TY - THES

T1 - On the reversibility of dislocation pile-ups at the micron scale: a µLaue diffraction study

AU - Kapp, Marlene

N1 - embargoed until null

PY - 2012

Y1 - 2012

N2 - Microbending tests on single crystalline and bicrystalline copper bending beams were performed to contribute to a further understanding of dislocation plasticity on the micron scale. The in situ µLaue technique was used to investigate the origin of the non-ideal elastic unloading behavior due to a plastic reverse deformation during unloading. Additional in situ scanning electron microscopy (SEM) experiments were performed using a Hysitron PicoIndenter with a high force resolution. Bending beams with three different conditions at the neutral axis were used. The first sample type was a single crystalline bending beam revealing plastic reverse deformation during unloading. The driving force for this reverse deformation is a backstress induced by a dislocation pile-up built during plastic deformation. The backstress causes the dissolution of the dislocation pile-up during unloading leading to the plastic reverse deformation. The µLaue data confirm the partial reduction of the geometrically necessary dislocation density during unloading, proving the dissolution of the dislocation pile-up. The second sample type was a bicrystalline bending beam, with the grain boundary aligned along the neutral axis. Contrary to the µLaue data, the SEM experiments showed an amplified plastic reverse deformation during unloading compared to the single crystalline bending beam. This is due to the strict confinement of the pile-up at the boundary, causing a higher backstress and a stronger dissolution of the dislocation pile-up. The third sample type was a single crystalline bending beam, where the neutral axis was removed. During loading a major amount of dislocations could escape to the inner bending beam surface. Consequently, only a small dislocation pile-up and backstress were formed, leading to an almost ideal elastic unloading behavior.

AB - Microbending tests on single crystalline and bicrystalline copper bending beams were performed to contribute to a further understanding of dislocation plasticity on the micron scale. The in situ µLaue technique was used to investigate the origin of the non-ideal elastic unloading behavior due to a plastic reverse deformation during unloading. Additional in situ scanning electron microscopy (SEM) experiments were performed using a Hysitron PicoIndenter with a high force resolution. Bending beams with three different conditions at the neutral axis were used. The first sample type was a single crystalline bending beam revealing plastic reverse deformation during unloading. The driving force for this reverse deformation is a backstress induced by a dislocation pile-up built during plastic deformation. The backstress causes the dissolution of the dislocation pile-up during unloading leading to the plastic reverse deformation. The µLaue data confirm the partial reduction of the geometrically necessary dislocation density during unloading, proving the dissolution of the dislocation pile-up. The second sample type was a bicrystalline bending beam, with the grain boundary aligned along the neutral axis. Contrary to the µLaue data, the SEM experiments showed an amplified plastic reverse deformation during unloading compared to the single crystalline bending beam. This is due to the strict confinement of the pile-up at the boundary, causing a higher backstress and a stronger dissolution of the dislocation pile-up. The third sample type was a single crystalline bending beam, where the neutral axis was removed. During loading a major amount of dislocations could escape to the inner bending beam surface. Consequently, only a small dislocation pile-up and backstress were formed, leading to an almost ideal elastic unloading behavior.

KW - Rückverformung

KW - Bauschinger Effekt

KW - Versetzungsaufstau

KW - Mikrobiegung

KW - Laue Mikrodiffraktion

KW - reverse deformation

KW - Bauschinger effect

KW - dislocation pile-up

KW - microbending

KW - Laue microdiffraction

M3 - Diploma Thesis

ER -