Hydrogen Permeation Study on Zinc-Nickel Coated Ultra-High Strength Martensitic Steels

Abstract

Cadmium coatings are conventionally electrodeposited on ultra-high strength steels (UHSS) used in aerospace application to provide corrosion protection. Zinc-nickel alloy coatings are being studied as an alternative to cadmium coatings as the latter exhibits environmental and health concerns. The electrodeposition of zinc-nickel alloy is accompanied by hydrogen evolution reaction, resulting in hydrogen incorporation into the coating and further inward diffusion into the steel substrate. Presence of hydrogen in UHSS leads to hydrogen embrittlement and can be detrimental to the properties. To avoid this, outgassing of the coated parts are carried out.In this work, the diffusion of hydrogen through zinc-nickel coated and uncoated UHSS was investigated using the Kelvin-probe based detection technique. The charging of hydrogen in the samples was carried out using either an electrochemical or hydrogen gas-based charging. A comparative study between the electrochemical and gas-based charging techniques was carried out. The influence of coating morphology on the permeation was studied to understand the influence of morphology on outgassing efficiency. The diffusion coefficients were derived from multi-step permeation measurements performed by varying activity at the entry side. This project has received funding from the Clean Sky 2 Joint Undertaking (JU) under grant agreement No 101007712. The JU receives support from the European Union’s Horizon 2020 research and innovation programme and the Clean Sky 2 JU members other than the Union.