Concerning the anomalous brittle fracture behaviour of iridium

Possible reasons for the anomalous “cleavage” fracture in face-centred-cubic (fcc) iridium are discussed. The detailed characteristics of fracture suggest that “cleavage” occurs by an alternate-slip/nano-void coalescence process, rather than by an atomically brittle process as is often assumed. The anomalous fracture behaviour (compared with fcc metals in general) is probably associated with unusual crack-tip surface structure and bonding characteristics rather than with some unusual bulk property.