Efficient and environmentally friendly coatings on Ultra-High Strength Steels for the aerospace sector

The H2Free project will develop a degassing model which will look for the substitution of Cd by Zn-Ni, in a more environmentally friendly coating.

Ultra-High Strength Steels are used due to their extraordinary resistance mainly for landing gears in the aeronautic industry. To increase their corrosion resistance these materials require a coating which has usually included cadmium (Cd) as part of its chemical composition, a heavy metal with a high toxicity level whose use it is advisable to avoid. In line with the strategy for moving towards a more sustainable scenario in which the environmental impact is reduced, the European aviation sector is working on substituting Cd with innovative, environmentally friendly coatings. According to this new approach zinc/nickel (Zn-Ni) has been considered a feasible and non-toxic substitute, although its standardisation is not easy due to the degasification process to which it must be submitted in order to avoid the hydrogen embrittlement of the UHSS.

The aim of the H2Free project as part of the European CleanSky2 macro programme, is to develop a practical guide for the degasification of hydrogen from UHSS steel coated with LHE-Zn-Ni and LHE-Cd (Low Hydrogen Embrittlement zinc/nickel and Low Hydrogen Embrittlement cadmium) to save production costs and to minimise environmental impact, as well as enabling Zn-Ni to surpass the conventional toxic Cd coatings. It turns out that the lack of knowledge about the degassing kinetics means that we cannot know in advance if a standard degasification process is always necessary or effective in lowering the H content below the critical level, leading in some cases to scrap preventively entire components.

As explained by PhD. Garikoitz Artola, AZTERLAN,  “the hydrogen absorbed by the material generates an embrittlement level that leads to an increased risk of component fracture known as Hydrogen Induced Cracking (HIC), which favours the apparition and growth of cracks. Because of that, controlling the presence of this element is a critical factor to ensure a proper and safe performance of metallic components exposed to specific working conditions”.

Up to the date, AZTERLAN Metallurgy Research Centre has widely studied this phenomenon with the aim of generating a better understanding that will make possible to develop better performance materials and coatings. Within the H2Free project “AZTERLAN will study the hydrogen embrittlement of UHSS to determine the fittest manufacturing/degassing process conditions”.

The H2Free project will be developed by a consortium made up of four outstanding research centres and two SMEs with complementary profiles and great experience: The members from the Basque Research & Technology Alliance CIDETEC Surface Engineering (project leader) and AZTERLAN Metallurgy Research Centre, along with HELMHOLTZ-ZENTRUM GEESTHACHT, ELSYCA, ELHCO and the MAX-PLANCK-INSTITUT FÜR EISENFORSCHUNG.

H2Free is funded by the EU Horizon 2020 Framework Research and Innovation Programme and it is managed by Clean Sky Joint Undertaking (CSJU) through the CleanSky2 grant programme.

Graphic representation of Hydrogen Induced Embrittlement.