The Benefit of Superelastic NiTi Addition on Corrosion Performance of Electroless Ni–P Coating During an Accidental Scratch Event

Abstract

Electroless Ni–P–NiTi composite coatings were prepared on API X100 steel substrates by incorporating Ti particles into Ni–P matrix followed by annealing Ni–P–Ti coatings. The scratch behavior of the as-deposited and annealed coatings under a high load was studied. It was found that the highest scratch resistance is achieved on the annealed 11.8 wt% Ti coating among all the coatings due to the formation of superelastic NiTi particles after annealing. Transformation toughening induced by superelastic NiTi particles significantly improves the toughness and scratch resistance of the annealed 11.8 wt% Ti coating. The effect of scratching on corrosion behavior was also investigated. Potentiodynamic polarization (PP) and electrochemical impedance spectroscopy (EIS) results revealed that the corrosion resistance of pre-scratched annealed Ni–P–Ti coating is higher than both the as-deposited Ni–P and Ni–P–Ti coatings. The highest corrosion resistance is achieved on the pre-scratched annealed 11.8 wt% Ti coating. The addition of NiTi particles into Ni–P matrix prevents crack nucleation and propagation during scratching process, which decreases the available surface area for localized corrosion and improves the corrosion resistance of the annealed 11.8 wt% Ti coating. This research reveals that the corrosion resistance of Ni–P coating is improved by the presence of superelastic NiTi particles within the Ni–P matrix during an accidental scratch event.