Study On The Preparation And Mechanical Properties Of CrMnFeCoNi High-entropy Alloy

Compared with the traditional alloys,high entropy alloys have a series of excellent properties,such as high strength,high wear resistance,high machining hardening,high temperature oxidation resistance,corrosion resistance and high resistivity.High entropy alloy has become an important research direction in the field of metal materials.CrMnFeCoNi is a typical high entropy alloy with single-phase Face Centered Cubic(FCC)structure which has good development potential and broad application prospects.In this paper,Cr,Mn,Fe,Co,Ni and Cu powders were mixed in accordance with different composition ratio.The powder of CrMnFeCoNiCu_x HEAs was prepared by mechanical alloying(MA).The alloyed powders were then sintered into alloy blocks by spark plasma sintering(SPS).Phase structures and microstructures of alloys were investigated by using XRD,OM,SEM,TEM and EDS.The Vickers hardness,relative density,compressive strength and fracture morphology of the alloy block were also tested to characterized the comprehensive properties.The results show that both CrMnFeCoNi HEA and CrMnFeCoNiCu_x HEA can obtain powder with single-phase FCC structure after mechanical alloying.After 40h milling,CrMnFeCoNi has been alloyed into FCC structure.The alloying speed slowed down when adding Cu element.The alloy block under the condition of 1100℃and 50MPa sintering remained single-phase FCC structure.The sintered alloy obtained ultrafine grain microstructure and good mechanical properties.At room temperature,the compressive strength of CrMnFeCoNi high-entropy alloy was 2390MPa,and the fracture strain was 47%.With the addition of Cu,the hardness,strength and plasticity of the alloy decreased.The influence of process control agents(PCAs)on the preparation of high entropy alloy by MA was investigated.It was found that different PACs have different impacts on alloying speed and alloying effect.5wt.%ethanol as the PCA worked best and it brought the highest proportion of producing powder.The sintered alloy had the best properties in the room temperature.Sintering temperature and sintering pressure for SPS were studied.With the sintering temperature increasing,the relative density and compressive strength and plasticity of the alloy block increased,the hardness and yield strength decreased.With the sintering pressure increasing from 35MPa to 50MPa,the relative density of the alloy block increased,the compressive strength,yield strength and plasticity decreased and the hardness remained constant.In summary,the sintered alloy prepared under 1100℃,50MPa showed the best comprehensive mechanical properties.The effect of prolonged heat treatment on CrMnFeCoNi high entropy alloy was studied.After the 12h heat treatment at 700℃or 900℃,the change of the microstructure and mechanical properties at room temperature was not obvious.However,the grain size increased significantly and the compress yield strength at room temperature decreased sharply after 12h heat treatment at 1200℃.The heat treatment results fully explains good high temperature stability of the CrMnFeCoNi HEA fabricated by MA and SPS.