Non-isothermal aging tailors hierarchical heterostructures in an L-PBF (CoCrNi)94Al3Ti3 medium-entropy alloy for tunable strength-ductility responses

Laser powder bed fusion (L-PBF) inherently produces nonequilibrium microstructures, providing opportunities for post-build microstructural regulation in medium-entropy alloys (MEAs). Here, a (CoCrNi) 94 Al 3 Ti 3 MEA was subjected to non-isothermal aging (NIA) to regulate precipitation and partial recrystallization. NIA produces a multiscale heterogeneous architecture comprising non-recrystallized and partially recrystallized regions, retained cellular substructures, and region-dependent L1 2 precipitates. With increasing NIA temperature, the recrystallized fraction increases and the L1 2 precipitate populations become more developed, with spherical precipitates prevailing in non-recrystallized regions and particle-like and lamellar precipitates in partially recrystallized regions. The NIA-treated alloys exhibit yield strengths of 1075–1223 MPa, ultimate tensile strengths of 1301–1490 MPa, and elongations of 18.9–28.6%. Postmortem multiscale characterization reveals more distributed slip and dislocation accumulation with abundant SF-associated planar defects in NIA550, whereas NIA600 exhibits more localized deformation and more prevalent wavy, non-planar dislocation configurations. Quantitative strengthening analysis identifies precipitation strengthening as the largest contribution to the enhanced yield strength. These results demonstrate that NIA can regulate the L-PBF-derived nonequilibrium microstructure to achieve tunable strength–ductility responses in additively manufactured MEAs.