Atomistic modeling of Σ3 twin grain boundary in alloy 800H

Grain boundary engineering (GBE) has become an important thermomechanical processing strategy to enhance the physical and mechanical properties of polycrystalline metals in microstructure design. Solute segregation at grain boundaries can alter the electronic and strain energy states of the lattice and can impact the mechanical behavior in materials such as dislocation activity and yield strength. The twin boundary is one special type of grain boundary and has been of particular interest because of its role in deformation processes. The present work investigates twin grain boundary segregation induced strengthening in alloy 800H at temperatures of 300 K and 1000 K using Molecular Dynamics and Monte Carlo simulations. The simulations predicted no segregation preference of solute atoms (Ni and Cr) at coherent grain boundaries, but a significant segregation tendency to incoherent grain boundaries at a higher temperature during the simulated time. Shockley partial dislocations were formed and associated with Cr clusters. Deformation twins were found to only nucleate at the incoherent grain boundary. This solute segregation at the incoherent grain boundary increases the stress required to activate such a dislocation nucleation process. These findings extend the current understanding of the yielding behavior in alloy 800H, and more importantly, shed light on using GBE strategies to produce high-performance polycrystalline metallic materials.