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Atomistic Mechanisms of Binary Alloy Surface Segregation from Nanoseconds to Seconds Using Accelerated Dynamics
Richard B Garza1,2, Jiyoung Lee3,4, Mai H Nguyen3
1Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States.
Journal of Chemical Theory and Computation
|June 7, 2022
Summary
Transient surface segregation in CuNi alloys is revealed by multi-timescale simulations. This study quantifies segregation rates, crucial for understanding alloy corrosion and catalysis, bridging computational and experimental timescales.
Area of Science:
- Materials Science
- Computational Materials Science
- Surface Science
Background:
- Surface composition significantly impacts alloy properties like corrosion resistance and catalytic activity.
- Understanding transient surface segregation kinetics is vital for predicting alloy behavior.
- Current computational methods often struggle to capture the long timescales involved in segregation.
Purpose of the Study:
- To investigate the kinetics of transient surface segregation in CuNi (100) bimetallic alloy surfaces during annealing.
- To elucidate the role of vacancy diffusion in the surface separation process.
- To bridge the gap between computational and experimental timescales for surface segregation phenomena.
Main Methods:
- Atomistic simulations of CuNi (100) surfaces under vacuum annealing.
- Employment of multi-timescale methods: standard Molecular Dynamics (MD), parallel trajectory splicing (ParSplice), adaptive Kinetic Monte Carlo (AKMC), and Kinetic Monte Carlo (KMC).
- Sampling of early transient, intermediate, and equilibrium states from nanoseconds to seconds.
Main Results:
- All four methods captured rapid vacancy diffusion to the surface within tens of nanoseconds.
- Stochastic vacancy re-entry into the subsurface was observed on microsecond timescales using AKMC and KMC.
- Kinetic vacancy trapping on the surface was identified as a factor influencing segregation rates.
- Equilibrium composition profile estimated on the order of seconds using KMC.
Conclusions:
- Multi-timescale simulations effectively capture rare events crucial for understanding surface segregation kinetics.
- Vacancy dynamics, including trapping and re-entry, play a significant role in transient surface segregation.
- The study provides a computational framework for predicting alloy surface evolution on experimentally relevant timescales.
