texture development are currently considered understood. FCC materials are coarsely classified in high and low stacking fault energy materials with a rather continuous transition between them. Both extreme kinds will give rise, after rolling deformation and later RX, to what are called Cube and Brass texture patterns. Besides long discussions, not still settled, about the influence of twinning on deformation textures, attempts of simulating RX textures have been unsuccessful. The current contribution will show SelfConsistent (SC) plus RX modelling taking into account accumulated deformation energy and misorientation angles between neighbouring crystals. Starting from grains characterized by previous SelfConsistent simulations, nucleation is probabilistically allowed on each crystal whenever the accumulated energy is larger than certain threshold. Grain boundary mobility is commanded by a probability function of the misorientation angles also calculated by the SC model. The modelling is able to predict the right trend for many of the literature experimental data without resorting to other more sophisticated variables.