| dc.description.abstract | Alien impurity elements favor to stay at the defects, e.g. stacking fault, grain boundary (GB) in host materials and thus influence many material properties. On basis of atomistic simulations, the present thesis puts a focus on the impurity effect of Mg and vacancy on the generalized planar fault energy of Al, trying to probe the twinnability and deformation behavior of Al-Mg alloys. It is found that both Mg and vacancy possess a segregation tendency towards the stacking fault of Al, which is known as the Suzuki segregation. Deformation twinning in Al-Mg alloys is established as being generally difficult, consistent with the rarely reported deformation twin in Al-Mg alloys even when subjected to various severe plastic deformation strategies.
As a second part of this thesis, we’ve investigated the Mg and Cu segregation behavior at S5 (210)[001] symmetrical tilt grain boundary (STGB) in Al. Both Mg and Cu are shown to have a large driving force to segregate to Al GBs. Mg solutes are predicted to weaken the strength of the STGB, contrary to the cohesion enhancing effect of Cu solutes on Al GBs.
A third part of the thesis concentrates on the segregation behavior of light elements (C, P, and As) at a set of Si GBs, aiming to gain in-depth fundamental understanding on the impurity-GB interactions, which is important for the multi-crystalline Si based nano-devices and solar cells. It is shown that the segregation of C, P and As at Σ3 {111} GB is energetically unfavorable. GB core sites with large lattice distortion are energetically preferential for P and C segregation. In contrast, GBs having deep levels in the bandgap of density of states show strikingly attractive strength for P and As segregation. | nb_NO |
