Study On The Preparation And Strengthening Of FeCoNiCrMn High-entropy Alloy By Powder Metallurgy

Compared with traditional alloy materials,high entropy alloys?HEAs?has attracted extensive attention in recent years due to its advantages of high strength and high hardness.The classical FeCoNiCrMn HEA is an important research direction in HEAs.In our study,FeCoNiCrMn HEA was prepared by powder metallurgy.CNTs/FeCoNiCrMn composites were prepared by adding CNTs.The preparation process was studied and the strengthening mechanism was discussed.The research contents are as follow:In this paper,a powder metallurgy method was used to prepare FeCoNiCrMn high-entropy alloy with equal atomic ratio.The alloying effect and the evolution of microstructure and mechanical properties of high entropy alloys under different ball milling conditions were studied.Considering both alloying effect and the efficiency of obtaining powder,the ball milling speed was chosen as 300 r/min and 400 r/min with the n-heptane as a process control agent,FeCoNiCrMn HEA powders with FCC single-phase solid solution structure can be effectively obtained by ball milling for 90h and 40 h respectively.After discharge plasma sintering?SPS??1000?and 15 min?can obtain high dense FeCoNiCrMn HEAs bulk materials.Two FeCoNiCrMn HEAs which obained from two ball milling speeds have similar microstructure and mechanical properties,but at 400 r/min can produce HEA powders more efficiently.Therefore,when n-heptane is used as the process control agent,400 r/min ball grinding for 40 h is a relatively appropriate ball milling process.The nanometer precipitated phases dispersed Cr and Mn elements,Cr₂₃C₆ compounds and FeCoNiCrMn HEA matrix together made up the structure of bulk HEA.Its compressive strength reaches 2030 MPa,yield strength is 1121 MPa,and its compressive plastic deformation can reach 38.2%.The fracture mode is quasi-cleavage fracture.In order to further improve the mechanical properties of FeCoNiCrMn HEA,this paper prepared CNTs/FeCoNiCrMn composites by powder metallurgy based on the alloy powders prepared,and studied the effect of CNTs addition on the microstructure and mechanical properties of the composites.With the increase of CNTs content,more aggregates were formed by CNTs,and the content of C compounds in HEA powders presented a trend of increasing first and then decreasing.At the same time,with the increase of CNTs content,the damage degree of CNTs surface in the composite powder increased first and then decreased gradually.Compression mechanical properties of HEAs will reduce with the increased of CNTs content gradually,when CNTs content is 0.2 wt.%,the compressive strength and yield strength at 2264 MPa and 1442 Mpa respectively,compression deformation is 41.6%,showing the best comprehensive mechanical properties,better than simple FeCoNiCrMn HEAs.The fracture mode of the composite changed from quasi-cleavage fracture to microporous aggregate fracture,and the number of dimples at the compression fracture increased obviously;the fracture mode of the composite material was completely transformed into a microporous aggregate fracture,but the plasticity of the material decreased due to the high porosity and low density when the content of CNTs reached 1.2 wt.%.