Doctor of Philosophy, The Ohio State University, 2019, Materials Science and Engineering

Titanium (Ti) and its alloys have a wide range of applications in biomedical, automotive and aerospace industries due to their excellent strength to weight ratio and corrosion resistance. Alpha phase Ti has hexagonal closed packed (hcp) structure that shows anisotropic plastic deformation; 〈 a 〉 type slip on prism planes is the easiest to activate but cannot accommodate deformation along the 〈 c 〉 axis. The low temperature ductility of Ti is linked to twinning. Therefore, understanding the mechanisms behind the twin nucleation and growth in Ti alloys is important from both theoretical and industrial application points of view. To that end, the present study seeks a better understanding of the atomic scale processes involved in twin nucleation mechanisms and the effect of alpha-stabilizing solutes such as interstitial oxygen, substitutional aluminum and rare earth elements on twinning. Systematic molecular dynamics (MD) simulations are used to identify the underlying mechanism of twin nucleation from dislocation/grain boundary interactions. Density functional theory (DFT) simulations are employed to examine the effect of oxygen interstitials on the twinning behavior of Ti. A systematic framework has been developed to predict the diffusion of interstitial elements near the twin boundaries in hcp alloys. Next, uncertainty that arises from first-principles calculations in predicting diffusion coefficients are quantified. Finally, solute segregation to the twin boundaries as a new mechanism for dynamic strain aging (DSA) is investigated in Ti and other hcp alloys.

Committee: Maryam Ghazisaeidi (Advisor); Michael Mills (Committee Member); Wolfgang Windl (Committee Member) Subjects: Computer Science; Materials Science