Hot deformation behaviour of sintered cobalt

Hot deformation of sintered cobalt during hot compression testing was investigated in the temperature range of 700-1000 degrees C and at strain rates ranging from 0.0005 to 0.1 s-1. Cobalt underwent considerable dynamic recrystallization (DRX) during hot deformation, with stress-strain flow curves exhibiting one or several peaks followed by significant flow softening and leading to a steady-state stress. Constitutive equations were used to derive the flow stress behaviour. A physically based model to describe the strain rate as a function of stress was suggested for temperatures ranging between 775 and 1000 degrees C. In this case, a creep exponent (n) of 5 indicated that the deformation mechanism was controlled by the glide and climb of dislocations. The activation energy coinciding with the one for self-diffusion of ferromagnetic cubic cobalt implied a diffusion-controlled mechanism and the presence of face-centered cubic (FCC) cobalt during deformation. Interestingly, the results at 700 degrees C could not be perfectly fitted to this model and exhibited a higher resistance to deformation. This revealed that the glide and climb deformation mode was close to the transition where glide mode was dominant, and thus mostly glide occurred at 700 degrees C, especially for the largest strain rates.

Automated summary

The hot deformation behavior of sintered cobalt was investigated under high temperature and compression testing conditions, revealing considerable dynamic recrystallization and a model to describe the flow stress behavior. The results indicated that the deformation mechanism of cobalt was mainly controlled by dislocation glide and climb, with slightly different characteristics exhibited at different temperatures.