Effect of Nb-content on the corrosion resistance of Co-free high entropy alloys in chloride environment

This study investigated the effect of Nb-content on the corrosion behavior of the Al_(7)Cr_(20)Fe_(35-x)Ni_(35)Mo_(3)Nb_(x)(x=0,1 and 2)high-entropy alloys in a Cl-environment.The results indicated that only the face centered cubic phase existed in the NbO and Nbl alloys,while the emergence of Laves phase was observed when Nb-content reached 2 at.%.The NbO and Nb1alloys exhibited pitting corrosion,while the NiAl-rich phase experienced localized preferential corrosion in the Nb2 alloy.The electrochemical results revealed that the corrosion current density of the Nbx(x=0,1 and 2)alloys fell within the range of 10^(-8)-10-7 A·cm^(-2),with a pitting corrosion potential exceeding 700 mVSCE.Notably,the Nb1 alloy exhibited the most impressive corrosion resistance,as its corrosion current density(7×10^(-8)A·cm^(-2))was merely half that of 316LN stainless steel.This is attributed to its rapid passivation process,resulting in the development of a protective film characterized by an increased Cr_(2)O_(3)/Al_(2)O_(3)+Cr(OH)_(3)ratio.This study highlighted that the addition of Nb contributed to gram refinement,decreased corrosion current density,and elevated pitting potential,favoring passivation and improving corrosion resistance.However,excessive Nb-content resulted in the emergence of the Laves phase,inducing galvanic corrosion and diminishing resistance to corrosion.