Increasing the physical fidelity of meso- and continuum-scale methods simulating the physical behavior of engineering materials requires a profound understanding of the effects of microstructure and interfaces at the nanoscale. Atomistic molecular dynamics (MD) simulations bear the potential to delineate the interplay between thermal, mechanical, chemical, and microstructural aspects. This talk encompasses two cases where we applied MD to understand those effects for target materials under processing and service conditions.

Case 1: A high-energy laser beam deposition on a metallic film surface results in microstructure changes that invalidate the laser process parameters and influence how the laser beam interacts with the target material, costing numerous energy and time-consuming trial and error experiments. We address this challenge by simulating the laser irradiation and its effects on metallic thin films (e.g., Au, Cr) and thin film stacks using large-scale multi-physics MD coupled with two-temperature models. We applied experimentally validated material and laser parameters to ensure physically informed MD and later mesoscopic hydrodynamics (HD) simulations. To this end, our MD-HD yielded crucial nanomechanical insights underpinning the laser-induced microstructure changes (e.g., grain size distributions, defect evolution) for different temperatures and stresses in metallic thin films and the contribution of interfaces in thin film stacks.

Case 2: Titanium aluminide (TiAl) alloys possess an excellent combination of material properties at elevated temperatures, with application in aircraft turbine blades. Fully lamellar TiAl alloys exhibit a complex microstructure with hierarchical interfaces across the length scales, from colony interfaces (highest level) to single-lamellar interfaces (lowest level). To systematically incorporate the effects of interfaces besides bulk intermetallic phases, we conceptualized the microstructure-informed atomistic models (MIAMs) whose characteristic geometric parameters largely matched the experimentally observed TiAl microstructure. By carefully combining such MIAMs and thermo-mechanical conditions experienced in service, we unraveled the nanomechanical origin of various phenomena at elevated temperatures, namely interface separation behavior, strain rate sensitivity, stress-induced deformation, effects of alloying elements on strength and ductility at the nanoscale. 

In this way, large-scale MD revealed the driving mechanisms near the microstructure boundaries and interfaces that remain otherwise intractable, thus contributing towards bridging the gap between atomic and continuum-scale simulations.