Grain-Boundary Sliding and Its Accommodation at Triple Junctions in Aluminum and Copper Tricrystals

Abstract

The objective of the present study was to investigate the suppression of grain-boundary sliding and its accommodation at triple junctions. Tricrystals of pure aluminum and pure copper having ©110ª-tilt s = 3, 3, and 9 boundaries were grown. Creep tests were carried out at temperatures above 0.8T M , where T M is the melting point on the absolute temperature scale. In all specimens, boundary sliding occurred only in the 9 boundary. In aluminum tricrystals, sharp folds formed as a result of the suppression of 9 boundary sliding at the triple junction. Slip lines parallel to the trace of the (100) plane were observed in the fold. In copper tricrystals, no fold formed but a wedge crack was initiated at the triple junction and extended along one of the 3 boundaries aligned perpendicularly to the tensile axis. These results suggest that the ease or difficulty of fold formation affects crack formation during creep. [

Creep Fracture of Aluminum and Copper Tricrystals Having 〈110〉-Tilt Σ3, 3, 9 Grain Boundaries

“…We can recognize cracks along the 3 boundaries. As described in the previous paper, 10) short cracks were formed from the triple junction along the 3 boundaries. However, the cracks were shallow and did not penetrate through the specimen thickness and therefore had little effect on the final fracture of the specimen.…”

“…Multiple folds parallel to the 9 boundary are also observed. The tops of the folds are on an extension of In a previous study, 10) a sharp fold from the triple junction formed since the 9 boundary sliding was accommodated at the triple junction. Hence multiple folds formed in the present specimen due to the migration of the 9 boundary, which may have been induced by creep deformation.…”

“…The temperature and stress of creep tests were the same as those in the previous study. 10) They correspond to "transgranular creep fracture" (Al tricrystals) and "intergranular creep fracture" (Cu tricrystals) in the fracture mechanism maps. 21) The procedures of cross-sectional observation are schematically shown in Fig.…”

“…They showed that the suppression of grain-boundary sliding at the triple junction was accommodated by the formation of socalled folds, which were characterized as local slip bands activated on {111} or {100} planes. Recently, Okada et al 10) studied the creep deformation of Cu tricrystals of the same orientation. In the Cu tricrystals, due to the absence of slip on {100} planes, no fold formation was observed.…”