TY - JOUR
T1 - Resolving the geometrically necessary dislocation content in severely deformed aluminum by transmission Kikuchi diffraction
AU - Naghdy, Soroosh
AU - Verleysen, Patricia
AU - Petrov, Roumen
AU - Kestens, Leo
PY - 2018
Y1 - 2018
N2 - In this paper, severe plastic deformation (SPD) is applied to commercially pure aluminum. Monotonic high pressure torsion (HPT) processing is employed at room temperature, and the microstructure of samples deformed up to an equivalent strain of 50 is investigated by electron backscatter diffraction (EBSD). The distribution pattern and the density of geometrically necessary dislocations (GNDs) are evaluated by examination of transmission Kikuchi diffraction (TKD) maps. Three different methodologies are utilized for assessment of the GND density. It was observed that two distinct stages of grain fragmentation and steady-state occur during processing. During the first stage, a severe grain refinement was observed as the average grain size decreased from ~85 μm to ~1 μm at an equivalent strain of 10. Quantification of the density of dislocations in both deformation regimes showed that, independent of the choice of model, the GND density is greater in the fragmentation stage than in the steady-state stage. This observation was linked with the prevalence of the continuous dynamic recrystallization (CDRX) phenomenon in each stage. Furthermore, a significant presence of GNDs in the steady-state stage was characterized. Formation of microstructure, grain refinement and saturation of grain size are discussed in the light of statistics of GNDs.
AB - In this paper, severe plastic deformation (SPD) is applied to commercially pure aluminum. Monotonic high pressure torsion (HPT) processing is employed at room temperature, and the microstructure of samples deformed up to an equivalent strain of 50 is investigated by electron backscatter diffraction (EBSD). The distribution pattern and the density of geometrically necessary dislocations (GNDs) are evaluated by examination of transmission Kikuchi diffraction (TKD) maps. Three different methodologies are utilized for assessment of the GND density. It was observed that two distinct stages of grain fragmentation and steady-state occur during processing. During the first stage, a severe grain refinement was observed as the average grain size decreased from ~85 μm to ~1 μm at an equivalent strain of 10. Quantification of the density of dislocations in both deformation regimes showed that, independent of the choice of model, the GND density is greater in the fragmentation stage than in the steady-state stage. This observation was linked with the prevalence of the continuous dynamic recrystallization (CDRX) phenomenon in each stage. Furthermore, a significant presence of GNDs in the steady-state stage was characterized. Formation of microstructure, grain refinement and saturation of grain size are discussed in the light of statistics of GNDs.
KW - Aluminum
KW - Geometrically necessary dislocations (GNDs)
KW - Grain fragmentation
KW - High pressure torsion (HPT)
KW - Transmission Kikuchi diffraction (TKD)
UR - http://www.scopus.com/inward/record.url?scp=85045433706&partnerID=8YFLogxK
U2 - 10.1016/j.matchar.2018.04.013
DO - 10.1016/j.matchar.2018.04.013
M3 - Article
AN - SCOPUS:85045433706
SN - 1044-5803
VL - 140
SP - 225
EP - 232
JO - Materials Characterization
JF - Materials Characterization
ER -