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

在钛/二氧化钛系统中，螺旋位错和刃位错的精确计算构造将通过利用“嵌入”的多尺度原子方法来实现：一种技术，其中自洽的极化离子紧密结合模型控制位错的非线性应力“核心”中的原子能量，而键级势模型-其提供更快，但不太准确，模拟原子能的方法--控制核心之外的原子区域。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的各种类型的位错系统之间的相互作用。阐述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。紧束缚和键序势方法的实施所需的参数拟合将基于贝叶斯优化技术。这将加速拟合过程，并将模拟从纯钛介质扩展到合金介质。在分压环境中模拟合金系统将提供对氧如何相互作用和扩散进出材料的洞察。在合金/氧化物界面处位错的传播、相互作用和堆积的差异将被完成。合金钛和纯钛介质在裂纹形态、形成和敏感性上的区别将被绘制出来。由合金的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相关联。

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.