Mechanical Properties of Nanocomposite Multilayers

This work s concerned with the mechanical properties of nanocomposite metal/ceramic multilayers. Three thin film nanocomposite systems, namely Al/Al₂0₃, Ti/TiN and Cr/C, have been investigated. The nanocomposites were synthesized on Si (100) wafers by using an electron-beam physical vapor deposition method. The microstructure of the films was characterized by transmission electron microscopy. The deposited metal layers Al, Ti and Cr possessed fcc, hcp and bcc structures, respectively, where the ceramic TiN layers had fcc structure and the Al₂O₃ and C layers were amorphous. The mechanical properties of the nanocomposite thin films were studied by conducting nanoindentation and microhardness experiments. The nanosize of the components was found to affect significantly the mechanical properties that were dominated by the thickness of the metal layer. The hardness response in all three systems can be described as a function of the metal layer thickness by a Hall-Petch relationship. A hardness increase was observed up to a 40 ma, 5 nm, and 20 nm layer thickness for the Al, Ti, and Cr layers, respectively. The effects by the ceramic phase were found to be significant only in films with metal layer thickness at or just before the critical thickness.