Structure And Mechanical Properties Of CoCrFeNiCu High-entropy Alloys

This work mainly investigated and clarified that the effects of transitional Cuelements, low melting point Sn element and high melting point Nb element on thestructures and properties of CoCrFeNiCu high-entropy alloys. The research content andresults are as follows:The microstructures, compressive properties and microhardness of CoCrFeNiCuxalloys were investigated by changing the content of Cu element. The results showed that,CoCrFeNi alloy is composed of single FCC solid solution. A new rich-Cu FCC(FCC2)solid solution forms due to part of Cu element is segregated, therefore CoCrFeNiCuxalloys are composed of FCC1and FCC2solid solution with the addition of Cu element.The rich-Cu FCC2solid solution precipitates at grain boundary of CoCrFeNiCuxalloyswhen Cu contents are0.5and1.0mol. CoCrFeNiCuxalloys presents typical dendritesand rich-Cu FCC2solid solution precipitates in interdendritic zones when Cu content ismore than1.0. The yielding strength and microhardness of CoCrFeNiCu0.5alloy reachesthe maximum value of328MPa and162HV. With the Cu content increased, the yieldingstrength and microhardness of CoCrFeNiCuxalloys slightly decreased. CoCrFeNiCuxalloys exhibit excellent compressive deformation properties and without fracture after25%deformation at1×10-4s-1strain rate.Based on the above, the effects of Sn element with large atom radius and lowmelting point on the microstructures, compressive properties and microhardness ofCoCrFeNiCu2Snxalloys were investigated systematically. The results show that, whenSn content varies from0.2to0.6mol, the microstructures of the alloys still aredendrites. A new FCC(FCC3) solid solution with high Sn content forms in the alloysand the alloys are composed of FCC1, FCC2and FCC3solid solution. When Sncontents are0.8and1.0mol, only FCC1and FCC2solid solution exist in the alloys.The yielding strength and microhardness increase as the Sn content increases. When Sn content is1.0mol, they reach1102MPa and391HV. CoCrFeNiCu2Snxalloys exhibitexcellent compressive deformation properties and without fracture after23%deformation at1×10-4s-1strain rate.The effects of Nb element with high melting point on the microstructures,compressive properties and microhardness of CoCrFeNiCu2Nbxalloys wereinvestigated systematically. It was found that, the microstructure of CoCrFeNiCu2Nb0.2alloy still is dendrites，but a small amount of BCC solid solution with Nb elementprecipitates in interdendritic zones of the alloy, and it is composed of FCC1, FCC2andBCC solid solution. When Nb contents are0.4and0.6mol, the microstructures of thealloys change significantly. They are composed of the matrix structure of FCC2andsnowflake structure of BCC. The yielding strength, fracture strength and microhardnessof CoCrFeNiCu2Nbxalloys increase as the Nb content increases. When Nb content is0.6mol, they reach1118MPa,1202MPa and522HV respectively. Meanwhile thecompressive deformation properties of the alloys seriously decrease, and the samplesfractured after5.2deformation at1×10-4s-1strain rate.