Effects of nano-WC content on morphology, hardness and tribocorrosion properties of Ni/nano-WC nanostructured hybrid coatings

Lidia BENEA, Pierre PONTHIAUX, Nadège CARON, Olivier RAQUET

1 Competences Centre: Interfaces-Tribocorrosion-Electrochemical Systems (CC-ITES), Faculty of Engineering, Dunarea de Jos University of Galati, 47 Domneasca Street, RO-800008 Galati, Romania.
2 Ecole Centrale Paris, Laboratoire Génie des Procédés Matériaux (LGPM), F-92290 Châtenay-Malabry, France.
3 Lasers and Surfaces Engineering Laboratory, CEA Saclay, F91191, France.
4 CEA, Nuclear Energy Division, Physico-chemistry Department, CEA Saclay, F91191, France.

In order to increase the hardness, reduce the friction coefficients and further improve the wear - corrosion (tribocorrosion) properties of pure Ni coatings, Ni/nano-WC nanostructured hybrid coatings were prepared on the surface of stainless steel by electrochemical co-deposition process of nickel with dispersed WC nanoparticles (mean diammeter of 60 nm). The effects of WC nano-particles content on the morphology, composition, hardness and tribolocorrosion properties of the Ni/nano-WC nanostructured hybrid coatings were investigated and compared to pure Ni coatings. The surface morphology and the composition of coatings were characterized by scanning electron microscopy (SEM) with energy dispersive analyzer system (EDX). Tacking into consideration the SEM morphologies, it was found that the presence of WC nano-particles change the crystallizations of nickel matrix to smaller and thinner crystallites.
The EDX analyzes proved the inclusion of WC nano-particles into nickel matrix. By comparatively nanoidentation technique it was found that Ni/nano-WC composite coatings exhibit improved nanohardness as compared with pure nickel coatings. The wear - corrosion behaviour of the pure Ni and Ni/WC nanostructured hybrid coatings were evaluated using a ball-on-flat fretting set-up, by applying different loads. The results show that the addition of WC nano-particles into to the Ni matrix may greatly reduce the friction coefficients and improve the wear resistance compared with pure Ni coatings.

Acknowledgment
UEFISCDI - Ministry of Education and Research is acknowledged for the financial support to Competences Centre Interfaces - Tribocorrosion and Electrochemical Systems (CC-ITES) - Dunarea de Jos University of Galati - Research Project: HyBioElect, contract 10 /30-08-2013 (2013 - 2016) in the frame of National Research Programme Romania - PN II PCE.