Multi-variant γ lamellar evolution in γ-TiAl alloys

Abstract

The morphology of nanoscale γ lamellae strongly influences the mechanical properties of fully lamellar Ti-Al alloys; however, the coarsening mechanisms governing these nanostructures remain poorly understood. This work combines phase-field simulations and experiments to investigate the growth and coarsening of γ lamellae. It reveals multiple lamellar orientation-dependent coarsening mechanisms, including coalescence, Ostwald ripening, and internal interface migration. The simulated planar or step-like γ/γ interfaces agree well with the experimental observations. The competing effects between elastic energy and chemical driving force on the evolution kinetics of γ lamellae are quantitatively characterized. Elevated elastic energy suppresses coarsening and refines the lamellar structure, whereas a large chemical driving force accelerates precipitation, coarsening, and splitting. A four-stage kinetic sequence is identified for γ lamellar evolution: nucleation and growth, quasi-steady-state coarsening, splitting, and steady-state coarsening. These findings offer novel insights into the complex coarsening mechanisms and kinetic pathways of multi-variant γ lamellae in γ-TiAl alloys.