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All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Understanding Fundamental Mechanisms Behind Anomalous Segregation Behavior at Grain Boundaries during Diffusional Creep

Recent experimental studies in a nickel (Ni)-rhenium (Re) alloy demonstrated anisotropic elemental segregation around grain boundaries (GBs) while under tensile strain. Some GBs showed Re enrichment, while others showed Re depletion. We hypothesize that differing vacancy fluxes to GBs, caused by the anisotropic elastic stresses generated within the polycrystal, results in anisotropic creep-induced segregation (CIS) and grain growth. Using molecular dynamics simulations, we developed a mechanistic understanding of CIS and determined the contribution of elastic stresses and grain growth in Ni-Re alloys. We find that the stress state of the GB significantly changes the segregation energy profile for Re atoms, leading to significant Re redistribution. Further, as the GB migrates, the segregation/desegregation tendency of Re leads to bands of Re enrichment/depletion. Our results have important consequences for the quantitative predictions of diffusion creep and for the design of high-temperature creep-resistant Ni alloys.

36 - MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Re3Ni by Materials Project

Re3Ni is Magnesium-derived structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Re is bonded to eight equivalent Re and four equivalent Ni atoms to form ReRe8Ni4 cuboctahedra that share corners with four equivalent NiRe12 cuboctahedra, corners with fourteen equivalent ReRe8Ni4 cuboctahedra, edges with six equivalent NiRe12 cuboctahedra, edges with twelve equivalent ReRe8Ni4 cuboctahedra, faces with four equivalent NiRe12 cuboctahedra, and faces with sixteen equivalent ReRe8Ni4 cuboctahedra. There are a spread of Re–Re bond distances ranging from 2.69–2.72 Å. There are two shorter (2.69 Å) and two longer (2.71 Å) Re–Ni bond lengths. Ni is bonded to twelve equivalent Re atoms to form NiRe12 cuboctahedra that share corners with six equivalent NiRe12 cuboctahedra, corners with twelve equivalent ReRe8Ni4 cuboctahedra, edges with eighteen equivalent ReRe8Ni4 cuboctahedra, faces with eight equivalent NiRe12 cuboctahedra, and faces with twelve equivalent ReRe8Ni4 cuboctahedra.

36 MATERIALS SCIENCE↗