Electrodeposition and tribological characterisation of nickel nanocomposite coatings reinforced with nanotubular titanates

Metal nanocomposite nickel coatings reinforced with regularly shaped nanotubular titanates (multi-layered wall structure with c.a. 5 nm internal diameter and 30 to 500 nm tube length) were electrodeposited from a modified Watts nickel electrolyte. Tribological properties of the coatings are characterised by measuring the coating hardness, surface friction, wear rate and elastic modulus. Surface microstructures of the coatings were imaged (SEM and TEM analysis). The nanotubular titanates were shown to be embedded within the bulk of the coating and some particles protruded from the top surface. The nanotubular titanates in the nickel coating acted akin to a cross linked and mesh-like matrix to enhance the dispersion strengthening mechanism against external load. Nanocomposite nickel coatings reinforced with nanotubular titanates have shown (a) ~22 % reduction in surface friction against a spherical diamond tip, (b) ~29 % enhancement in wear resistance in a 3-body slurry abrasive wear test (steel counter body and 5 mm SiC particles), (c) ~50 % improvement in coating hardness and (d) ~21 % improvement in elastic modulus when compared with a nickel coating containing irregularly shaped nanosized titanium dioxide particles