Microstructure And Mechanical Properties Of FeNi-based High Entropy Alloys And Their Composites

High entropy alloys（HEAs）are generally composed of four or more elements with the concentrations ranging from 5%to 35 at.%.The high entropy effect caused by the reaction between the principal components leads to the formation of simple solid solution phase rather than complex compound phase in the alloy.HEAs commonly exhibit high strength and hardness,excellent mechanical properties at high or cryogenic temperature,good wear resistance,corrosion resistance,unique magnetic and electrical properties,which make them have great prospect for engineering application.In the present work,FeNi-based high-entropy alloys were prepared by mechanical alloying（A）and spark plasma sintering（SPS）.Ti,Nb and Al were introduced to prepare the composites.The alloying behavior,microstructure,mechanical properties and abrasion performance of high-entropy alloys and their composites were investigated.The main conclusions are as follows:（1）The results show that the process of alloying was completed within 30h.Simple face-centered cubic（FCC）solid solution phases were observed in all four components of high-entropy alloys,and BCC phases were found in the powders containing Cr element.The sintered bulks all consist of FCC phases,in which Fe₂₈Ni₂₈Mn₂₈Cr₈Al₈ shows a typical biphasic structure.Overall,these alloys possess excellent compressive properties.The strength and hardness of Fe₂₈Ni₂₈Mn₂₈Cr₈Al₈ increase with the addition of Al element,while the plasticity decreases slightly.（2）The addition of Ti significantly changed the structure of Fe₂₈Ni₂₈Mn₂₈Cr₈Cu₈ and Fe₂₈Ni₂₈Co₂₈Cu₈Mn₈.In the region with high Ti content,the grains are refined.Compared with other HEAs,Fe_25.2Ni_25.2Co_25.2Cu_7.2Mn_7.2Ti₁₀ exhibited good comprehensive mechanical properties,the yield strength,fracture strain and hardness value were 1785 MPa,21.2%and494 HV,respectively.But the wear resistance is lower than that of Fe_25.2Ni_25.2Mn_25.2Cr_7.2Cu_7.2Ti₁₀.Laves phase appeared in the alloy powder with the addition of Nb element.After SPS,complex structured phases formed in the samples,which led to the decrease of the plasticity of the alloys.（3）The composites were prepared by adding Ti,Al and Nb into Fe₂₈Ni₂₈Mn₂₈Cr₈Cu₈and Fe₂₈Ni₂₈Co₂₈Cu₈Mn₈.After sintering at 1000℃,all the composites formed the structure with main FCC+carbides.When sintering temperature rises to 1150℃,the phase composition of the composites has no obvious change except Fe_25.2Ni_25.2Mn_25.2Cr_7.2Cu_7.2Ti₅Al₅.The multi-scale structure has been observed in Fe_25.2Ni_25.2Mn_25.2Cr_7.2Cu_7.2Ti₅Al₅,which makes the hardness of the composites increase greatly while retaining a certain degree of plasticity.