Plastic deformation-induced HCP-to-FCC phase transformation in submicron-scale pure titanium pillars

A novel phase transformation from hexagonal close packed (HCP) to face-centred cubic (FCC) was experimentally observed in the compression of pure Ti submicron pillars orientated along \( [11\overline{2} 0] \). The microstructural evolution in this work was systematically investigated using focused ion beam milling, nanoindentation with a flat tip, scanning electron microscopy, transmission electron microscopy (TEM), and high-resolution TEM. The experimental results confirm that the HCP-to-FCC phase transformation is attributed to the high strength induced by the size effect. Three variants of the FCC phase were observed in the deformed pillars, with an intersection angle of approximately 60° between the variants. The orientation relationships between the HCP matrix and FCC lamellas were determined to be \( \left\langle {002} \right\rangle_{\text{FCC}} //\left\langle {0001} \right\rangle_{\text{HCP}} {\text{and }}\left\{ {220} \right\}_{\text{FCC}} //\{ 10\overline{1} 0\}_{\text{HCP}} \). The deformation-induced phase transformation mechanism via consecutive slip of Shockley partial dislocations was proposed to interpret the formation of FCC-Ti.