Core–shell architecture enables enhanced work-hardening capability and ductility in TiAl/Nb composites during hot compression deformation

Achieving robust high-temperature strength while retaining ductility is highly desirable for the engineering applications in the service temperature range of lightweight γ-TiAl intermetallics. We herein present a feasible strategy to achieve the above goals through core–shell architectural design. Based on the ductile β-Nb shell enclosing hard γ-TiAl matrix, annealing at 1200 °C for 1 h is primarily employed to promote Nb incorporation into γ-TiAl matrix, thereby lowering its stacking fault energy (SFE) while preserving a certain amount of ductile β-Nb phase. Consequently, the shell region includes chain-like β-Nb solid solution (β_ss), Nb-rich massive/lenticular γ-TiAl (γ_n) and basal B2, whereas the matrix region consists of lamellar γ/α₂ and equiaxed γ. Compared with the conventional counterpart γ-TiAl, the resulting multimodal microstructure exhibits both higher compressive strength of 2176 MPa and fracture strain of 49.3% during 650 °C compression. The superb strength–ductility combination is attributed to the markedly prolonged upturn stage of work-hardening rate, which arises from the hetero-deformation-induced strengthening (HDIS) effect at the vicinity of core/shell interface and twinning-induced plasticity (TWIP) effect in the γ_n and γ of the matrix colony. Thereinto, the multistage hardening process, involving twinning, twin intersection and stacking fault (SF) intersection, subdivides the equiaxed γ grain into hundreds of nanoscale subregions, responsible for the maximum deformability. Taking advantage of the inherent benefits of the core–shell architecture, enhancing the TWIP effect of the γ-TiAl matrix is crucial for realizing the strength–ductility synergy, inspiring new insights into optimizing the high-temperature performance of other structural materials.