Influence of the microstructure of Zn–Ni coatings on hydrogen effusion characteristics

Abstract

This study reports about the influence of the microstructure of electroplated Zn–Ni alloy coatings, especially the extent and characteristic of existing microcracks within, on hydrogen effusion characteristics at room temperature (RT) and 200 °C. For comparison, the behavior of an electroplated Zn coating was also investigated. The microstructures of the Zn and Zn–Ni coatings were examined by means of scanning electron microscope (SEM) and optical microscope (OM). These results were correlated with the hydrogen effusion profiles, which were determined by using a carrier gas hot extraction (CGHE) technique. In addition, a silver decoration method was applied to visualize the hydrogen effusion paths within the coatings. First both Zn–Ni electroplating processes exhibit less hydrogen absorption compared to Zn. In addition the microstructure of the Zn–Ni coatings, especially the characteristic and magnitude of the microcracks, significantly influences the hydrogen effusion characteristics. By using the silver decoration method according to (Schober in MTA 14:2440-2442, 1983) it could be proofed that for Zn–Ni hydrogen primary effuses along the microcracks and the interfaces of pustules within the coating. But the microcracks seem to promote the hydrogen effusion much more than the interfaces of the pustules.