Ultrastrong lightweight compositionally complex steels via dual-nanoprecipitation

High-performance lightweight materials are urgently needed, given the pressing quest for weight reduction and

the associated energy savings and emission reduction. Here, by incorporating the multi–principal element feature

of compositionally complex alloys, we develop the concept of lightweight steels further and propose a new class

of compositionally complex steels (CCSs). This approach allows us to use the high solid solution strengthening

and shift the alloys’ compositions into previously unattainable phase regions where both nanosized shearable

-carbides and non-shearable B2 particles are simultaneously formed. The achievement of dual-nanoprecipitation

in our CCSs leads to materials with ultrahigh specific tensile strength (up to 260 MPa·cm3 g−1) and excellent tensile

elongation (13 to 38%), a combination outperforming all other high-strength high-entropy alloys and advanced

lightweight steels. Our concept of CCSs is thus useful for guiding the design of ultrastrong lightweight metallic

materials.

High Entropy and compositionally complex steels via dual-nanoprecipitation
Science Advances 2020 Ultrastrong lightw[...]
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The Development of High-Strength, Lightweight Complex Concentrated Steels (CCSs) via Dual-Nanoprecipitation

The pursuit of advanced lightweight materials with a superior strength-to-weight ratio has led to the recent development of a novel class of Complex Concentrated Steels (CCSs). While traditional Fe-Mn-Al-C lightweight alloys rely on the uniform formation of 2–10 nm κ-carbides via spinodal decomposition, this new class of CCSs—specifically the Fe-26Mn-16Al-5Ni-5C (at. %) alloy—utilizes a more sophisticated dual-nanoprecipitation mechanism. By precisely tuning the chemical composition, a hierarchical microstructure is triggered, characterized by a dense "backpack" topology consisting of both shearable κκ-carbides and non-shearable B2 phase precipitates.

The mechanical superiority of this architecture stems from the synergistic interaction between these two distinct phases. In this system, the carbon-rich κκ-carbides are susceptible to nanoscale shearing; however, the continuous flow of dislocations is interrupted by the presence of the incoherent, carbon-poor B2 particles. This topological arrangement prevents percolative dislocation flow through the shearable regions, effectively suppressing strain localization. Furthermore, as dislocations encounter and pile up against the non-shearable B2 precipitates, they generate significant long-range back stresses. This mechanism promotes sustained strain hardening, which stabilizes plastic deformation and accounts for the alloy's impressive ductility (13% to 38% elongation).

The macroscopic result of this nanoscale engineering is a material that achieves an exceptional combination of low mass density (6.6 g/cm36.6 g/cm3) and remarkably high specific tensile strength (up to 260 MPa⋅cm3g−1260 MPa⋅cm3g−1). Crucially, because these CCSs can be produced using conventional bulk metallurgical processes—including induction furnace casting, homogenization, and standard hot- and cold-rolling—this alloy concept provides a scalable and industrially viable pathway for the next generation of high-performance lightweight structural materials.

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