In situ study of microstructure and strength of severely predeformed pure Cu in deformation at 573 K

Abstract

The influence of grain refinement on the strength of pure Cu at the elevated temperature of 573 K was studied in situ in a SEM. Thermomechanical processing by eight passes of equal channel angular pressing at ambient temperature and annealing at test temperature generates grains of size. During deformation in the SEM at a relative elongation rate of further grain coarsening occurs by discontinuous recrystallization in subsequent waves causing oscillations of flow stress. Cracks start to form at the boundaries, but partly become intragranular when boundaries move away. The relaxation of flow stress in the periods where the imposed elongation was interrupted yields information about the deformation kinetics. Two mechanisms are identified. One is thermally activated glide related with defect generation. The second one accompanies the processes of microstructure restoration. Under the present deformation conditions, the grain coarsening by DRX does not soften the material but leads to slight hardening as high-angle boundaries are exchanged for low-angle boundaries. This is discussed in terms of boundary-mediated processes.

Keywords:

• ECAP
• dynamic recovery
• static recrystallization
• dynamic recrystallization
• grains
• in situ observation
• strength
• stress relaxation

Notes

No potential conflict of interest was reported by the authors.

1 Normalization of the qs strength makes sense because for Cu with small hab-fraction the normalized qs strengths appear to be rather insensitive to the absolute values of [6,7].

Additional information

Funding

Financial support for this work was provided by the Czech Science Foundation [grant number P108/11/2260]; the Central European Institute of Technology with research infrastructure supported by the project number [CZ.1.05/1.1.00/02.0068] granted by the European Regional Development Fund.