Linear Strain Hardening of Nickel-Cobalt Solid Solutions at Large Strains

Abstract

The influence of composition on Stage III and linear (Stage IV) strain hardening in Ni-Co solid solutions has been investigated at large strains using torsion tests. Torsion tests using thin-walled Ni-Co tubes were performed at strain rates of 10-3 s-1 and 10-4 s-1 at 296 and 573 K. Typically, the torsion stress-strain curves show linear strain hardening (Stage II), followed by a regime of decreasing hardening rate (Stage III), and at larger strains, a second linear hardening regime, Stage IV. In Stage III, the strain hardening and dynamic recovery are affected by stacking fault energy (SFE) as expected. The rate of strain hardening in Stage IV is not significantly affected by SFE or grain size, although it is temperature dependent. However, the strain at which Stage IV begins, increases with decreasing SFE. Stacking fault energy was also found to influence the evolution of microstructure.