Role of site-specific solute segregation and structural transition on grain boundary diffusion in Ni–Nb alloy

Abstract

The present work leverages atomistic simulation techniques to explore the influence of site-specific solute segregation and structural transition on grain boundary (GB) diffusion behavior in Ni–Nb alloys. In this regard, a hybrid Monte Carlo/molecular dynamics simulation method was employed to generate the equilibrium GB structure at various Ni–Nb alloy compositions (0.5, 1.0, 1.5, 2.0, 2.5, and 5.0 at. % Nb) and at different temperatures (1200, 1300, 1400, and 1500 K) to ensure thorough statistical sampling of atomic motion. The simulation results show that the GB diffusivities of solute (Nb) and solvent (Ni) atoms exhibit distinct composition/temperature dependencies. Further, the simulation results indicate that the diffusivity of Ni atom decreases in the Ni–0.5Nb specimen compared to the pure Ni at lower temperatures (1200 and 1300 K) due to preferential segregation of Nb atoms at the most favorable sites. Consequently, Nb atoms exhibit reluctance to migrate to other sites even under a driving force, and the overall diffusion process slows down. However, as the solute concentration and temperature increase, the GB structures become disordered, altering the GB diffusion mechanism. This study also analyses the effect of structure (GB volume), character (misorientation angle), and energy on the GB segregation and diffusion process across various ⟨100⟩ symmetric tilt GBs in pure Ni. The findings indicate that the GB structure, character, and energy significantly influence GB diffusion and GB segregation in bicrystal Ni GBs.