Segregation and Ordering of Light Interstitials (B, C, H, and N) in Cr-Ni Alloys: Implications for Grain Boundary Stability in Superalloy Design

Abstract: The segregation and ordering behavior of light interstitials (B, C, and N) in Cr30-Ni is examined, as these elements are critical for grain boundary stability and high-temperature mechanical performance in Ni-based superalloys. Using Monte Carlo simulations, we identify the chemical and structural preferences of these interstitials in both bulk and grain boundary (GB) environments, aligning with experimental segregation and precipitation trends. Boron strongly prefers GBs over the bulk, where it enhances GB cohesion and stabilizes the GB structure. Uniquely, boron induces a structural transformation at higher concentrations, hinting at the formation of serrated GBs where boron content is high, which improves high-temperature mechanical performance. Carbon and nitrogen form carbide and nitride motifs and exhibit limited GB solubility, reinforcing their precipitation tendencies. In support of ongoing hydrogen embrittlement mitigation strategies, we also examined hydrogen behavior. Hydrogen demonstrated chemical stability in the Cr-Ni GB zone, suggesting it may preferentially migrate inward along Cr- and Ni-rich GBs while avoiding Mo-enriched regions, further supporting Mo's role in mitigating embrittlement. These findings suggest that Mo-containing borides may serve as effective barriers against hydrogen-induced degradation by inhibiting H ingress and stabilizing GB cohesion. By elucidating the chemical and structural preferences of these light interstitials, this work provides a robust computational framework for guiding superalloy design toward improved high-temperature grain boundary stability, resistance to hydrogen embrittlement, and controlled chemical ordering.