High-pressure torsion of pure cobalt: hcp-fcc phase transformations and twinning during severe plastic deformation

• Published in: Applied physics letters 2013-05, Vol.102 (18)
• Main Authors: Edalati, Kaveh, Toh, Shoichi, Arita, Makoto, Watanabe, Masashi, Horita, Zenji
• Format: Article
• Language: English
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/1.4804273

Cobalt with low stacking fault energy in the forms of bulk and powders was severely deformed using high-pressure torsion to investigate the influence of grain size on allotropic phase transformations. A phase transformation occurred from metastable fcc to hcp until the average grain size reached the submicrometer level. However, an hcp → fcc phase transformation with nanotwin formation occurred together with the formation of a distorted hcp structure when the grain size was reduced well to the nanometer level (∼20 nm). Mechanical and magnetic properties were also investigated.