Molecular Dynamics Simulation of Tensile Mechanical Properties and Deformation Mechanism of Oxygen-Containing Nano-Polycrystalline α-Ti

Titanium (Ti) has a strong sensitivity to oxygen atoms. Adding interstitial oxygen to pure Ti can greatly alter its mechanical behavior. Oxygen atoms increase strength and hardness while making Ti brittle. Therefore, controlling the oxygen content in Ti is extremely important. To better understand the influence of oxygen on the mechanical behavior of pure Ti, the plastic deformation behavior of nano-polycrystalline alpha-Ti with different interstitial oxygen content was studied. Molecular dynamic simulations were performed using the second nearest-neighbor modified embedded atom method and the charge equilibration (Q(eq)) method to investigate the effect of O content, tensile temperature, and strain rate on the tensile mechanical properties and deformation mechanism of nano-polycrystalline alpha-Ti. Results indicate that the yield stress of nano-polycrystalline a-Ti increases with the increase of interstitial O content. {10 (1) over bar0}<10<(1)over bar>2> deformation twin was observed when the O content is less than 0.3%, and twin growth was mediated by well-defined"zonal dislocations"at the twin boundary. Different activated slip systems were transformed and diversified when the O content is larger than 0.3%, that is, the prismatic, basal, and pyramidal <c + a> slip systems were simultaneously activated, and the dislocation type changed to edge dislocations. The plastic deformation of nano-polycrystalline a-Ti was mediated by dislocation and grain boundary. In addition, the mobility of the grain boundary increased significantly with the increase of tensile temperature and strain rate. The formation of new grains was accompanied by Ti-hcp -> Ti-bcc -> Ti-hcp phase transformation, which was due to the relative rotation of the grains. The number of new grains increased with the increase of strain rate. The current work reveals the mechanical properties and deformation mechanism of nano-polycrystalline alpha-Ti, which promotes the design, and development of Ti-based nano-structured alloys with superior mechanical properties.