The interaction between dislocations and TiC precipitates during creep of 15-15Ti austenitic stainless steel by Small-Angle Neutron Scattering

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15-15Ti austenitic stainless steel has high-temperature creep resistance and irradiation stability due to dispersed TiC nanoprecipitates in the material. In this study, we employ Small-Angle Neutron Scattering (SANS), X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Electron Backscatter Diffraction (EBSD), and Neutron Diffraction to investigate the evolution of TiC nanoprecipitates and dislocation density during creep (at 625 ℃ and 350 MPa) and heat treatment at the same temperature. The results reveal that during creep, TiC precipitates undergo rapid nucleation and growth, followed by a steady-state phase, and then a second rapid growth phase until creep fracture, with the final average diameter remaining below 10 nm. In contrast, during heat treatment, TiC precipitates also nucleate and grow rapidly but subsequently stabilize at a smaller average size than those observed in creep samples. Notably, a significant reduction in dislocation density during the tertiary creep stage is evidenced by a sharp drop in SANS data in the high-Q range, corroborated by TEM and XRD. This reduction was not observed during heat treatment. The regrowth of TiC precipitates during creep is closely associated with dislocation density reduction. These findings demonstrate that TiC precipitate regrowth is intrinsically linked to dislocation annihilation during creep deformation. The applied creep strain promotes dislocation motion, while the high binding energy between Ti/C solutes and dislocations facilitates efficient solute transport via dislocation migration. When these solute-laden dislocations interact with existing TiC precipitates, they become pinned, creating localized regions of Ti and C supersaturation that drive precipitate regrowth.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.