STRUCTURE AND MECHANICAL-PROPERTIES OF NANOLAMINATED TI-AL THIN-FILMS

The stability of crystal structures in multilayers of titanium and aluminum is influenced markedly by the bilayer thickness. Thus, as the bilayer thickness is decreased, the crystal structure of the titanium layers changes from hexagonal close-packed (hcp) to face-centered cubic (fcc) and then reverts back to hcp. In the case of the aluminum layers, there is a transition from fcc to hcp structure at very small values of the bilayer thickness. The reasons for these variations are not well understood, but they may well be influenced by the variation of stacking fault potentials. Nano-indentation has been used to derive the elementary mechanical properties of these multilayers, namely the Young's modulus and hardness. No super-modulus effect is observed as the bilayer thickness is reduced. The hardness values increase markedly as the bilayer thickness is reduced, following a Hall-Petch relationship with this parameter.