REACH-Compliant Nickel-Based Metal Matrix Composites for Tribological Applications: A Sustainable Alternative to Hard Chromium from the MOZART Project

The MOZART project brings together partners from both industry and academia to address the challenging task of replacing hard chromium (HC) plating with a REACH‑compliant alternative capable of delivering comparable performance.[1] Chromium trioxide, the basis of HC coatings, is classified as carcinogenic, mutagenic, and sensitizing to skin and respiratory pathways, and must therefore be phased out under REACH. Nickel plating, already widely used in industry, represents a less harmful option, and literature demonstrates that nickel‑based metal matrix composites (MMCs) reinforced with hard ceramic particles can achieve hardness values close to those of HC coatings (≈1200 HV). Nevertheless, conventional nickel baths still present toxicity concerns, particularly due to the use of boric acid as a buffering agent, which is considered toxic to reproduction.[2]

In this context, Politecnico di Milano, as a partner of the MOZART project, developed nickel‑based nanocomposite coatings reinforced with hard ceramic nanoparticles using electrodeposition from a succinic acid bath. Succinic acid, a di‑carboxylic acid with dissociation constants of 4.2 and 5.6, provides effective buffering around the operating pH of 4.6, eliminating the need for boric acid. The most promising results were obtained by co‑depositing boron carbide nanoparticles within the nickel matrix. Optimal conditions were identified as 10 g/L of dry nanoparticles dispersed in the electrolyte using sonication and a current density of 30 mA/cm², with a total charge exchanged of 36 C.[3] From a tribological perspective, the coating exhibited a coefficient of friction (CoF) of 0.12 under dry sliding conditions, which remained stable until progressive reduction of the surface roughness occurred as a result of continuous sliding. These findings highlight succinic acid‑based electrolytes as a viable, REACH‑compliant pathway toward sustainable, high‑performance tribological MMC.

[1] European Union, Mozart project [Online]. Accessed on 10th December 2025. Available at https://www.mozart-project.eu/# n.d.

[2] European Chemicals Agency, Understanding REACH [Online]. Accessed on 10th December 2025. Available at https://echa.europa.eu/regulations/reach/understanding-reach n.d.

[3] Zoia F, Bernasconi R, Afzali P, Lopez LM, Magagnin L. Electrodeposition of REACH compliant boron carbide reinforced nickel composites for wear protection. Surf Coat Technol 2026;520:132996. https://doi.org/10.1016/j.surfcoat.2025.132996.