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

Abstract

The major objective of the present study was to investigate the effect of the constraint of grain-boundary sliding and its accommodation at triple junctions on the creep fracture of tricrystals. Tricrystals of pure aluminum and copper having 〈110〉-tilt Σ3, 3, 9 boundaries were grown by the Bridgman method. Creep tests were carried out for tensile specimens in which the Σ9 boundary made an angle of 45° with the tensile axis at temperatures above 0.80 T_M, where T_M stands for the melting temperature on the absolute temperature scale. In both aluminum and copper tricrystals, dominant grain-boundary sliding occurred along the Σ9 boundary. The aluminum tricrystal fractured along a plane across grains, far separated from the triple junction. In contrast, the copper tricrystal fractured via a complete separation along the Σ9 boundary followed by a tear-off of the remaining portion. This difference is accounted for by the different local deformation behaviors around the triple junctions to release the stress concentration induced by the constraint of Σ9 sliding, e.g., grain-boundary sliding along the Σ3 boundary in aluminum and crack formation along the Σ9 boundary in copper.