New horizons in multi-physics phase field modelling (NEWPHASE2)

We have gained, through the years, a relatively good understanding of how materials and structures behave ‘on their own’, in the absence of interactions with the environment. However, when engineering components are exposed to aggressive environments, the problem becomes interdisciplinary (chemistry, mechanics, materials science) and much more difficult to understand and predict. As a result, catastrophic failures due to electro-chemo-mechanical material degradation phenomena such as corrosion are ubiquitous, even in the most developed countries with well-established engineering standards and protocols. Only in the UK, the annual cost of corrosion damage is estimated to be approximately £46 billion. NEWPHASE, the first stage of this UKRI Future Leaders Fellowship project, aimed at developing the first class of mechanistic models for chemo-mechanical material degradation challenges, from localised corrosion to battery degradation. The underlying hypothesis was that the combination of phase field modelling techniques, which make moving interfacial problems amenable to simulation, and coupled multi-physics models, which directly simulate the underlying electro-chemo-mechanical physical processes, would result in ‘fitting parameter’-free models with unprecedented predictive abilities. The project was arguably a success, and demonstrated on various chemo-mechanical problems, with a particular focus on corrosion and battery degradation, that multi-physics phase field modelling enabled predictions that relied purely on well-established physical constants, bringing a step change in predictive abilities, as demonstrated through benchmarking against laboratory experiments, full-scale engineering tests and blind, round-robin competitions such as the Purdue-SANDIA Damage Mechanics Challenge. However, the work also revealed new obstacles in this vision to establish physically-based, mechanistic material degradation models, and tackling these will be the objective of this second phase (NEWPHASE2).
A key challenge holding back a wider uptake of mechanistic, phase field-based coupled models is the difficulty of directly and independently measuring all the modelling inputs. While predictions are purely dependent on material properties, these are not always known or easy to measure (e.g., activation energies are known for some systems but not for others). This project will employ state-of-the-art electro-chemo-mechanical experiments to create a database for model materials (pure Fe, pure Ni) and technology-relevant alloys. Moreover, the work will enable ‘local’ validation of model predictions, increasing confidence and maximising uptake. In addition, the success of the combined phase field and multi-physics modelling paradigm will be extended to two areas where there is a pressing need for predictive, mechanistic models: delayed hydride cracking (DHC) and ammonia-induced material degradation. To this end, the electro-chemo-mechanical phase field-based hydrogen embrittlement models developed in the first stage will be taken to the next level, resolving the complexity of microstructural hydride formation and temperature/reaction-sensitive variations between hydrogen and anodic dissolution damage mechanisms, respectively. Given their importance on the structural integrity of nuclear infrastructure (DHC) and agriculture and shipping decarbonisation solutions (ammonia-induced damage), the work proposed is well-aligned with the vision postulated in the original proposal: to tackle chemo-mechanics structural integrity challenges holding back the energy transition. As in previous efforts, the aim is to provide mechanistic models that can be used to map safe regimes of operation, optimising and accelerating the deployment of new green technologies, and quickly and efficiently assess engineering solutions.