Research On The Structures And Properties Of Ti-containing High Entropy Alloys

Due to a combination of high entropy,lattice distortion,sluggish diffusion and Cocktail effects,high entropy alloys（HEAs）possess unique structures and properties distinct from traditional alloys that have one major element.HEAs hold promises for a variety of applications,such as high strength alloys,corrosion resistant alloys,high temperature alloys and low temperature structural alloys.Therefore,they have attracted more and more attention in recent years.In present work,the effect of Ti addition on the microstructure,mechanical properties and corrosion properties of NbMoTaWTi_x,AlCrFeNiMo_0.5Ti_x and Al_0.5CrFeNiTi_x HEAs has been studied.NbMoTaWTi_x（x=0,0.25,0.5,0.75 and 1）HEAs have been developed based on a Nb-Mo-Ta-W alloy system.The room temperature strength and ductility of the NbMoTaWTi_x HEAs are improved by Ti alloying.Among the NbMoTaWTi_x HEAs,NbMoTaWTi alloy exhibits a yield strength of 1145 MPa and ductility of 11.5%at room temperature,while it possesses a yield strength of 586 MPa at 1200?C.In particular,NbMoTaWTi HEA keeps the microstructure stable at 1400?C.The ductility of single-phase refractory HEAs is found to be related to the mixing enthalpy（ΔH）and valence electron concentration（VEC）.Formation rule that requirs VEC<5.4 andΔH>-13.5 kJ/mol has been proposed for ductile single-phase refractory HEAs.This rule could be the criterion for the design of high performance single-phase refractory HEAs.AlCrFeNiMo_0.5Ti_x（x=0,0.25,0.4,0.5,0.6 and 0.75）HEAs have been produced.They possess excellent mechanical properties and corrosion resistance.With Ti addition,the strength and corrosion properties of AlCrFeNiMo_0.5Ti_x HEAs are improved,while the ductility decreases.Specifically,AlCrFeNiMo_0.5Ti_0.5.5 alloy possesses a yield strength of 2229 MPa and ductility of 10%at room temperature,while it possesses a yield strength of1120 MPa at 800?C.Furthermore,Al_0.5CrFeNiTi_x（x=0,0.1,0.2,0.3,0.4,0.5and 0.6）HEAs have been developed,which possess excellent mechanical properties and corrosion properties.Both the strength and corrosion resistance of Al_0.5CrFeNiTi_x HEAs have been enhanced with Ti additions.Among the Al_0.5CrFeNiTi_x HEAs,Al_0.5CrFeNiTi_0.4.4 alloy possesses a yield strength of 2324MPa and ductility of 21.9%at room temperature.