Development Of FeMnCrNi(C) Medium Entropy Alloy And Study On Its Mechanical Properties

Unlike previous alloy system,high-entropy alloys(HEAs)have attracted wide attention due to excellent mechanical properties and good corrosion resistance.In order to improve yield strength of face-centered cubic(FCC)HEAs and decrease the cost of HEAs,researchers have made great efforts to this end.However,these challenges still limit their potential for large-scale applications in the field of structural materials.In this paper,by adjusting the composition,calculating the thermodynamic parameters and innovating the thermo-mechanical treatment process,the cost of high-entropy alloys was decreased and the mechanical properties are further improved.In this work,a novel Co-free Fe40Mn20Cr20Ni20 middle-entropy alloy(MEA)was purposively developed.Meanwhile,the effects of the microstructure of the MEA in this paper on mechanical properties were studied.The research results show that the Fe40Mn20Cr20Ni20 MEA developed in this paper is a single-phase FCC structure after homogenization.After 70%rolling after annealing at 923 K,it possess heterogeneous microstructure composed of deformed grains with high density dislocations and recrystallized grains with low-density dislocations.At 77K,the yield strength and ultimate tensile strength of the Fe40Mn20Cr20Ni20 MEA can reach up to about 1.2 GPa and 1.3 GPa,respectively,uniform elongation is about 22%.The substantial improvement in mechanical properties is mainly due to dislocation strengthening.At the same time,the activation of twins at low temperatures also plays an important role.For heterogeneous MEAs,this study provides a relatively accurate model to predict yield strength.This model will conducive to the prediction of yield strength of other alloys.In addition,by dissolving C atom into the above FeMnCrNi MEA,FeMnCrNi(C)MEA with the low cost and more excellent mechanical properties was obtained.The effect of C content on the microstructure and mechanical properties of(Fe40Mn20Cr20Ni20)100-xCx MEA was studied.The study found that when x=1.1%,the(Fe40Mn20Cr20Ni20)98.9C1.1 MEA still maintain a single-phase FCC structure after annealing,and exhibits excellent corrosion resistance.As the number of the carbon increases,the grain size decreases and the recrystallization temperature increasing continuously.Meanwhile,the yield strength and ultimate tensile strength of the(Fe40Mn20Cr20Ni20)100-xCx MEA were improved,at the sacrifice of the ductility.The improvement in mechanical properties is mainly due to the resistance of dissolving atoms,the grain boundaries,and carbides on dislocations glide.