Role of true and pseudo twin boundary in high-temperature creep of y-TiAl alloy: Atomistic mechanism and mesoscale model

YQ Zhu and M Yi and ZH Zhang and WL Guo, ACTA MATERIALIA, 299, 121418 (2025).

DOI: 10.1016/j.actamat.2025.121418

Lightweight y-TiAl alloys are attractive for high-temperature creep- resistant applications. In lamellar y-TiAl alloy, y/y twin boundary (TB) is critical, but it has two types including true TB (TTB) and pseudo TB (PTB) and their contributions to creep performance are still elusive. Herein, we decipher the role and atomic mechanism of TTB and PTB in y-TiAl creep via atomistic simulations and propose an atomistically informed mesoscale creep model with parameters depicting the individual contribution from TTB and PTB. We find that in high-stress region, the inferior creep resistance of alloy with PTB is attributed to the plastic deformation caused by slip-PTB interactions with dislocations inclined to PTBs. In medium-stress region (MSR), alloy with TTB exhibits dislocation sliding along TTB plane and significant TTB migration due to the conjugate slip systems across TTB, whereas the asymmetric slip systems across PTB restrict dislocation motion and thus improve MSR creep performance. We then construct a mesoscale creep model that considers the Peierls-Nabarro stress arising from dislocation sliding during TTB migration, as well as the interfacial frictional resistance caused by the high interfacial energy of PTBs. The presence of TTB promotes higher effective stress due to dislocation sliding along TTB, thereby enhancing the stress-induced thermally activated deformation. In contrast, the high interfacial energy of PTB increases frictional resistance and suppresses thermal activation, leading to superior high- temperature MSR creep resistance. These findings should shed light on achieving y-TiAl alloys with enhanced high-temperature creep performance by TBs design.

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