Wear and coating removal mechanism of alumina/titania nanocomposite layer fabricated by plasma electrolysis

Adhesive wear of commercially pure titanium samples, coated with a nanocomposite layer of hard alpha alumina nanoparticles in titania based matrix, was analysed under standard wear tests. Different amounts of alpha alumina in a mixed silicate based electrolyte were used in order to improve the mechanical properties of the fabricated layers by plasma electrolytic oxidation on the surface of titanium based alloys. Concentration of alumina nanoparticles in electrolyte is an effective factor in the coating process. Its effect was studied on the distribution of nanoparticles in titania based matrix. The performed tests consisted of the precise figure analysis of scanning electron microscope (SEM) images, energy dispersive spectroscopy (EDS), microhardness and wear mass loss rate of the coated samples. X-ray diffraction and atomic force microscopy were also used for phase and surface analyses of the coatings, respectively. SEM microstructures of the worn surfaces were used in order to analyse the type and the distribution of the removed areas during the wear tests. Our findings revealed that aluminium (coming from alumina nanoparticles) in the removed areas was lesser than in the other worn sites. This result indicates that agglomerated hard nanoparticles can affect the coating removal mechanism. More concentrations of nanoparticles will lead to more agglomeration of them and hence to a lower wear mass loss rates of nanocomposite coatings.