CYCLIC STRESS-STRAIN RESPONSE AND SURFACE DEFORMATION FEATURES OF [011] MULTIPLE-SLIP-ORIENTED COPPER SINGLE-CRYSTALS

Cyclic deformation behavior and surface deformation features of [011] multiple-slip-oriented single crystals were investigated at constant p lastic shear strain amplitude (gamma(pl)) in the range of 1.1x10(-4)- 7.2 x 10(-3) at room temperature in air. It was revealed that the cycl ic deformation characteristic of [011] copper single crystal is quite different from that of [001] and [(1) over bar 11] multiple-slip-orien ted copper single crystals. The [011] crystal exhibits a rather low in itial hardening rate, which does not increase notably even under highe r plastic strain amplitudes. The cyclic stress-strain (CSS) curve of t he [011] crystal exhibit a clear plateau region over the range of plas tic strain amplitude investigated. Surface observations indicated that the primary persistent slip bands (PSBs) already occur under a lower strain amplitude of 1.1x10(-4), but the operation of secondary slip wa s strongly suppressed by the corresponding dislocation interactions ev en at high strain amplitudes. This slip characteristic was suggested t o be associated with the occurrence of the plateau region. When gamma( pl)greater than or equal to 2.5 x 10(-3), two types of deformation ban ds (DBI and DBII) formed on the specimen surface and their habit plane s are perpendicular to each other strictly. An analysis based on the c lassical crystallographic deformation geometry was proposed to interpr et the existence of an irreversible rotation of crystal in single crys tal subjected to symmetrical push-pull loading. This phenomenon is ass umed to be an essential reason for the formation of DBI and DBII. When gamma(pl)greater than or equal to 5.0 x 10(-3) another type of deform ation band (DBIII) was observed on the specimen surface and its habit plane is exactly (001) with the maximum shear stress acting on it. The favorable macroscopic state of stress may be responsible for the form ation of DBIII, giving rise to the cyclic softening in the cyclically deformed [011] copper single crystals at high strain amplitudes (y(pl) greater than or equal to 5.0 x 10(-3)). (C) 1998 Acta Metallurgica In c. Published by Elsevier Science Ltd. Ali rights reserved.