Thermal stability and corrosion resistance of ultrafine-grained high-entropy Fe30Ni30Mn30Cr10 alloy

Abstract

One of the promising research areas developing in recent times in the materials science is the development and research of high-entropy alloys containing several metal elements with the concentration close to equiatomic. The interest to them is generated by the fact that such alloys demonstrate the improved mechanical and functional properties. Another promising area improving strength of metallic materials is grain refinement using the severe plastic deformation methods. This work uses both approaches to form an ultrafine-grained (UFG) structure in the high-entropy Fe30Ni30Mn30Cr10 alloy. The paper presents the structure, strength, thermal stability, and corrosion resistance of a high-entropy alloy subjected to the high pressure torsion (HPT). The study of the structure carried out by scanning electron microscopy showed that the application of the HPT deformation leads to the formation of an UFG structure with an average grain diameter less than 200 nm depending on temperature of HPT processing. Microhardness measuring and tensile tests at room temperature showed that after grain refinement, an increase in microhardness and ultimate tensile strength occurs in a high-entropy alloy, which is more than three times higher compared to the initial coarse-grained sample. At the same time, the UFG samples of a high-entropy alloy manifested thermal stability of microhardness after annealing up to temperature of 500 °С. The electrochemical tests carried out in an aqueous solution of 3.5 % NaCl at the temperature of 37 °С demonstrated a high corrosion resistance of the UFG high-entropy alloy.