Critical role of L21 and L12 phase in deformation behaviors of additively manufactured FeCrNiAlTi alloy

Abstract

Precipitation hardening is a widely used strategy to enhance the strength of face-centered cubic (FCC) alloys, but it often comes at the expense of ductility. However, the precipitates may also influence the deformation behaviors of the FCC matrix, such as strain induced stacking faults and twins, which could potentially mitigate or eliminate the loss in ductility caused by the increase in strength. In this work, we fabricated an FeCrNiAlTi FCC alloy via laser additive manufacturing, in which high density incoherent L2₁ phase and coherent L1₂ phase were introduced at cell walls and within cells respectively. An excellent balance between strength and ductility was achieved at both ambient and cryogenic temperatures by controlling the precipitation of intermetallic phases. It was found that the high density precipitates not only provide substantial strengthening but also promote deformation-induced stacking faults (SFs) and twinning, thereby enhancing work hardening through the creation of strain heterogeneity. In-situ neutron diffraction results reveal that the lattice strain after the yielding of the alloy is the predominant factors governing the formation of SFs and twins. Numerical simulation results exhibit that the large interfacial misfit of the incoherent L2₁ phase with the FCC matrix significantly enhances the local strain. Additionally, the combination of larger size and greater spacing of the L1₂ phase increases the local strain. Both L2₁ phase and L1₂ phase contribute to the enlarged local strain heterogeneity, thereby enhancing the stacking fault probability and promoting the formation of nano SFs and twins. This study presents the critical role of precipitates in tailoring deformation behaviors, thereby providing a new insight for designing strong yet ductile FCC alloys via engineering high density precipitates.