Microstructure And Properties Of FeCoNi_1.5CuB_0.5Y_0.2 High-entropy Alloy Prepared By Microwave Sintering And Heat Treatment

The unique alloy design and significant high-entropy effect of high entropy alloy,make the high entropy solid solution alloy have potential application value in many properties.Face-centered cubic high-entropy alloys have attracted much attention owing to their excellent plastic and toughness,but its application in the field of high-end engineering materials is limited by low strength.Therefore,in this paper,FeCoNi_1.5CuB_0.5Y_0.2 high-entropy alloy with B and Y elements as strengthening elements is selected as the research object.The alloy powder is prepared by high-energy ball milling,then shaped by microwave sintering,and finally heat treated,aims to improve the comprehensive mechanical properties of high-entropy alloys by optimizing key preparation parameters and heat treatment methods.Through XRD,SEM,EDS,TEM,network vector analyzer,Vickers hardness tester,compression testing machine,nanoindentation and other tests,the following main research conclusions have been obtained:（1）Through the study of the influence of high-energy ball milling time on FeCoNi_1.5CuB_0.5Y_0.2 high-entropy alloy,the following conclusions can be drawn:at the ball milling speed of 300r/min,the alloying has been preliminarily done after the milling time of 20h,and the particle size Dv（90）corresponding to the cumulative particle size distribution reaching 90%is 44.70μm.When the milling time reaches 40h,the large particles are obviously refined,the Dv（90）is 28.72μm.And the solid solution effect between elements is better.When the ball milling time reaches 60h,the powder is further refined,and the proportion of the particle size below 1μm increases significantly,indicating that the alloy powder has been crushed and refined to a greater extent after a long time of ball milling.After further extending to 80h,the powder appeare welding phenomenon to form agglomerates,and part of the powder is contaminated by oxidation.Therefore,the optimized high-energy ball milling time is60h.（2）In order to study the absorbing performance of the powder under the best ball milling time,take the powder after high-energy ball milling for 60 hours and test it at2～18GHz.The result shows that the alloy powder has multiple dielectric properties and magnetic resonance peaks.At a matching thickness of 3.0mm,the reflection loss at a frequency of 8.23GHz is the lowest value-32.1d B.At the microwave sintering frequency of 2.45GHz,the reflection loss of the matching thickness of 4.5 mm is only-3.2d B,which requires a silicon carbide heating cavity to play an auxiliary heating role.（3）Through the investigation of the influence of microwave sintering temperature on FeCoNi_1.5CuB_0.5Y_0.2 high-entropy alloy,the following conclusions can be drawn:when the sintering temperature is 800℃,the phase analysis shows that the FCC phase and the intermetallic compound M₃B（M=Fe,Co,Ni）have been formed.As the sintering temperature increases,XRD analysis shows that Cuelement gradually dissolves into the main peak（111）_FCC and shifts to a small diffraction angle.When the sintering temperature reaches 850℃,the HCP phase comes to being.When the sintering temperature is increased to 950°C,the Cuelement is completely dissolved.When the sintering temperature reaches 1000℃,twinned YB₆ phases are also observed in the HCP phase.From the performance point of view,when the microwave sintering temperature is 950℃,the microhardness is 285HV and the compressive strength is1077.25MPa.When the temperature reaches 1000℃,the compactness reaches the maximum value of 92.33%,but the microhardness and compressive strength are reduced,while the compressive plasticity increases to the maximum value of 20.56%.（4）The effect of heat treatment on microwave sintered FeCoNi_1.5CuB_0.5Y_0.2 high-entropy alloy was studied,and the following conclusions can be drawn:with the increase of heat treatment temperature,（111）_FCC and（200）_FCC shift to a large diffraction angle direction.When the heat treatment temperature is 900℃,particulate phase precipitated in FCC phase grains,which is consistent with the precipitation of Cuelement in the XRD analysis.When the heat treatment temperature is 950℃,there is no obvious growth and phase transformation process in the structure morphology.When the heat treatment temperature reaches 1050℃,the crystal grains grow up significantly,and the agglomeration extent of element Y is higher.From the performance point of view,the compactness increases with the increase of heat treatment temperature,and the maximum compactness reaches 97.14%.The hardness of the specimen at the heat treatment temperature of 1050℃is 16HV lower than that of 950℃,but the compressive strength and compressive ductility are greatly increased,which are 1275.32MPa and 29.30%.The nanoindentation result shows that the nanohardness of the HCP phase is greatly increased to 9.24GPa when the heat treatment is 1050℃.