Tailoring dislocation structure and constructing coherent Y₂Ti₂O₇ and Laves stacking faults in 9Cr ODS alloys: A multiple strategy to enhance the strength and ductility

Simultaneously enhancing strength and ductility poses a significant challenge in 9Cr oxide dispersion strengthened (ODS) ferritic-martensitic (F-M) alloys. In this work, we propose a novel strategy combining Al-Si co-alloying with direct addition of Y₂Ti₂O₇ nanoparticles (YTO NPs), and then employing one-step quenching without tempering heat treatment to simultaneously tailor dislocation structure and construct coherent YTO NPs as well as Laves phase stacking faults (SFs) in 9Cr ODS F-M alloys. Our study reveals that adjusting Al/Si content can optimize martensite volume fraction and aspect ratio, and YTO NPs can suppress dislocation nucleation within the martensitic plane through coherent interface. This synergy mechanism improves strength-ductility via optimizing dislocation density. During deformation, besides the conventional YTO-dislocation mechanism, YTO NPs can simultaneously pin dislocations in different slip systems. Remarkably, YTO NPs can also induce the dual formation of dislocation loops and dipoles, which will inhibit the formation of axial cracks. Moreover, the precipitation of ∼100 nm Laves phases in matrix (BCC) creates deformable zones that evolve into Laves SFs, ultimately improving strength-ductility synergy. 1.5Al1Si alloy (1.5 wt% Al and 1 wt% Si) aligns with the Kocks-Mecking model, where YTO NPs and Laves SFs simultaneously enhance dislocation storage capacity (θ₀) while Laves SFs suppressing dynamic recovery (K), consequently improving work hardening rate. Finally, 1.5Al1Si alloy exhibits up to 1.2 GPa ultimate tensile strength ( R _m) while maintaining 8.4 % of total extension at maximum force ( A _gt). This study proposes a new strategy to enhance the strength and ductility of ODS alloys.