Rolling-induced Face Centered Cubic Titanium in Hexagonal Close Packed Titanium at Room Temperature

Abstract

Combining transmission electron microscopes and density functional theory calculations, we report the nucleation and growth mechanisms of room temperature rolling induced face-centered cubic titanium (fcc-Ti) in polycrystalline hexagonal close packed titanium (hcp-Ti). Fcc-Ti and hcp-Ti take the orientation relation: 〈0001〉hcp||〈001〉fcc and , different from the conventional one. The nucleation of fcc-Ti is accomplished via pure-shuffle mechanism with a minimum stable thickness of three atomic layers, and the growth via shear-shuffle mechanisms through gliding two-layer disconnections or pure-shuffle mechanisms through gliding four-layer disconnections. Such phase transformation offers an additional plastic deformation mode comparable to twinning.

An evaluation of the hexagonal close-packed to face-centered cubic phase transformation in a Ti-6Al-4V alloy during high-pressure torsion

“…It was reported that the α (hcp) to ω (hcp) and α (hcp) to fcc phase transformation can accommodate macro-strains comparable to compression twins in Ti [10] but it is important to note that an α (hcp) to ω (hcp) phase transformation was not observed in this research.…”

“…Basically, the formation of the fcc phase is not anticipated from the equilibrium phase diagram of Ti [4], but there are experiments showing an fcc structure in very thin epitaxial films [5,6] and in high-energy milled powders [7,8]. Very recently, an hcp to fcc phase transformation was reported in a bulk commercial purity α-Ti during cryogenic channel die compression [9] and cold rolling [10].…”

Disconnections and other defects associated with twin interfaces

“…An example of the drag effect is the formation energy, activation energy for motion, and general kinetics of kink nucleation and propagation at disconnections. Kinks and kink motion have been observed on disconnections [46,249]. However the 3D, non-periodic nature of kinks makes the calculation of their energetics difficult.…”

Dynamic Probing of Structural Evolution of Single Crystal Fe during Rolling Process Using Atomistic Simulation

“…In the present case, the surface mesh has been formed due to the occurrence of BCC to FCC phase transformation during the cryo‐rolling process (shown in Figure ). Literature studies have also shown the occurrence of phase transformation in various metallic systems during the rolling process, and it is to be noted that such transformations aid in the plastic deformation of the specimen at low temperatures. In the present case, it is observed that the BCC to FCC phase transformation occurs only near the roller‐specimen interface and as the specimen moves forward along the rolling direction (Figure c), the transformed region (FCC) regains its original BCC phase.…”