Molecular dynamics study on the mechanical behavior and deformation mechanism of gradient oxygen content nano-polycrystalline α-T

Abstract

Interstitial oxygen significantly affects the mechanical properties of α-Titanium (α-Ti) by modifying dislocation slip and deformation twinning mechanisms. This study utilizes molecular dynamics simulations to investigate the influence of interstitial oxygen atoms on the tensile mechanical properties and deformation mechanisms of nano polycrystalline α-Ti, taking into account two distinct average grain sizes and varying gradients of oxygen content. The pinning effect of interstitial oxygen atoms on grain boundary relaxation dislocations is critical for stabilizing the nano-polycrystalline grain boundaries (GBs), with this effect becoming increasingly pronounced as the oxygen content rises. Additionally, the simulation results indicate that oxygen atoms at the twin boundary enhance the stability of the {10 $\bar{1}$ 2} twin boundary while exerting minimal influence on the migration of the {10$\bar{1}$ 1} twin boundary. The deformation associated with {10$\bar{1}$ 1} twinning leads to a crystallographic orientation transformation of the entire grain, which contrasts with the conventional grain rotation mechanism typically observed in nanocrystals. During plastic deformation, the primary dislocation slip mechanism is identified as the Shockley partial dislocation $\frac{1}{3}$ <$\bar{1}$ 100>, whereas the basal plane perfect dislocation $\frac{1}{3}$ <11$\bar{2}$ 0> easily dissociates into two Shockley partial dislocations due to the pinning effect of oxygen atoms. As a result, the dislocation density of the Shockley partial dislocation $\frac{1}{3}$ <$\bar{1}$ 100> is the highest.