Characterization of the mechanical properties and failure modes of hard coatings deposited by RF magnetron sputtering

Chromium oxide coatings with thicknesses of several micrometers were deposited by RF magnetron sputtering at various oxygen flow rates and sputter powers on carbon steel and high speed steel (HSS) substrates, respectively. The compositions and structures of the coatings were characterized by EDS, XRD, and XPS. The mechanical properties of the coatings, in terms of hardness and reduced elastic modulus, were determined by nanoindentation technique. UMT was used to carry out scratch test to study the coating failure mode. Correlations between the mechanical properties of the coating and substrates and the coating failure mode are discussed, which reveal that the coating with a low thickness and high hardness underwent plastic deformation during the scratch process, while the thicker coating with a lower hardness failed in chipping or spallation. The substrate plays a more important role than the coating itself in determining the coating failure mode.