Lattice-based multicomponent diffusion framework – LEMONADE

High temperature materials rely on tailored microstructures to achieve specific properties and durability in extreme environments. The project ambition is to gain a better understanding of the diffusion processes underlying microstructure transformations in multicomponent systems, including diffusion-deformation interactions, and to develop numerical simulation tools able to anticipate these transformations. This will be achieved through a multiscale, multiphysics modelling framework, whose development will be supported by innovative experimental work.
The model will describe the time evolution of metal systems containing composition gradients, as a result of diffusion and local thermodynamic and mechanical equilibria. The simulation of microstructural features (pores, phase domains) at the scale of a grain (~ 10 µm) will serve to study diffusion mechanisms and derive homogenization models used in the simulation of polycrystals (~ 100 µm). This approach will also include a dialogue between 1D and 3D formulations, where 1D is used to elaborate the base diffusion model and to simulate homogenized systems, while 3D allows support for spatially resolved microstructural features and multiaxial stress states.
Diffusion couple experiments will be conducted on model alloys of controlled microstructures. These will be designed with increasing degrees of complexity, with the aim of accompanying specific aspects of the diffusion model. Local deformation fields resulting from interdiffusion will be monitored using inert markers and digital image correlation techniques, so as to investigate the role of the microstructure in diffusion mechanisms. Diffusion couples will also be subjected to mechanical loading, effectively resulting in a creep test with a controlled composition gradient, allowing the effect of externally applied stress on diffusion to be characterized.
The combination of modelling and experimental work will provide a framework to better understand interdiffusion in complex systems, including diffusion-induced deformation and porosity. This effort will find its main application in the lifetime analysis of thin-walled structures and alloy-coating systems, thus contributing to the accelerated development of more performant materials and structures. On the long term, the methods proposed in LEMONADE will also contribute to a better integration of microstructural ageing in complex mechanical simulations.