Direct observation of grain boundary dislocation climb in ion-irradiated gold bicrystals

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Abstract
Thin-film gold bicrystals containing (001) low-angle twist boundaries, with twist angles in the range θ = 7-14°, and high-angle twist boundaries, with θ ≃ 37°, were prepared by welding evaporated films together face-to-face. All the boundaries contained regular orthogonal arrays of intrinsic screw grain boundary dislocations (GBD's) as well as more randomly occurring extrinsic edge GBD's having Burgers vectors essentially perpendicular to the boundary. The speciments were irradiated on one face with 20 kev gold ions producing excess self-interstitial atoms which diffused to the extrinsic GBD's causing them to climb in the boundary. The extrinsic GBD climb, in turn, caused the boundaries to act as overall interstitial sinks. The climb motion was observed directly by transmission electron microscopy. The intrinsic screw GBD's in the high-angle boundaries (and probably also in the low-angle boundaries) remained unaffected during the process, but possibly they acted as short circuiting pipes which delivered interstitials to the extrinsic GBD's. It is concluded generally that both low-and high-angle boundaries may act as point defect sinks (sources) by means of the climb of GBD's having Burgers vectors with components normal to the boundary plane. This process is actually a from of internal crystal growth (dissolution) with the GBD's acting as ‘internal crystal ledges’.