From High‐Entropy Alloys to High‐Entropy Steels

Abstract

Inspired by high-entropy alloys, we study the design of steels that are based on high configurational entropy for stabilizing a single-phase solid solution matrix. The focus is placed on the system Fe-Mn-Al-Si-C but we also present trends in the alloy system Fe-Mn-Al-C. Unlike in conventional high-entropy alloys, where five or more equiatomically proportioned components are used, we exploit the flat configurational entropy plateau in transition metal mixtures, stabilizing solid solutions also for lean, non-equiatomic compositions. This renders the high-entropy alloying concept, where none of the elements prevails, into a class of Fe-based materials which we refer to as high-entropy steels. A point that has received little attention in high-entropy alloys is the use of interstitial elements. Here, we address the role of C in face-centered cubic solid solution phases. High-entropy steels reveal excellent mechanical properties, namely, very high ductility and toughness; excellent high rate and low-temperature ductility; high strength of up to 1 GPa; up to 17% reduced mass density; and very high strain hardening. The microstructure stability can be tuned by adjusting the stacking fault energy. This enables to exploit deformation effects such as the TRIP, TWIP, or precipitation determined mechanisms.

Strain hardening in Fe–16Mn–10Al–0.86C–5Ni high specific strength steel

“…As a summary of the mechanical properties measured so far for high specific strength steels, Fig. 4c and d compare the tensile properties of our HSSS with that of Kim et al [27], as well as with the conventional FeeMneAleC based austenitic [5,11,24], duplex [20,25] and triplex [17,23,26] steels. As can be seen, the HSSS in the present study shows an outstanding combination of the specific yield strength (SYS) and uniform elongation, while exhibiting an acceptable combination of the yield strength-to-ultimate tensile strength (YS-to-UTS) ratio and the uniform elongation.…”

“…Strain hardening is a prerequisite for large uniform tensile ductility. However, the mechanism of strain hardening remains an open issue for most high strength steels [5,22,27], because they deform very heterogeneously due to their inhomogeneous microstructures. Even for an initial single-phase alloy, for instance TWIP and TRIP steels, deformation twins and martensite formation make the strain hardening behavior complex [20,22].…”

Three Strategies for the Design of Advanced High-Entropy Alloys

“…Overview diagram showing typical ranges of total elongation to fracture and ultimate tensile strength for a number of different classes of steels. Mechanical properties of reported high-entropy steels exceed that of many known steels [104].…”

“…They introduced more solutes to the Fe-Mn-C system and used the increased configurational entropy to stabilize a single-phase homogeneous FCC phase. Their results are quite pleasing-ultimate tensile strengths of up to 1000 MPa and tensile elongations reaching up to 100% were reported [104]. Compared to conventional steels, these high-entropy steels possess a remarkable combination of properties, which is shown in Figure 3.…”

“…Entropy enhancement of the solute has been conducted to develop various high-entropy steels and high-entropy cast iron. Raabe et al designed high entropy steels based on the Fe-Mn-Al-Si-C system [104]. They introduced more solutes to the Fe-Mn-C system and used the increased configurational entropy to stabilize a single-phase homogeneous FCC phase.…”