  Due to their remarkable mechanical and chemical properties, Ti-Al based
materials are attracting considerable interest in numerous fields of
engineering, such as automotive, aerospace, and defense. With their low
density, high strength, and resistance to corrosion and oxidation, these
intermetallic alloys and compound metal-metallic composites have found diverse
applications. The present study delves into the interfacial dynamics of these
Ti-Al systems, particularly focusing on the behavior of Ti and Al atoms in the
presence of TiAl$_3$ grain boundaries under experimental heat treatment
conditions. Using a combination of Molecular Dynamics and Markov State Model
analyses, we scrutinize the kinetic processes involved in the formation of
TiAl$_3$. The Molecular Dynamics simulation indicates that at the early stage
of heat treatment, the predominating process is the diffusion of Al atoms
towards the Ti surface through the TiAl$_3$ grain boundaries. The Markov State
Modeling identifies three distinct dynamic states of Al atoms within the Ti/Al
mixture that forms during the process, each exhibiting a unique spatial
distribution. Using transition timescales as a qualitative measure of the
rapidness of the dynamics, it is observed that the Al dynamics is significantly
less rapid near the Ti surface compared to the Al surface. Put together, the
results offer a comprehensive understanding of the interfacial dynamics and
reveals a three-stage diffusion mechanism. The process initiates with the
premelting of Al, proceeds with the prevalent diffusion of Al atoms towards the
Ti surface, and eventually ceases as the Ti concentration within the mixture
progressively increases. The insights gained from this study could contribute
significantly to the control and optimization of manufacturing processes for
these high-performing Ti-Al based materials.
