Mo Microalloyed High-entropy Alloy And Its Surface Gradient Treatment

High-entropy alloys are composed of five or more elements and have many excellent properties.Generally,the FCC structure high-entropy alloy has low yield strength,good plasticity,and poor strength.Generally,it can be strengthened by solid solution strengthening,fine grain strengthening,work hardening and second phase strengthening.In this paper,a high-entropy alloy with high plasticity Co30Cr25Fe15Ni15Mn15(elongation rate up to 68%and low yield strength of the only 232 MPa)is the research object It is proposed to improve the yield strength of the alloy through methods such as Mo alloying,rolling and sliding friction,and explore deformation mechanism and strengthening mechanism.This paper uses XRD,SEM,EBSD,TEM,microhardness tester,nanoindentation and electronic universal testing machine to analyze and test the microstructure and mechanical properties of(Co30Cr25Fe15Ni15Mn15)100-xMOx series high-entropy alloys,and study different rolling temperatures and sliding.The effect of friction parameters on the structure and properties of(Co30Cr25Fe15Ni15Mn15)100-xMox series high-entropy alloys,the conclusions are as follows:The as-cast Co30Cr25Fe15Ni15Mn15 alloy has a single-phase FCC structure,and its microstructure is a typical dendritic structure.With the decrease or addition of Mo content,the alloy still has a single-phase FCC crystal structure,and the dendritic structure has also been refined.(Co30Cr25Fe15Ni15Mn15)95Mo5 alloy has Mo and Mn compounds between the dendrites.The microhardness of(Co30Cr25Fe15Ni15Mn15)100-xMox alloy increases with the increase of Mo content.The yield strength and plasticity of the alloy first increase and then decrease with the addition of Mo.Among them,(Co30Cr25Fe15Ni15Mn15)97Mo3 alloy has the best comprehensive mechanical properties and yields.The strength is 260 MPa,the tensile strength is 585 MPa,and the plasticity is 76%.When the rolling volume is 80%at 1000 ℃ and 1100℃,(Co30Cr25Fe15Ni15Mn15)100-xMox alloy is a uniform equiaxed crystal structure of FCC crystal structure.Due to the large number of annealing twins produced in the hot rolling process,the alloy has a certain degree of good plasticity.With the increase of the rolling temperature,the average grain size of the rolled Co30Cr25Fe15Ni15Mn15 alloy increased from 8.2977 μm to 20.732 μm,the yield strength and tensile strength of the alloy decreased,and the plasticity increased;the average of the rolled(Co30Cr25Fe15Ni15Mn15)97Mo3 alloy The grain size increased from 4.6821 μm to 17.653 μm,the yield strength and tensile strength of the alloy decreased,and the plasticity increased.Among them,the rolled(Co30Cr25Fe15Ni15Mn15)97Mo3 alloy at 1100℃ has the best comprehensive mechanical properties,with a yield strength of 389 MPa,a tensile strength of 820 MPa,and a plasticity of 81%.After sliding friction treatment,the alloy crystal structure is still consistent with the rolled(Co30Cr25Fe15Ni15Mn15)97Mo3 high-entropy alloy,which is an FCC single-phase structure.After sliding friction,the tissues after different cycles and different load treatments are gradient changes,and the cross-sectional hardness presents a gradient distribution.Among them,when the load is 500 N and the number of cycles is 100 T,the(Co3oCr25Fe15Ni15Mn15)97M03 alloy has the best comprehensive mechanical properties.The depth of the deformation layer is about 400 μm,and the surface layer is less than 5 μm.The grain size is relatively high;the yield strength is 681 MPa,and the tensile strength is 873 MPa,the plasticity is 37%.