Anomalous strengthening in Fe-Cr-Ni-Al-Ti high entropy alloy via annealing-induced nanoprecipitate refinement

This study reveals an anomalous precipitate evolution mechanism regulated by annealing temperature in an Fe 61.5 Cr 17.5 Ni 12 Al 8 Ti 1 high-entropy alloy. We found that direct quenching after high-temperature annealing at 1273 K can induce a high density of nanoscale, coherent B2-NiAl precipitates (∼50 nm) within the BCC matrix, bypassing the conventional two-step process requiring separate low-temperature aging. The micro-mechanism involves dissolution of precipitates as annealing places the BCC matrix of the alloy in the BCC single-phase region, followed by non-equilibrium precipitation driven by high supersaturation during quenching. In contrast, annealing at 1073–1173 K retains the BCC matrix of the alloy in the BCC+B2 two-phase region, leading solely to precipitate coarsening. This temperature-dependent pathway bifurcation switches the dominant strengthening mechanism from Orowan bypassing to dislocation shearing, elevating the precipitation strengthening contribution to ∼546 MPa and ultimately increasing the alloy's yield strength remarkably to ∼1178 MPa.