Cyclic deformation behavior of a copper tricrystal and bicrystal

Cyclic deformation was applied to a copper tricrystal (TC) as well as a bic rystal (BC) at constant axial plastic strain amplitude in the range of 1 x 10(-4) less than or equal to epsilon(pl) less than or equal to 4 x 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 B C at higher epsilon(pl) and the distinction becomes pronounced with epsilon (pl) increasing. The cyclic stress-strain (CSS) curve of TC is obviously hi gher than that of BC. No matter for TC and BC specimens, sigma(s) increases slowly with increasing epsilon(pl) and the difference between them is almo st independent of epsilon(pl) when epsilon(pl) < 1.5 x 10(-3), sigma(s) of TC and BC as well as the difference between them increase obviously after e psilon(pl) > 1.5 x 10(-3). Both curves show almost no plateau. The above me chanical behaviors are in accord with surface morphologies and simple analy sis. Two effects of the grain boundary triple junction (TJ) on slip have be en 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. Deformation bands appeared near grain boundary for BC at higher strain amplitudes while these did not occur for TC at the same strain amplitude. Microcracks nucleated near TJ f or epsilon(pl) greater than 0.7 x 10(-4). (C) 1999 Elsevier Science S.A. Al l rights reserved.