Hardening and strain rate sensitivity in stage IV of deformation in fcc and bcc metals

The paper demonstrates the occurrence of deformation stage IV and stage V in Ni and alpha-Fe as representatives for f.c.c. and b.c.c. metals for low and high deformation temperatures. Thermal activation analysis shows a constant strain rate sensitivity (SRS) in stage IV. This reveals the hardening in stage IV to be of athermal nature regardless of deformation temperature and lattice type. Comparison of the thermal obstacle density as derived from evaluated activation volume, with total dislocation density from X-ray diffraction and electrical residual resistivity suggests that hardening and softening mechanisms operate in the cell walls and cell interiors, respectively. (C) 1997 Elsevier Science S.A.