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

在钛/二氧化钛系统中，螺旋位错和边缘位错的精确计算构建将通过利用“嵌入”的多尺度原子方法实现：一种自一致的极化离子紧密结合模型控制位错非线性应力“核心”中的原子能量的技术，而键序势模型-提供了一种更快，但不太准确的原子能量建模方法-控制核心外的原子区域。将研究间隙氧对位错动力学的影响，以及两种不同介质之间和内部不同类型位错系统之间的相互作用。研究了二氧化钛与钛界面位错堆积产生的应力场增强及其对表面裂纹形成的影响。参数拟合是实现紧密绑定和键序势方法所必需的，将基于贝叶斯优化技术。这将导致拟合过程的加速，并将模拟从纯钛介质扩展到合金介质。在分压环境下合金系统的模拟将提供氧气如何相互作用和扩散进出材料的见解。在合金/氧化物界面处实现位错扩展、相互作用和堆积的差异。合金和纯钛介质在裂纹形态、形成和敏感性方面的区别将被绘制出来。由合金加工和制备产生的某些位错分布/系统将与增强的塑性和断裂有关。

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.