Omega Phase Formation in Ti-3wt.%Nb Alloy Induced by High-Pressure Torsion

Area of Science:

• Materials Science
• Metallurgy
• Physical Chemistry

Background:

• Severe plastic deformation (SPD) is known to induce significant microstructural changes, including grain refinement, strengthening, and phase transformations.
• High-pressure torsion (HPT) is a powerful SPD technique used to process materials at extreme conditions.
• Titanium-niobium (Ti-Nb) alloys are of interest due to their unique properties and potential applications.

Purpose of the Study:

• To investigate the fundamental mechanisms of alpha (α) to omega (ω) phase transformations induced by HPT in Ti-Nb-based alloys.
• To characterize the evolution of microstructure and phase transitions under HPT.
• To understand the influence of niobium (Nb) concentration on the α → ω phase transformation.

Main Methods:

• Ti-3wt.%Nb alloy was annealed at different temperatures to achieve varying initial niobium content.
• High-pressure torsion (HPT) was applied to induce severe plastic deformation.
• X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used for material characterization.

Main Results:

• A small initial amount of beta (β)-phase completely transformed into ω-phase during HPT.
• HPT processing resulted in significant grain refinement of the α-phase.
• Partial transformation of the α-phase into the ω-phase was observed, yielding two types of ω-phase with different compositions.
• The extent of α → ω transformation was inversely related to the Nb concentration in the α-Ti phase.

Conclusions:

• HPT processing effectively drives α → ω phase transformations in Ti-Nb alloys.
• The formation of two distinct ω-phases is attributed to their origins from the initial β-phase and the α-phase.
• Niobium concentration plays a critical role in controlling the α → ω phase transformation kinetics and extent during HPT.