Development Of A Metastable Fe-based High-entropy Alloy And Study On Its Mechanical Properties

As the most potential alloy material in the new century,high-entropy alloys have attracted the interest of researchers from all over the world.At present,the research on high-entropy alloys is developing rapidly,and many high-entropy alloys with special properties have been developed.However,most of these high-performance high-entropy alloys contain typically alloying elements Co,V,etc.The aspect is essential since the expensive alloying elements used in HEAs have impeded their engineering applications.In order to meet the needs of practical applications,this article is dedicated to the development of low-cost,high-performance high-entropy alloys.In this paper,a metastable ferrous high-entropy alloy with a chemical composition of Fe₅₀Mn₂₀Cr₂₀Ni₁₀without Co is developed through phase diagram simulation,thermodynamic parameters and stacking fault energy calculation.And the relationship between alloy microstructure,mechanical properties and deformation mechanism is studied detailedly.The research results show that the ingot produced by vacuum induction melting has a single-phase face-centered cubic structure after being homogenized at 1200℃for 6 h.The crystal grains are completely equiaxed and the size is about 100μm.Then,under 298 K,the alloy exhibited excellent mechanical properties,with a yield strength of 300 MPa,a tensile strength of 550MPa,an total elongation of 60%,and a work hardening index of 0.41.The deformation mechanism by TEM analysis is the interaction between dislocation walls,dislocation cells and deformation twins.The Labusch model theory is used to accurately predict the yield strength of the alloy.Under 77 K,the alloy exhibits exceptional mechanical properties.As the temperature decreases,the stacking fault energy of the alloy decreases,it is easier to reach the critical stress value of martensitic transformation.Therefore,the alloy shows unique work hardening behavior.The interaction between dislocation,deformation twin,and dislocation-martensite is characterized by TEM,which further confirms that the occurrence ofεmartensite transformation has significant effect on the mechanical properties of Fe₅₀Mn₂₀Cr₂₀Ni₁₀HEA.Next,the single-phase FCC structure Fe₅₀Mn₂₀Cr₂₀Ni₁₀ high-entropy alloy is cold-rolled and annealed,that is,after 70%cold-rolled,it is annealed at 1073 K,1173 K,and 1273 K for1 h.Then,by means of TEM and SEM-EDS,the relationship among the evolution of the microstructure of the alloy,the change of mechanical properties and the inherent deformation mechanism was studied in detail.The research results show that the 1073 K,1173 K,1273 K samples after cold rolling and annealing treatment have precipitated Cr-rich intermetallic compoundσphase on the FCC structureγmatrix,showing the（FCC+σ）dual-phase microstructure.TEM characterization after tensile deformation shows that the intermetallic compoundσphase hardly deforms at room temperature 298 K,and only bears a part of the strain,and rare dislocations are accumulated at the phase interface.However,during the low temperature 77 K tensile deformation,theσphase has undergone severe shear deformation,and dense dislocation clusters accumulated inside it.Therefore,precipitation strengthening and back stress hardening caused by the existence of the hard second phase（σphase）can make the alloy possess excellent mechanical properties.