Conversion coating distribution on rough substrates analyzed by combining surface analytical techniques

摘要

In order to describe the chemical composition and the distribution of a thin trivalent chromium conversion coating on rough electrodeposited Zn-based alloy substrate, a methodology combining surface analytical and sputtering techniques was used. A sputtering by argon in glow discharge optical emission spectrometry (GD-OES) and by oxygen using time-of-flight secondary ion mass spectrometry (ToF-SIMS) were used to monitor the in-depth chemical composition evolution of the conversion coating and define the metal-conversion coating interface. Surface topography measurements were performed by high resolution 3D optical microscope. The chemical characterization of the conversion coating on the top surface and near the rough metal-oxide interface inside the craters was performed by X-ray photoelectron spectroscopy. The local depth and composition of the conversion layer inside and outside the craters were performed by Auger electron spectroscopy nanoprobe equipped with coaxial detector to prevent from shadowing effect during measurement. The results indicated inhomogeneous sputtering inside the ToF-SIMS craters, which was attributed to the shadowing effect, caused by the roughness of the substrate and the 45° incidence angle ion gun. GD-OES sputtering appeared homogeneous in different areas inside the crater despite the roughness of the substrate, which was attributed to the perpendicular incidence angle of the sputtering.