Research On The Microstructure And Mechanical Properties Of FeNiMn-based High Entropy Alloys

In recent years,a new class of metallic materials,high entropy alloy?HEA?,has become a research focus.The new alloying strategy in HEAs leads to four certain effects:high entropy,sluggish diffusion,severe lattice distortion and cocktail effects.The four effects make the high entropy alloy have many excellent properties.In this work,based on the two kinds of FCC-structured FeNiMn-based high entropy alloys,one is the equiatomic FeNiMnCo high entropy alloy,for improving the strength,by adjusting the relative contents of Al and Ti and adjusting Ti content separately,two new types of high-entropy alloys(FeNiMnCoTi_xAl_1-x and FeNiMnCoTi_x)were prepared.The other is the non-equiatomic Fe₄₂Ni₁₂Mn₃₆Al₈ high entropy alloy,by adding 2 at.%of V and rare-earth element Y respectively,the microstructure and mechanical properties were studied.The experimental results show that for the FeNiMnCoTi_xAl_1-x high entropy alloy system,as the Ti content increases and the Al content decreases,the structure changes from BCC to BCC+FCC dual-phase structure,then to BCC+FCC+Laves structure,and finally to FCC+Laves dual-phase structure.For the FeNiMnCoTi_x high entropy alloy system,with the increase of Ti content,the structure changes from FCC to FCC+Laves dual-phase structure.The FeNiMnCoTi_0.5Al_0.5 alloy and FeNiMnCoTi_0.5 alloy exhibited the relatively good comprehensive mechanical properties in the two systems,respectively.The compressive yield strength,fracture strength,and fracture strain of the FeNiMnCoTi_0.5Al_0.5 high can reach 1052.8 MPa,2402.4 MPa,and 20.5%,respectively.The Vickers hardness of the FeNiMnCoTi_0.5Al_0.5 alloys is 518.7 HV.The compressive yield strength,fracture strength,and fracture strain of the FeNiMnCoTi_0.5 alloy can reach 803.2 MPa,2300.4 MPa,and 34.1%,respectively.The Vickers hardness of the FeNiMnCoTi_0.5 alloy is 402.4 HV.The comprehensive performance of the FeNiMnCoTi_0.5 alloy is better than that of some CoCrFeNi-based and CoCrCuFeNi-based alloys.The effects of heat treatment at 1000°C on the microstructure and mechanical properties of the FeNiMnCoTi_0.5 high entropy alloy were investigated.Besides,nanoindentation measurements were performed on the alloys,and the nanohardness,the elastic modulus,deformation behaviors and indentation creep of individual phases were tested.Among the three high entropy alloys with non-equiatomic alloying elements,Fe₄₄Ni₁₂Mn₃₆Al₈ and Fe₄₂Ni₁₂Mn₃₆Al₈V₂ have a single FCC solid-solution structure.The Fe₄₂Ni₁₂Mn₃₆Al₈Y₂ high entropy alloy contains FCC and Laves phases,and has a dendritic structure.The inter-dendrite region is the Laves phase.During the compression experiments,the three alloys show excellent ductility so that no fracture occurring.The addition of rare earth Y element has much more obvious strengthening effect.The yield strength and hardness of the Fe₄₂Ni₁₂Mn₃₆Al₈Y₂ high entropy alloy are higher than that of other two alloys,and are 453.7 MPa and 234.0 HV,respectively.