Nanoindentation hardness and structure of ion beam sputtered TiN, W and TiN/W multilayer hard coatings

The present study reports on the mechanical and structural properties of monolithic TiN and W thin films, as well as TiN/W multilayered thin films with bilayer periods Λ ranging from 2.7 to 50 nm. Films were grown by direct ion beam sputtering (DIBS) on Si and MgO substrates at room temperature. The phase composition, microstructure, and residual stress have been analysed using X-ray diffraction (XRD). Hardness has been determined using nanoindentation with a Berkovich tip. A huge increase in hardness of more than 150% compared to bulk value is found in sputtered W thin films, related to large residual compressive stress (− 4.8 GPa) associated with growth-induced point or cluster defects, small grain sizes (∼ 5 nm) and the presence of a β-W phase. For TiN/W multilayers, an increase in hardness is observed with decreasing bilayer period Λ, reaching a maximum value of ∼ 24 GPa at Λ = 2.7 nm. Neither delamination nor film fracture was observed at high peak load nanoindentation tests, suggesting that these multilayered coatings combine good adhesion, hardness and toughness properties.