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

Area of Science:

• Materials Science
• Crystallography
• Mechanical Engineering

Background:

• Polycrystalline hexagonal close-packed titanium (hcp-Ti) exhibits limited plastic deformation at room temperature.
• Understanding phase transformations is crucial for enhancing titanium's mechanical properties.

Purpose of the Study:

• To elucidate the nucleation and growth mechanisms of face-centered cubic titanium (fcc-Ti) induced by room temperature rolling in hcp-Ti.
• To characterize the crystallographic orientation relationship between the parent hcp-Ti and the newly formed fcc-Ti phase.
• To identify the atomic-level mechanisms governing the phase transformation.

Main Methods:

• Utilized advanced transmission electron microscopy (TEM) for in-situ observation of microstructural evolution.
• Employed density functional theory (DFT) calculations to investigate atomic mechanisms and energy barriers.
• Combined experimental and computational approaches to analyze nucleation and growth processes.

Main Results:

• Identified a novel orientation relationship between hcp-Ti and fcc-Ti: 〈0001〉hcp||〈001〉fcc and .
• Revealed that fcc-Ti nucleation occurs via a pure-shuffle mechanism with a minimum stable thickness of three atomic layers.
• Demonstrated that fcc-Ti growth proceeds through shear-shuffle mechanisms (two-layer disconnections) or pure-shuffle mechanisms (four-layer disconnections).

Conclusions:

• Room temperature rolling induces a unique fcc-Ti phase in hcp-Ti through specific shuffle and shear mechanisms.
• The observed phase transformation provides an additional plastic deformation mode in titanium, comparable to twinning.
• This finding opens new avenues for designing titanium alloys with improved ductility and formability.