Comparative study on the corrosion behaviour of CNT-reinforced NiAl alloys in NaCl and Na₂SO₄ solutions

Various electrochemical techniques were used to study the corrosion behaviour of the CNT-reinforced NiAl alloys under NaCl and Na₂SO₄ environments. The potentiodynamic polarization curves revealed activation Tafel behaviour when the NiAl alloy specimens were immersed in NaCl solution while passivation followed by slight development of transpassivation resulted under Na₂SO₄ environment. The reinforcement of pure NiAl alloy with up to 1.0 wt.% CNT increased the corrosion rate from 0.10 to 0.63 mm/yr under NaCl environment, while under Na₂SO₄ environment, the corrosion rate increased from 0.04 to 0.12 mm/yr. The observed increase in corrosion rate with an increase in CNT reinforcement (under both NaCl and Na₂SO₄ environments) suggested that the reinforcement of NiAl alloys with CNT reduced the corrosion resistance of NiAl. The X-ray diffraction analysis revealed that the corrosion products consisted of oxides including Al₂O₃ under NaCl environment, while scanning electron microscope analysis showed a porous passive layer on the surface of the alloy specimens immersed in Na₂SO₄ solution. Graphical abstract: [Figure not available: see fulltext.]