CYCLIC PLASTICITY OF NICKEL SINGLE-CRYSTALS AT ELEVATED-TEMPERATURES

Single slip oriented nickel crystals have been cyclically deformed at deformation temperatures between 293 K and 900 K until saturation of t he stress amplitude. Persistent slip bands (PSBs) with a typical ladde r-like dislocation substructure occur at temperatures up to 800 K. Al 600 K and 750 K the measured cyclic stress-strain curves (CSSCs) exhib it extended ranges in which the saturation stress amplitude is nearly independent of the applied plastic strain amplitude. The plastic strai n amplitudes al the upper and the lower borders of these ''plateaus'' in the CSSCs decrease with increasing temperature. Most of the measure d structure lengths of the wall/channel arrangement in the PSB ladders and of the dipole arrangement in the PSB walls have been found to bec ome larger at elevated temperatures. The only exception observed is th e wall thickness which remains constant, independent of the temperatur e. Analysis of the measured data on the basis of current modelling app roaches shows that the local flow stresses and the residual stresses a re reduced at elevated temperatures. (C) 1997 Acta Metallurgica Inc.