Molecular dynamics simulations of stress-induced phase transformations and grain nucleation at crack tips in Fe

The molecular dynamics simulation technique is used to study a stress-induced new grain formation mechanism at the crack tip of a nanocrystalline α-iron sample at temperatures ranging from 100 to 600 K. The stress-induced formation of new bcc grains, created inside existing grains, is found to occur through a metastable bcc to fcc phase transformation at the crack tip of the sample. A Nishiyama–Wassermann orientation relationship is found between the original bcc grain and the fcc phase and a Kurdjumov–Sachs orientation relationship is found between the new bcc grain created and the fcc transition phase. The new grain nucleation is observed to increase with increasing temperature and stacking faults associated with the fcc phase are observed at the higher temperatures.