Creep Fracture of Copper Tricrystal along Grain Boundaries

Abstract

The major objective of the present study was to investigate the creep fracture process of a copper tricrystal having 〈110〉-tilt Σ3, 3, 9 grain boundaries. Creep tests at 0.81 T_M (T_M: melting temperature on the absolute temperature scale) under 4 MPa tensile stress were carried out for three samples prepared from the same tricrystal. Grain-boundary sliding occurred along only the Σ9 boundary, and the triple junction of the boundaries completely suppressed the sliding. The three samples were in different stages of creep deformation. Creep fracture was initiated by sliding-induced voids along the Σ9 boundary. Grain-boundary damage by the void formation developed into complete separation along the Σ9 boundary, and the Σ9 boundary crack induced surface grooves along one of the Σ3 boundaries, arranged almost perpendicular to the tensile axis. The crack propagation resulted in the final fracture of the tricrystal along the Σ9 and Σ3 boundaries. The formation of cavities in the Σ3 fracture surface suggested that the final fracture occurred in a ductile manner after the neighboring grains were partly separated along the Σ3 boundary.