Figure 4

Proposed mechanisms of FCC to HCP transformation. Schematic showing a change in the packing of the atomic layers from “ABC” (FCC) to “AB” (HCP) and the various possible nucleation sites for the transformation. (a) Propagation of a/6 \(\left\langle {112} \right\rangle\) Shockley partials transforming two layers of FCC to HCP. (b) Formation of SFT with ion irradiation and nucleation of a/6 \(\left\langle {112} \right\rangle\) Shockley partials on the SFT faces. Nucleation of a/2 \(\left\langle {110} \right\rangle\) dislocations at the (c) crystal-vacuum interface and (d) GB. This is followed by dissociation into a/6 \(\left\langle {112} \right\rangle\) Shockley partials and their propagation through the crystal with ion irradiation at 200 °C. (e) Nucleation of a/2 \(\left\langle {110} \right\rangle\) dislocations in the crystal matrix followed by dissociation into a/6 \(\left\langle {112} \right\rangle\) Shockley partials and their propagation through the crystal with ion irradiation at 200 °C.