Effect of Mo, Ga and Fe on the corrosion resistance of nanocrystalline NiAl alloy in acidic media

The effect of Mo, Ga and Fe, and their combinations on the corrosion resistance of mechanically alloyed NiAl has been studied using potentiodynamic polarization curves and linear polarization resistance techniques at room temperature. The corrosive medium consisted of 0.5 M H2SO4 and 0.5 M HNO3. The NiAl+6Mo alloy exhibited the best corrosion resistance in 0.5 M H2SO4; however, this alloy showed the lowest corrosion resistance in 0.5 M HNO3. With the exception of 6Ga and 2Mo+2Ga additions, all the other additions in the NiAl alloy had a detrimental effect on the corrosion resistance in 0.5 M H2SO4 and presented no passivation except for the alloy containing 6Fe. With respect to 0.5 M HNO3 solution, all the additions decreased the corrosion rate of the NiAl-base alloy by two orders of magnitude while their passivity was reduced. When the film formed on the alloy was flaw-free, the underlying region did not suffer severe corrosion and was not pitted, while for films containing flaws or any other discontinuities, the alloy suffered from corrosion.