Cyclic stress–strain response and surface deformation features of [011] multiple-slip-oriented copper single crystals

Abstract

Cyclic deformation behavior and surface deformation features of [011] multiple-slip-oriented single crystals were investigated at constant plastic shear strain amplitude ( γ pl) in the range of 1.1×10 −4–7.2×10 −3 at room temperature in air. It was revealed that the cyclic deformation characteristic of [011] copper single crystal is quite different from that of [001] and [ 111] multiple-slip-oriented copper single crystals. The [011] crystal exhibits a rather low initial hardening rate, which does not increase notably even under higher plastic strain amplitudes. The cyclic stress–strain (CSS) curve of the [011] crystal exhibits a clear plateau region over the range of plastic strain amplitude investigated. Surface observations indicated that the primary persistent slip bands (PSBs) already occur under a lower strain amplitude of 1.1×10 −4, but the operation of secondary slip was strongly suppressed by the corresponding dislocation interactions even at high strain amplitudes. This slip characteristic was suggested to be associated with the occurrence of the plateau region. When γ pl≥2.5×10 −3, two types of deformation bands (DBI and DBII) formed on the specimen surface and their habit planes are perpendicular to each other strictly. An analysis based on the classical crystallographic deformation geometry was proposed to interpret the existence of an irreversible rotation of crystal in single crystal subjected to symmetrical push–pull loading. This phenomenon is assumed to be an essential reason for the formation of DBI and DBII. When γ pl≥5.0×10 −3, another type of deformation 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 formation of DBIII, giving rise to the cyclic softening in the cyclically deformed [011] copper single crystals at high strain amplitudes ( γ pl≥5.0×10 −3).