Abstract
In this study we use linear sweep voltammetry (LSV),electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV),immersion test, a combined dynamic LSV(t)-OCP(t), OM, SEM, and glancing-angle XRD (GXRD) to investigate the corrosion properties of AlxCrFe1.5MnNi0.5Mo0.1 (x = 0.15, 0.3, 0.5) high-entropy alloys that is similar to 316 type stainless steel. LSV results show that (1) corrosion resistance of AlxCrFe1.5MnNi0.5Mo0.1 in 0.5 M sulfuric acid solutionincreases with x, which is contrary to that of AlxCrFe1.5MnNi0.5 (x = 0, 0.3,0.5) of Chang, and that of AlxFeCoNiCrMo0.5 (x = 0.5, 1, 1.5, 2) of Wu in 2006, suggesting that the corrosion properties of alloys is influenced by the environmental alloying composition. (2) The corrosion resistance of alloys in 0.5 M sulfuric acid and 0.25 NaCl mixing solution decreases with x, showing that the intrinsic alloy determines the corrosion propertyin this case of defective passive film. (3) There is irregular influence effect of x on corrosion property for alloys in 1 M NaCl solution. EIS results in 0.5 M sulfuric acid show the double-layer passive film is likely to form and the total electrical resistance increases as time increases, conforming results from SLV. CV tests in 0.5 M sulfuric acid +0.25 M NaCl solution show that positive hysteresis loop enlarges as Al content, manifesting the severe pitting corrosion, and conforming results from OM. There is an obvious deviation of about 100 times for results from conventional immersion test and from LSV, which has long been noticed but not explained in references in the past. By a combined dynamic LSV(t)-OCP(t) proposed by this study, we observe that an increase in corrosion rate due to the dissolution of the passive film after long-term immersion in corrosive solution, and the deviation between LSV and VII immersion results comes from this increase in corrosion rate. In this study we successfully reduce this deviation to a reasonable degree. Compared to the as-cast, each of all the other states, such as the as-solutionized & quenched, the as-furnace-cooled, the 500℃ x 2 h-aged,the 500℃ x 48 h-aged, the 900℃ x 2 h-aged, and the 900℃ x 48 h-aged,has no obvious beneficial or detrimental effects on the corrosionproperties of alloys in this study. From G-XRD data we observe the composition of the corrosive film on the surface of the sample is related to the Al content in the alloy. Similar results are obtained for both x =0.30 and 0.50, but different for 0.15.