Al4C3 growth mechanism based on diffusion of carbon atoms: First-principles study

The growth of aluminum carbide (Al4C3) plays a crucial role in the mechanical properties of carbon-reinforced aluminum composites; however, most of the studies focus on the direct observation of Al4C3, and its controlling mechanism is unclear. Herein, carbon transport in Al4C3 is investigated to clarify the growth mechanism using density functional theory (DFT) calculations. Five basic jump pathways of carbon are considered based on vacancy-mediated diffusion, which is sufficient to simulate possible models. A migration barrier for each site of carbon vacancy is calculated based on the jump pathways. Then, the transition state theory is used to quantify the diffusivity of carbon atoms by calculating the migration barrier. Additionally, the self-diffusion coefficients of carbon are calculated to investigate atomically-resolved transport mechanisms. The predicted effective migration barriers are in good agreement with the experimental results. The basal diffusivity is 3-4 orders of magnitude higher than the c-axis diffusivity. One should note that such a diffusion also exhibits strong anisotropy, which is consistent with experimental results. Finally, a growth model is built based on five basic jump pathways, which can explain Al4C3 growth both qualitatively and quantitatively.