Dislocation nano-hydrides in nickel: Nucleation, evolution and effects on dislocation behaviors

FD León-Cázares and XW Zhou and C Alleman and CS Marchi, JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS, 205, 106310 (2025).

DOI: 10.1016/j.jmps.2025.106310

Nano-hydrides have been predicted to precipitate at the core of edge dislocations in the Ni-H system, a mechanism that may promote hydrogen embrittlement. However, nano-hydride nucleation, growth, and effects on dislocation behavior have seldom been explored. This work combines molecular dynamics grand canonical Monte Carlo (MD-GCMC) simulations and continuum modeling to uncover a wide range of phenomena linked to dislocation nano-hydrides. Simulations reveal that nano-hydrides can be stabilized at dislocation cores with all character angles, including screw segments, due to the hydrostatic stresses around the cores of the Shockley partials. Nano-hydride nucleation takes place in these regions, and growth is dictated by the character angle theta of the perfect dislocation. The equilibrium stacking fault width d(eq) varies dynamically to increase the local hydrostatic stress field and facilitate the formation of the nano-hydride, forming a constriction- like feature and leading to three distinct behaviors: d(eq) decreases for theta > 30 degrees, d(eq) remains unchanged for theta = 30 degrees, and d(eq) increases for theta <30 degrees. Remote hydrostatic and Escaig stresses are also shown to influence the nucleation stage, implying stress concentrations such as those ahead of crack tips may facilitate nano-hydride precipitation. Moreover, we identify a new hydrogen-induced 60 degrees dislocation reaction that emits a Shockley partial on a conjugate plane, with potential implications for twin nucleation. Testable predictions from this study are then used to reinterpret previous results from the literature. These findings provide a comprehensive framework to assess nano-hydride formation and evolution at dislocations in nickel and other face-centered cubic metals, with important implications to hydrogen embrittlement.

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