Discovering atomic scale mechanisms of stress corrosion cracking in aerospace titanium alloys

Accurate computational construction of screw and edge dislocations, in a titanium/titanium dioxide system, will be achieved by utilising the multi-scale atomistic approach of "embedding": a technique whereby a self-consistent polarisable-ion tight binding model governs the energies of atoms in the non-linear stressed 'cores' of dislocations, while a bond order potential model- which provides a faster, but less accurate, approach to modelling atomic energies-governs the regions of atoms outside of the core. The effects of interstitial oxygen on the dynamics of dislocations, and interactions between dislocation systems of various types, between and within the two different mediums, will be studied. Enhanced stress fields, generated from dislocation pile up at the interface between Titanium Dioxide and Titanium, and its effect on surface crack formation, will be elucidated. Parameter fitting, necessary for the implementation of tight binding and bond order potential methods, will be based on Bayesian Optimisation techniques. This will result in an acceleration of the fitting procedure and expansion of the simulations from a pure titanium medium, to an alloyed medium. Simulations of the alloyed system in a partial pressure environment will provide insight into how oxygen interacts and diffuses in/out of the material. The difference of dislocation propagation, interaction and pile up at the alloy/oxide interface will be accomplished. Distinctions between alloyed and pure Titanium mediums on crack morphology, formation and susceptibility will be drawn. Certain dislocation distributions/systems resulting from the machining and preparation of alloys will be linked to enhanced plasticity and fracture.