Investigating Plastic Anisotropy of Single and Two-Phase (α2-Ti3Al + γ-TiAl) PST-TiAl Through Computational Yield Surface Analysis

Abstract

The anisotropic mechanical behaviour of multi-phase TiAl alloys is intrinsically governed by the anisotropic crystal properties and morphology of their constituent phases, which control the initiation of local plasticity. To advance the understanding of macroscopic plastic anisotropy in multi-phase alloys, this study presents a comprehensive numerical investigation of a two-phase (α2-Ti3Al + γ-TiAl) lamellar TiAl alloy, with a focus on the evolution of plasticity across multiple structural scales. Utilizing the crystal plasticity finite element method (CPFEM), the influence of lamellar orientation (φ) and applied loading angles (θ) on plastic deformation and yield surface evolution was analysed in both the individual phases and in the combined two-phase system. The findings reveal that phase-specific anisotropy stems from the activation of distinct slip systems in the α2 and γ phases, with the activation closely tied to the type of loading (e.g., proportional biaxial loading) and the direction of the load path. Furthermore, the anisotropy of the two-phase system is significantly influenced by the alignment between the lamellar interface orientation and the load-path direction. Analysis with varying load-path directions across different stress planes clarifies how local deformation constraints within the embedded phases modulate slip system activation, leading to either the enhancement or suppression of specific deformation mechanisms. This, in turn, alters the overall yield behaviour of the material. Based on these simulation results, this study provides a detailed understanding of the internal constraints within embedded phases and their role in the evolution of plasticity. It elucidates how anisotropy develops under diverse loading conditions and underscores the importance of hierarchical plasticity in shaping the global anisotropic response of TiAl alloys.