Corrosion behaviors related to the microstructural evolutions of as-cast Al0.3CoCrFeNi high entropy alloy with addition of Si and Ti elements

In this work, the electrochemical potentiodynamic polarization and impedance spectroscopy analysis were used to investigate the corrosion behaviors related to microstructural evolutions of Al 0.3 CoCrFeNiSi x and Al 0.3 CoCrFeNiTi x HEAs in the NaCl solution. The results presented that addition of Si promoted the formation of BCC phase, which was regarded as a micro-anode to prevent FCC phase as a micro-cathode from being corroded. While the volume fraction of BCC phase increased to enhance the corrosion resistance of Si x alloys with increasing Si content. Furthermore, the reduction in the grain sizes of Si x alloys with increasing Si content could also improve corrosion resistance of the alloys. Therefore, the corrosion resistance of Si x alloys was increased with increasing Si content. Addition of Ti with a high corrosion resistance of Clˉ caused the reduction in the grain sizes of Ti x alloys, which can improve the corrosion resistance of alloys. However, the high Ti content can destroy the corrosion resistance of the alloys due to the formation of a large amount of precipitated phases. Therefore, as Ti with atomic percentage be equal to that of Al can effectively eliminate the negative influence of precipitated phases and microstructure on the corrosion resistance of alloys, meaning the Ti 0.3 alloy had the best corrosion resistance in Ti x alloys. The analysis of X-ray photo-electron spectroscopy (XPS) identified that the contents of oxidized Cr 3+ and Fe 3+ in the passive film are the main contribution to improve the corrosion resistance of Si x alloy. And the contents of oxidized Cr 3+ and Ti 4+ in the passive film are the main contribution to improve the corrosion resistance of Ti x alloy. • Addition of Si promoted the formation of BCC phase; Addition of Ti promoted the formation of L1 2 , Laves, γ and σ precipitated phases. • Addition of Si causes the increase in corrosion resistance of Si x alloy due to BCC phase regarded as a micro-anode to prevent FCC phase as a micro-cathode from being corroded. • Ti element has a high corrosion resistance of Clˉ, Ti 0.3 has the best corrosion resistance in the Ti x alloys. • Addition of Si and Ti causes thegrain refinement to improve corrosion resistance of alloys. • The contents of oxidized Cr 3+ , Fe 3+ and Cr 3+ , Ti 4+ in the passive film are the main contribution to improve corrosion resistance of Si x and Ti x alloys, respectively.