CYCLIC STRESS-STRAIN RESPONSE OF A COPPER TRICRYSTAL AND BICRYSTAL

摘要

Cyclic deformation was applied to a copper tricrystal (TC) as well as a bicrystal (BC) at constant axial plastic strain amplitude in the range of 1×10~(-4) ≤ ε_(pl) ≤ 4×10~(-3) . The initial cyclic hardening of TC was found to be similar to that of BC at low strain amplitudes. The cyclic hardening of TC is higher than that of BC at higher ε_(pl) and the distinction becomes pronounced with ε_(pl) increasing. The cyclic stress-strain (CSS) curve of TC is obviously higher than that of BC. Both curves show almost no plateau. The above mechanical behaviors are in accord with surface morphologies. Two effects of the grain boundary triple junction (TJ) on slip have been found : one is retardation to the primary slip at lower strain amplitudes, the other is the activation of multiple slip systems due to the internal stresses caused by the strain incompatibilities. Microcracks nucleated near TJ at higher ε_(pl).