Exploring the effect of Cr and Mn on the intrinsic strength of the tensile properties of FeCoNi, FeCoNiMn, FeCoNiCr, and FeCoNiCrMn multi-principal element alloys using in-situ EBSD

As the composition elements in multi-principal element alloys increase, it can bring excellent mechanical properties. However, the strengthening mechanism of the additional element is still unclear. In this work, we establish a method based on the in-situ EBSD technology to explore the possible effect of additional elements on the intrinsic strength of tensile properties. We prepared four different multi-principal element alloys, including FeCoNi, FeCoNiMn, FeCoNiCr, and FeCoNiCrMn with similar initial status. We systematically investigated the evolution of the microstructure, dislocation density, twin boundary, grain size, and element distribution during the tensile process by in-situ EBSD and EDS. By carefully analyzing the results of four different multi-principal element alloys, the strength effects of the solid-solution hardening, grain-boundary hardening, twin boundary hardening, precipitate hardening, and dislocation hardening were peeled. The effect of the Cr and Mn element addition on the intrinsic strength can be explored. It is found that the element addition indeed increases the intrinsic strength from quaternary to quinary but not very clear from ternary to quaternary no matter Cr or Mn, which indicated that the intrinsic strength was more related to the number of elements in the alloy than to which element was present. This can be explained using the mixing entropy theory, which states that the intrinsic strength is enhanced when the mixing entropy is over a threshold between the MEA and HEA. This paper presents a method to study the individual factors affecting the tensile properties, which can help other researchers to better investigate HEA.