Achieving superior yield strength for medium-entropy FeCoNiAl0.3 alloy through ultrasonically modulating nanoscale precipitates

Abstract

This study found that superior yield strength in ultrasonically solidified FeCoNiAl_0.3 alloy was achieved by inducing high volume fraction of nanoscale precipitates (NPs) without requiring heat treatment. Once ultrasound was applied during solidification, accompanied by the refinement of γ matrix, the radius and volume fraction of L1₂-structured NPs gradually increased from 1.86 nm and 15.91% to 8.91 nm and 65.22%. Molecular dynamics simulations showed that ultrasound enhanced Al-Ni cluster density in solidifying alloy through promoting Al-Ni ordered atomic pairs formation and accelerating atom diffusion in liquid phase. These numerous clusters increased NPs nucleation rate and further facilitated Ostwald ripening for NPs growth. Superior yield strength as high as 1105 MPa was achieved for FeCoNiAl_0.3 alloy, surpassing nearly all as-cast FCC-based M/HEAs and Ni-based alloys both strengthened by L1₂ precipitates. These NPs contributed an exceptional 830 MPa precipitation strengthening, exceeding those well-designed M/HEAs prepared through rolling and heat treatment.