Dynamic Phase Transformation Mechanisms in Ti48Al5Nb2Cr0.6Re0.1C Alloy With Heterogeneous Layered Microstructure

Introducing solid-state phase transformations into the design of heterogeneous structures is considered an effective strategy for simultaneously optimizing both microstructure and mechanical properties. This study investigates the thermodynamic and kinetic mechanisms of the γ → α transformation in Ti48Al5Nb2Cr0.6Re0.1C alloy under different deformation conditions and explores its correlation with the formation of a heterogeneous layered structure. Results show that the relative content of the α₂ phase increases from 6.50% to 9.26%, indicating the occurrence of the γ → α transformation. Under 1150°C and 0.005 s⁻¹ strain rate, dynamic recrystallization accelerates the formation of equiaxed structures with increasing strain. Under the 1250°C/60%/0.05 s⁻¹ condition, a structure consisting of alternating layers of γ dynamic recrystallization and shear bands is formed. From a thermodynamic perspective, the γ → α transformation is driven by a more negative Gibbs free energy difference (ΔG_γ→α) and the actual critical stress below the yield stress of the γ phase. From a kinetic perspective, under 1150°C and 0.005 s⁻¹ strain rate, the transformation involves the formation of nano-intermediate phases, interface step diffusion, and adjustments of interfacial dislocation. Under the 1250°C/60%/0.05 s⁻¹ condition, the transformation is promoted by the < 110 >_γ and < 111 >_γ textures with high shear stress within shear bands. First-principles calculations indicate that under different uniaxial compressive stress states, the α₂ phase exhibits a decreased bulk modulus and an increased shear modulus, leading to an increase in theoretical hardness. Fine-grain strengthening and dislocation strengthening introduced by the γ → α transformation and heterogeneous structure are crucial for the increase in hardness.