Effect Of Cu And Al Content On Microstructure And Properties Of FeCrMnAlCu High Entropy Alloy

The high-entropy alloys with multiple principal elements have unique microstructure and outstanding comprehensive properties,which have broader development potentials in structural materials and functions compared to the traditional alloys.The high-entropy alloys composed of metals such as Ti,Nb,Co and Ni have been widely studied.However,the alloys composed of the above elements are expensive,and the high cost has limited the large-scale applications of high-entropy alloys.To address this problem,five low-cost elements,Fe,Cr,Mn,Al,and Cu,are chosen as the raw materials in this paper,and the vacuum melting process is employed to prepare the high-entropy alloys.The high-entropy alloys with better performances are obtained by changing the atomic ratio between Al and Cu.The influences of changes in alloy element content on the microstructure and mechanical properties are analyzed using various devices,including XRD,SEM,EDS,TEM,electronic universal testing machine,microhardness tester,and abrasive wear testing machine.The main results of this study are as follows:（1）The effect of Cu content on the microstructure and mechanical properties of FeCrMnAlCu high-entropy alloy is investigated.The FeCrMnAlCu_x（x=0,0.5,1.0,1.5,2.0）high-entropy alloy has a typical dendritic microstructure,composed of the dendritic microstructure of BCC structure,the interdendritic microstructure of FCC structure,and the nanoscale precipitates with BCC structure precipitated within the dendrites.The dendrite zone contains abundant Fe and Cr,and the interdendritic zone is rich in Cu.Al and Mn elements are distributed between the dendrit ic and interdendritic microstructures.With the increase of Cu content,the proportion of dendrites in the alloy microstructure will decrease,while the proportion of the interdendrit zone increases;the size of the second-phase particles precipitated in the dendritic microstructure of BCC decreases,and the volume fraction increases.Under the influence of these factors,the compressive properties of the alloy present the trend of the increase first and then decrease.The compressive strength and yield strength reach the maximum when x=1.0,which are 1230.2 MPa and 960.5 MPa,respectively.The compression deformation rate of the alloy reached the maximum value of 20.68%when x=2.0.With the increase of Cu content,the FCC phase increases and the BCC phase decreases,and the strain lattice s of FCC and BCC phases change.Under the combined effect of these factors,the hardness of the alloy increas es first and then decreases,reaching a maximum value of 421.4 HV at x=0.5.At this point,the alloy also reaches its best friction performance,with a wear rate of 2.25×10^-5 mm³N^-1mm^-1 at the ambient temperature.The mechanical properties of the FeCrMnAlCux high-entropy alloy have reached the le vel of similar high-entropy alloy of Fe Co Ni Al Cu,but it is more cost effective.（2）The effects of Al and Cu contents on the microstructure,mechanical properties and tribological properties of FeCrMnAlCu high-entropy alloy and related action mechanism are studied.The results show that the Fe Cr Mn Al_yCu_（2-y）（y=1.3,1.4,1.5,1.6,1.7）high-entropy alloy is a single-phase solid solution with BCC structure,and the increase of y promotes the formation of the BCC phase.All five combinations of alloys are composed of the dendritic microstructures.With the increase of y content,the area of the dendritic zone increases,while that of the interdendritic zone decreases.Among them,the Cu element is concentrated in the interdendritic zone,and the increase of Al element redu ces the segregation of Cu element.The lattice distortion effect and precipitation strengthening effect of the Al element with larger atomic radius lead to the excellent mechanical and tribological properties of the high-entropy alloy.With the increase of y,the yield strength gradually increases,reaching a maximum value of 1092.31 MPa at y=1.5.When y=1.6and 1.7,the alloy is fractured before yielding.Moreover,with the increase of y,the compressive strength and deformation rate both show an overall d ownward trend,reaching their maximum values at y=1.3,which are 1517.84 MPa and 43.36%,respectively.At this point,the microhardness of Fe Cr Mn Al_1.7Cu_0.3 high-entropy alloy reaches a maximum value of 559.9 HV.The addition of Al element can significantly improve the tribological properties of the alloy,especially when y=1.6,the wear rate of Fe Cr Mn Al_1.6Cu_0.4 high-entropy alloy is the smallest at the ambient temperature,which is 4.70×10^-6 mm³ N^-1 mm^-1.The morphology of the wear marks shows a similar trend.With the increase of y,the wear mark surface of the alloy becomes smoother,changing from abrasive wear to adhesive wear and oxidation wear.