Designing high ductility TiAl alloys based on dislocation nucleation mechanism

SP Wang and DM Zhu and ZT Lu and XB Feng and WJ Li and PC Zhai and Y Chen and GD Li and ZX Qi and G Chen, ACTA MATERIALIA, 292, 121027 (2025).

DOI: 10.1016/j.actamat.2025.121027

The yield strength and ductility of nanoscale biphasic materials are governed by the critical resolved shear stress (CRSS) for dislocation nucleation. Polysynthetic twinned (PST) TiAl single crystals with alternating layers of gamma-TiAl and alpha(2)-Ti3Al exhibit high yield strength and ductility at room temperature. However, the relationship between its high performance and dislocation nucleation mechanism has not been clearly understood. In this work, we investigated the influence of the interfacial dislocations and the normal stress of slip plane on dislocation nucleation in the gamma-TiAl/alpha(2)-Ti3Al alloys via biaxial loading using molecular dynamics simulations. Three types of dislocations were observed in the initial yielding stage, including 111<112(over bar) twin dislocation and 111<1(over bar)01 superlattice dislocation for gamma-TiAl, 11(over bar)00<112(over bar)0> prismatic dislocation for alpha(2)-Ti3Al. The analysis for the yield conditions revealed that there is an approximate linear relation between the resolved shear stress and resolved normal stress for the three types of slip systems, which is consistent with the results of first principles. We proposed a design strategy for high ductility TiAl alloys based on this relationship, which involves introducing stress differences between the CRSS of two phases through pre-stressing. To verify the effectiveness of this strategy in practical applications, we applied pre-compression to the PST TiAl single crystal to introduce the difference in strength between the two phases, which led to crack uniformly occurring in gamma phase but limiting in alpha(2) phase, finally increasing the elongation of PST TiAl single crystal by about 300 %.

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