High-entropy approach starting from a corner of the phase diagram in designing high strength Fe–Mn–Co-based alloys with good tensile ductility

The alloys without a base component (also called high-entropy alloys) with good mechanical properties can be obtained not only by compositional optimization starting from the equiatomic mixture but by dilution of the base component (Fe) in a commercial industrial steel by another transition metal. Low density Fe–Mn–Al–C system alloys containing up to 30 mass% of Mn and up to 10 mass% of Al is an excellent base system for utilizing the latter approach. In this article, we present a Fe–Mn-Co–Al–C alloy with good tensile plasticity of 10% and an extremely high yield and ultimate strength values up to 1590 and 1650 MPa, respectively, treated only by standard technological operations: homogenization, hot and cold rolling and annealing. This is achieved by exploring the high-entropy approach forming a duplex-type solid-solution structure without dispersion strengthening with carbide precipitates. Mechanical strengthening is a result of solid-solution hardening and deformation strengthening upon the applied thermomechanical treatments. This approach also can be applied to other various alloys. Impact statement Constant scientifc and technological progress requires the creation of new structural materials with enhanced properties. In addition, the next generation of commercial aircrafts and vehicles requires materials with a higher specifc strength to meet fuel emission requirements. However, research on conventional metallic alloys has reached a saturation point, requiring the development of new scientifc ideas to ensure further progress in this area of materials science. A recent promising invention is related to high-entropy alloys: alloys without a main component. A typical group of high entropy alloys is an equiatomic mixture of several 3d transition metals. However, one can approach the equiatomic composition by starting with an existing alloy composition by diluting the base metal component with a related metal. We propose using a lightweight Fe-Mn-Al-C steel with high Mn and Al content as an excellent base system. High-entropy alloys containing cF4 and cI2/cP2 crystalline phases are obtained in this work by diluting the main component (Fe) in the industrial Fe–Mn–Al–C steel with another 3d transition metal (Co). One of the obtained alloys showed mechanical properties superior to those of the base alloy. This approach can also be applied to various other industrial alloys in the future. Graphic abstract