Effect of macroalloying with Cu on the corrosion resistance of rapidly solidified NiAl intermetallic in 0.5 M H2SO4

The effect of Cu contents on the corrosion resistance of NiAl intermetallic rapidly solidified in 0.5 M H2SO4 at room temperature has been evaluated using electrochemical techniques. Cupper contents included 15, 20 and 25 wt.% and techniques included potentiodynamic polarization curves, linear polarization resistance and potentiostatic tests. For comparison, the same tests were performed on a 316L type stainless steels. The results showed that all the intermetallics exhibited a better corrosion resistance than the 316L type stainless steel for at least ten times but there was not a big difference between the different NiAl alloys with and without Cu for times longer than 4 h. For times shorter than 5 h, the corrosion current density of the NiAl alloys increased as the Cu contents decreased up to 20% but it increased when the Cu contents increased further up to 25%. A similar behavior occurred with the passive current density. These results were discussed in terms of the incorporation of cuprus oxide particles in to the external passive layer modifying its electrochemical properties. The pitting potential values decreased with additions of Cu respect to the unalloyed NiAl material. Corrosion morphologies showed a preferential dissolution of a phase respect to another due to the formation of micro galvanic cells due to the addition of Cu.