Excellent strength-ductility synergy in a novel single-phase equiatomic CoFeNiTiV high entropy alloy

Abstract A new 3d transition metal high entropy alloy (3d TM HEA) CoFeNiTiV was prepared by vacuum arc-melting. The phase component, microstructure and mechanical properties of CoFeNiTiV alloy were investigated thoroughly, with the comparison of CoFeNiTi-base alloys. The results show that both CoFeNiTiV and CoFeNiTiAl consists of a typical single bcc phase, while the CoFeNiTiCr and CoFeNiTiCu alloys are both composed of a single fcc phase although they are all CoFeNiTi based alloys. The effectiveness of VEC has been confirmed in the studied alloy system. From the perspective of the elemental role on microstructure, Ti is beneficial to the formation of compounds, while the elemental V, Cu, Al or Cr promote the formation of single-phase solid solution. Moreover, the yield strength reaches 2730 MPa and ultimate compressive strength of CoFeNiTiV alloy is up to 3890 MPa, which is the highest of all CoFeNiTi based HEAs, even of all 3d TM HEAs up to date. Meanwhile, it exhibits a good ductility of 21.3%. This excellent strength-ductility synergy of CoFeNiTiV alloy might stem from the majority constitution of bcc phase, solid-solution strengthening, the strong bonding among the principal elements and the inhabitation of cracking nucleation owing to the uniform solute distribution.