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This page was translated automatically using artificial intelligence (DeepL). The German version is binding. More information about automatic translation
Electroplating, through the electrochemical deposition of metal, alloy and dispersion layers, is an important coating technology for resource-efficient manufacturing and for extending the service life of components and tools. By controlling the electrolyte composition and the deposition process parameters – such as pH, temperature and exposure time – the layer properties required for the subsequent application can be specifically tailored. A distinction is made between functional requirements (wear and corrosion protection) and decorative requirements (appearance, lustre). Hard chrome coatings in particular have a wide range of applications due to their outstanding properties. They are characterised by high coating hardnesses of 600 to 1200 HV1, as well as very good wear and corrosion resistance. Typical examples of components coated with hard chrome include cylinders, shafts and pistons in mechanical engineering, plant engineering and automotive manufacturing.
Since September 2017, the European Chemicals Agency (ECHA) has prohibited the use of hard chrome electroplating solutions without authorisation, as compounds containing chromium (VI) are considered to be carcinogenic2. Following the ban, many new coating processes and coating systems were developed with the aim of replacing hard chrome coatings. To date, no process or coating system has been able to fully replicate all the properties of hard chrome whilst taking manufacturing costs into account³.
The current ‘NiWRe-Alloys’ project is investigating nickel-tungsten (Ni-W) and nickel-rhenium alloy layers as substitutes for hard chrome layers. The research focuses on the development of a Ni-W alloy electrolyte. The combination of the material properties of nickel and tungsten, whilst taking cost into account, offers a potential alternative to hard chrome coatings.
The latest experimental results show that tungsten co-deposition without citrate can be achieved using a further-developed Watt’s nickel electrolyte. Furthermore, tungsten mass fractions in the range of 3 to 7 per cent were achieved through investigations using a rotating disc electrode (RDE).
Further hydrodynamic investigations were carried out on a beaker scale. The Ni-W layers deposited during these experiments were characterised using SEM-EDX (Figure 1), X-ray diffraction and microhardness testing. The topography of the deposited layers was measured using a laser scanning microscope (Figure 2).
Scott Dombrowe has been employed as a research assistant in Professor Dr. rer. nat. Frank Köster’s Surface and Electroplating Technology research group since 2019. He completed his Bachelor’s degree (2016) and Master’s degree (2019) at Mittweida University of Applied Sciences in Mechanical Engineering, specialising in Materials and Surface technology. Furthermore, he has been a certified international welding engineer since 2018 and is currently undertaking a joint PhD programme between Chemnitz University of Technology and Mittweida University of Applied Sciences. Alongside his professional work, he keeps bees as a hobby and is passionate about nature.
Addendum: Scott Dombowe presented this paper at NWK23 at Harz University of Applied Sciences, where, alongside numerous other academic talents, he encountered another type of ‘student’ that features on the Red List – a stag beetle.
Text and images: Scott Dombrowe
Endnotes
1 Schade, D. C. (9 March 2013). Electroplated chromium – A look at the mechanical properties. WOTech Technical Media | WOMag | WOClean. https://www.wotech-technical-media.de/womag/ausgabe/2013/03/09_w_Chromschicht_cs_03j2013/09_w_Chromschicht_cs_03j2013.php
2 REACH: Commission imposes strict conditions on the use of hazardous chemicals in the automotive, aerospace and medical sectors. (15 February 2019). Internal Market, Industry, Entrepreneurship and SMEs. https://single-market-economy.ec.europa.eu/news/reach-commission-imposes-strict-conditions-over-use-hazardous-chemicals-used-automotive-aerospace-2019-02-15_en
3 Wang, S., Ma, C. & Walsh, F. C. (2020). Alternative tribological coatings to electrodeposited hard chromium: a critical review. Transactions of the IMF, 98(4), 173–185. https://doi.org/10.1080/00202967.2020.1776962