Chemical order transitions within extended interfacial segregation zones in NbMoTaW

Abstract

Interfacial segregation and chemical short-range ordering influence the behavior of grain boundaries in complex concentrated alloys. In this study, we use atomistic modeling of a NbMoTaW refractory complex concentrated alloy to provide insight into the interplay between these two phenomena. Hybrid Monte Carlo and molecular dynamics simulations are performed on columnar grain models to identify equilibrium grain boundary structures. Our results reveal extended near-boundary segregation zones that are much larger than traditional segregation regions, which also exhibit chemical patterning that bridges the interfacial and grain interior regions. Furthermore, structural transitions pertaining to an A2-to-B2 transformation are observed within these extended segregation zones. Both grain size and temperature are found to significantly alter the widths of these regions. An analysis of chemical short-range order indicates that not all pairwise elemental interactions are affected by the presence of a grain boundary equally, as only a subset of elemental clustering types are more likely to reside near certain boundaries. The results emphasize the increased chemical complexity that is associated with near-boundary segregation zones and demonstrate the unique nature of interfacial segregation in complex concentrated alloys.

A machine learning framework for the prediction of grain boundary segregation in chemically complex environments

“…In the quaternary case (Nb 0.33 Ta 0.33 W 0.34 as base, Mo as solute), the inclusion of W atoms further pushes the distribution to left, resulting in a strong favorable segregation peak for Mo. For this RCCA, Ta-W interaction was identified to be attractive in the bulk and repulsive in the interface regions at room temperature [20], which aligns well with our observations here. In addition, Nb is more inclined to segregate to interfaces compared to W, which agrees with most available studies on the segregation behavior in NbMoTaW [4,5,70].…”

“…This behavior becomes more common with increased solute concentration due to exhaustion of energetically favorable interface sites. The room temperature simulations mitigate temperature-induced structural transitions, such as interfacial disordering [20], although reaching this equilibrium for multielement systems is challenging due to their slow kinetics [3]. Figure 6(b) shows the site occupancies for the same ternary system at room temperature, with solute concentrations adjusted in 10 at.% increments starting from 10 at.% concentration, and includes the corresponding site availability plot for reference.…”

“…The non-uniform distribution of segregation energies with such a network results in a complex pattern of site availability for segregation. Furthermore, prior investigations have demonstrated that in the transition regions from interfaces to bulk sites, the compositional variation is notably affected by the presence of interfaces [19,20], with distinct structural ordering preferences and extended segregation zones being observed. This last finding indicates that segregation behavior is not confined to the immediate interface but instead extends into adjacent zones, resulting in areas that do not exhibit characteristics typical of either pure interface or bulk behavior.…”

Tension–Compression Asymmetry of BCC NbMoTaW in High Entropy Alloy Nanowires

“…Molecular dynamics (MD) simulation is an effective means of characterizing the microstructure evolution at the atomic level, − which is a challenge and important supplement to experimental observation. However, to date, only a limited number of MD simulations have been conducted on NbMoTaW RHEAs, with the majority of studies primarily focused on the effects of chemical heterogeneity. − Further research is needed to comprehensively investigate the deformation mechanism of NbMoTaW RHEAs and its correlation with their mechanical properties.…”