Microstructure And Mechanical Properties Of FeNiCoCu System High Entropy Alloys And Their Composites

High entropy alloys(HEAs)typically consist of at least four elements with atomic concentrations of 5%-35 at.% for each element.Due to the high entropy effect and interaction among multi-principal components,solid-solutions with simple crystal structures are usually formed in these novel alloys.Normally,HEAs exhibit high strength,excellent thermal stability,exceptional wear and oxidation resistance,novel magnetic and electrical properties,which make them promising materials for engineering applications.In the present work,a series of FeNiCoCu high entropy alloys and their composites were fabricated by mechanical alloying(MA)and spark plasma sintering(SPS).The alloying behavior,microstructure and mechanical properties of these HEAs with different contents of Cu were studied systematically,as well as the effect of different preparation methods.The influence of Ti,Mn and Cr elements on the microstructure and properties were also studied.The microstructure and mechanical properties of FeNiCoCu based composites were investigated in detail,as well as the influence of different reinforcements and different sintering temperature.The main conclusions are as follows:(1)The processes of alloying were completed within 30 h and simple faced-centered cubic(FCC)structured phases were formed in the alloyed powders of all(FeNiCo)100-xCux high entropy alloys.Bulk FeNiCo alloy consists of single FCC structural solid solution without considering a trace amount of WC contaminants.(FeNiCo)100-xCux(x=10?15?20?25)alloys consist of FCC structured phase and a trace amount of iron oxides.Overall,these alloys possess excellent ductility,the strength increases with the increasing of Cu content.The grains of(FeNiCo)90Cu10 alloy were coarsened when the sintering temperature increasing,while it shows a lower strength and higher ductility.Compared with the 40 h wet-milling process,the SPS sintered FeNiCoCu alloy synthesized by 35 h dry-milling + 5h wet-milling powder exhibits similar strength and higher ductility.(2)The addition of Ti significantly changed the microstructure,in the mean time,two regions with different grain size were formed in the Ti-contained alloys.(FeNiCo)80Cu10Ti10 possesses excellent comprehensive performance and its compressive yield strength and strain at failure are 1639 MPa and 28%,respectively.The addition of Mn promoted the sintering properties,but it could not change the phase composition.The grain size of(FeNiCo)90Mn10 is less than 1?m,and the strength is obviously improved.The addition of Cr favors the formation of BCC phase in the MA process.The plasticity decreases for the formation of Cr-rich phase.The tensile yield strength,tensile strength and elongation of(FeNiCo)80Cu10Cr5Mn5 are 967 MPa,1011MPa and 6.6% respectively,which is superior to many existing HEAs.(3)Following 1000? sintering,the grains of FeNiCoCu based composites reinforced by TiC,WC and Al2O3 were refined while most of the reinforcements distributed in the fine region.B4 C could react with the HEA matrix to form complex structured phases.The addition of the reinforcements can increase strength in various degrees.After sintering at 1200?,the sintered properties of WC reinforced composite are deteriorated,and the microstructure of the composite with Al2O3 coarsens obviously.The TiC/FeNiCoCu composite displays the best high temperature stability.