The effects of P and metal elements in electroless nickel-based alloys on the formation of Ti/Zr conversion coating

Abstract

The objective of this study was to investigate the effects of P and different metal elements on the formation of Ti/Zr conversion coatings on various electroless nickel-based coatings. Advanced surface analytical techniques, including X-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, glow discharge optical emission spectrometry, and scanning Kelvin probe force microscope were utilized for comprehensive characterization. The results indicate that P in the electroless Ni-P plated coating had a minor impact on accelerating the formation process of the conversion coating by promoting nickel phosphate generation. However, the presence of Fe in the plating coating promotes the generation of nickel phosphate mainly by changing the potential distribution on the surface, which greatly facilitates the reaction for conversion coating formation. In addition, due to its higher activity compared to nickel, Fe participated in the redox reaction, resulting in a significant change in the composition and thickness of coating. Conversely, Cu did not participate in the redox reaction, but instead promoted the generation and thickening of the conversion coating by slightly changing the surface potential. These insights into the role of P, Fe, and Cu elements provide valuable knowledge for optimizing conversion coatings for specific applications, promising significant practical implications.