Dual precipitate simultaneous enhancement of tensile and fatigue strength in (FeCoNi)86Al7Ti7 high-entropy alloy fabricated using selective laser melting

Abstract

Recent studies have indicated that precipitation-strengthened high-entropy alloys (HEAs) show superior mechanical performance and have been successfully fabricated by additive manufacturing. However, the lack of fatigue and fracture research has limited the engineering applications of additive manufacturing HEAs. This work explored a dual precipitation-strengthened (FeCoNi)86Al7Ti7 HEA with excellent tensile and fatigue strength, prepared through selective laser melting and heat treatment. Compared with the as-built samples, the tensile properties and fatigue endurance limit improved through aging by 48.7% and 30%, respectively. The strengthening mechanism and enhanced fatigue performance were clarified in detail. The improvement in fatigue strength was attributed to the improved resistance of the L12 and L21 precipitates. During deformation, the dislocation shear coherent L12 precipitates reduced slip band energy and inhibited slip band expansion, while the L21 particles acted as obstructions for further slip band propagation, severely limiting the rapid formation and propagation of crack growth. In-situ TEM cyclic tensile-tensile testing also clarified the fatigue crack growth behavior, demonstrating that crack deflection due to L21 precipitate obstruction slowed down the crack growth rate and efficiently promoted the closure of the microcrack tips. This work offers implications for a new strategy to develop additive manufacturing HEAs.