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In the current study, electro-deposition of hybrid coatings consisting of Cr simultaneously reinforced with nano-scale 3 mol% yttria-stabilized zirconia (YSZ) along with hexagonal boron nitride (Cr-YSZ-BN), graphene (Cr-YSZ-Gr), and diamond (Cr-YSZ-D) was performed using an environmentally-benign trivalent Cr bath. Abrasive wear with ploughing for scratch test is recognized as the dominant wear mechanism in coatings; on increasing the scratch speed, gross spallation occurs in the BN reinforced coatings. While graphene and diamond were strongly adherent to the substrate with no signs of delamination. During fretting, oxidative and three-body abrasive wear in wedge formation mode with severe crack networking was observed in Cr-YSZ-BN. Micro-ploughing was active with intermittent cracking in Cr-YSZ-Gr coatings, indicating lower wear (via solid-lubrication by graphene). Diamond added coating, on the other hand, exhibits fewer cracks with ploughing. High hardness and elastic modulus with a maximum of ~26 GPa and 245 GPa, respectively, were obtained for Cr-YSZ-D coating with a minimum wear rate of ~3.5×10−11 m3/Nm (fretting) and 3.8×10−5 mm3/Nm (scratching). Further, rigid sp3 hybridization of carbon atoms in Cr-YSZ-D leads to the strong interlocking between Cr matrix and diamond, thereby lowering the wear damage of the coating system. The unique combination and uniform dispersion of YSZ and diamond particles displayed enhanced friction and wear resistance (k ~ 1.4×10−3), primarily due to the inherent high hardness of diamond and matrix strengthening by nano and micro-scale particles. Therefore, Cr-YSZ-D coating system emerges out as a highly robust coating capable of providing enhanced damage tolerance towards wear for various tribological applications. • Synergistic YSZ reinforcement with BN, graphene, and diamond in Cr-matrix. • Reduced crystallite size (~15 nm) and high dislocation density (~1011 cm-2) in reinforced coatings. • High compressive residual stresses (~720–1230 MPa) in hybrid coatings. • High fretting damage tolerance (wear rate of ~3.5 × 10–11 m3/Nm) in Cr-YSZ-D hybrid coating. • Low micro-scratch damage (wear rate of 3.8 × 10-5 mm3/Nm) in Cr-YSZ-D hybrid coating. [ABSTRACT FROM AUTHOR]

In the present work, electrodeposited chromium coatings were strengthened with 3 mol% yttria-stabilised zirconia nanoparticles (YSZ) and carbon nanotubes (CNT) to analyse anti-corrosive and wear properties of the coatings. Highest hardness (~24 GPa), minimum scratch wear rate i.e. ~3 × 10−11 m3/Nm and highest corrosion resistance of ~3.9 kΩcm2 was obtained by synergistic incorporation of YSZ and CNT in Cr matrix. This can be linked to high dislocation density ~22 × 1011 cm−2 (Orowan effect) and compressive residual stresses i.e. ~840 MPa (Cr-YSZ-CNT), which tend to seal-up micro-holes and cavities, thereby, restricting the onset of wear and corrosion in the matrix. Addition of inert YSZ nanoparticles imparts chemical stability as well as hardness to the Cr matrix (~11 GPa for Cr-YSZ, ~8.4 GPa for Cr). Further, CNT incorporation, apart from matrix strengthening, results in low COF (~0.12) due to self-lubricating nature of CNTs, which leads to reduced wear rate of ~3.8 × 10−11 m3/Nm (Cr-CNT) with respect to Cr and Cr-YSZ. Thus, barrier protection and corrosion inhibition might be protective mechanisms for Cr-YSZ-CNT coating that make it suitable for engineering and industrial applications in order to protect the vital components exposed to tribological and corrosive media conditions. • Scratch and electrochemical behavior of Cr based electrochemical composite coatings • Cr-coating reinforced with yttria stabilized zirconia (YSZ), & carbon nanotube (CNT). • High compressive residual stresses in the range ~264-840 MPa in composite coatings. • Restricted wear rate (~3×10-11 m3/Nm) from micro-scratch in Cr-YSZ-CNT. • High corrosion resistance of ~3.9 kΩcm2 in Cr-YSZ-CNT coatings. [ABSTRACT FROM AUTHOR]