Effect of Grain Size on Mechanical Properties and Deformation Mechanism of Nano-Polycrystalline Pure Ti Simulated by Molecular Dynamics

Nano- and microscale titanium and its alloys have potential applications in semiconductor-based micro-electromechanical systems due to their excellent mechanical properties. The uniaxial tensile mechanical properties and deformation mechanism of polycrystalline pure Ti with five different grain sizes measuring 6.74–19.69 nm were studied via molecular dynamics simulation using the embedded-atom potential function method. The Hall–Petch relationships and the critical grain size of the polycrystalline pure Ti are given. The dislocation migration of grain boundaries is the main deformation mechanism when the grain size exceeds 16.61 nm, which causes a direct Hall–Petch effect. When grain sizes are smaller than 16.61 nm, grain boundary sliding is the preferred deformation mechanism, which causes an inverse Hall–Petch effect. The polycrystalline pure Ti shows the highest tensile strength and average flow stress of 2.70 GPa and 2.15 GPa, respectively, at the 16.61 nm grain size, which is the critical grain size in the Hall–Petch relationships. The polycrystalline Ti is at its highest strength when its grain size ranges from 16 to 17 nm. The current research provides a theoretical basis for the use of pure titanium in emerging technologies at the nanoscale.