Influence of dislocations and Cottrell atmospheres on pressure-induced transformations in single-crystalline iron

Several studies of pressure-induced phase transformation confirm the appearance of the metastable hexagonal close-packed phase of iron under high pressure. However, the interplay of line and plane defects in the parent material with the transformation process is still not well understood. The principle objective of this project is to understand and explain the role of twins, dislocations and Cottrell atmospheres in changing the crystalline iron structure under high pressure by using classical molecular dynamics simulation. Our results show that the embryos of hcp-Fe are firstly formed at twins under hydrostatic compression. At such conditions, the nucleation of the hcp phase is observed for single crystals containing an edge dislocation. We find that buckling of the dislocation can help to accelerate the transformation process. The crystal orientations between the initial bcc-Fe and hcp-Fe structure are (110)bcc || (0001)hcp. Additionally, the presence of Cottrell Atmospheres surrounding an edge dislocation in bcc iron retarded the development of the hcp phase.