Grain size and temperature dependent plastic deformation and strengthening mechanism of nano-crystalline tial alloy

BC Zhou and H Cao and ZY Rui and RC Feng, APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 131, 724 (2025).

DOI: 10.1007/s00339-025-08738-x

TiAl alloy has attracted abroad interests for decades because of its high specific strength and high modulus. However, the strength, especially high-temperature strength needs to be further improved in an increasingly demanding service environment. Surface nano-crystallization has been proved to be an effective route for improving the strength of a material. In this work, molecular dynamics (MD) simulations are applied to study the effect of grain size on the mechanical behaviors of nano- crystallized gamma-TiAl (NC-gamma-TiAl) alloy under room temperature and high temperatures. It's found that the yield stress decreases with the decreasing of grain size, exhibiting the so-called inverse Hall-Petch behavior, and the flow stress increases firstly and then decreases with the increase of grain size under room and high temperatures. At room temperature, all the intrinsic stacking faults and extrinsic stacking faults, associated with Shockley partial dislocations, and deformation twins contribute to the plasticity, and the deformation twinning and cross slip of partial dislocations can provide additional strengthening effects except for the grain boundary strengthening effect in nano- crystalline. When the temperature rises to 1000 K, only some intrinsic stacking faults and a large number of Frenkel defects are found, which should be responsible for the much lower high-temperature strength. The results obtained in this work should be helpful for understanding the underlying strengthening mechanism of NC-gamma-TiAl alloy under the aim of high temperature applications.

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