High-density nanoprecipitates and phase reversion via maraging enable ultrastrong yet strain-hardenable medium-entropy alloy

Abstract

Maraging steels, known for ultrahigh strength and good fracture toughness, derive their superior properties from lath martensite structure with high-density nanoprecipitates. In this work, we designed a novel Fe-based medium-entropy alloy with a chemical composition of Fe60Co25Ni10Mo5 in atomic% (at%) by utilizing the characteristics of the maraging steels. By a single-step aging of only 10 min at 650 ℃, the alloy showed microstructures consisting of a very high number density of (Fe, Co, Ni)7Mo6-type nanoprecipitates in lath martensite structure and reverted FCC phase, which led to ultrahigh yield strength higher than 2 GPa. Additionally, the alloy exhibited a high ultimate tensile strength of ∼2.2 GPa and uniform ductility of ∼6% by harnessing deformation-induced martensitic transformation of the reverted FCC to BCC martensite, which has hardly been exploited in conventional maraging steels. This work demonstrates a novel direction to produce strong and ductile materials by expanding the horizons of material design with the aid of high-entropy concept and overcoming the limits of conventional materials.