Effect of inhibitor addition on the corrosion behavior of a grain boundary relaxed electrodeposited nanocrystalline Ni–P alloy

Corrosion behavior of grain boundary relaxed electrodeposited nanocrystalline Ni–P was studied in HCl media with and without the addition of inhibitor Glycine. The Ni-0.5P alloy bears a grain size of 12 nm which was found to remain unchanged despite the grain boundary relaxation heat treatment at low temperatures of 423–523 K. By employing a linear hardening rule the activation energy (Q) of relaxation was determined to be 34 kJ/mol which corresponds to relaxation controlled by triple junction diffusion. The potentiodynamic polarization tests and electrochemical impedance spectroscopy were conducted in 1 M HCl electrolyte on the as-deposited and grain boundary relaxed samples. The alloy in relaxed condition exhibited lower corrosion current density (i_corr) values of 5.68 × 10^–5 A/cm² compared to that in the as-deposited condition with i_corr of 1.74 × 10^–4 A/cm². However, in the presence of 0.01 M of corrosion inhibitor Glycine, the relaxed sample showed higher i_corr values of 1.11 × 10^–3 A/cm² in comparison with the as-deposited material with i_corr of 1.25 × 10^–4 A/cm². This inversion of corrosion behavior was suggested to be the result of grain boundary relaxation affecting the formation of protein–metal complexes, which in turn is dependent on the oxide forming tendency of the metal. This was corroborated through XPS analysis.