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

Abstract

In this work, the electrochemical potentiodynamic polarization and impedance spectroscopy analysis were used to investigate the corrosion behaviors related to microstructural evolutions of Al0.3CoCrFeNiSix and Al0.3CoCrFeNiTix 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 Six alloys with increasing Si content. Furthermore, the reduction in the grain sizes of Six alloys with increasing Si content could also improve corrosion resistance of the alloys. Therefore, the corrosion resistance of Six 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 Tix 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 Ti0.3 alloy had the best corrosion resistance in Tix alloys. The analysis of X-ray photo-electron spectroscopy (XPS) identified that the contents of oxidized Cr3+ and Fe3+ in the passive film are the main contribution to improve the corrosion resistance of Six alloy. And the contents of oxidized Cr3+ and Ti4+ in the passive film are the main contribution to improve the corrosion resistance of Tix alloy.