Mechanical properties and tribological behaviour of nanolayered Al/Al 2O 3 and Ti/TiN composites

Abstract

Mechanical and tribological properties of nanolayered composites of Al/Al 2O 3 and Ti/TiN were investigated. Alternating layers of metals and ceramics were deposited using an r.f. magnetron sputtering technique. Nonoindentation tests were performed to determine force-displacement curves which were used to calculate elastic moduli and nanohardness of composites as a function of distance between layers. It was observed that both elastic modulus and hardness of composites increased with decreasing layer thickness. A good agreement was found between experimentally determined values for elastic modulus and predictions based on the rule of mixtures for isostress conditions. The hardness of Al/Al 2O 3 and Ti/TiN could be described in the formalism of the Hall-Petch-type equation indicating that ceramic layers inhibited slip transfer across metallic layers. A deviation from the Hall-Petch type of strengthening was observed in Al/Al 2O 3 at small interlayer spacings. Friction and wear behaviour of laminates was studied using a pin-on-disc type of tribometer. A systematic increase in wear resistance with decreasing layer thickness was observed. The peak friction coefficient decreased about 70% in Al/Al 2O 3 (with 200 nm Al layer thickness) while a significant 60% improvement in steady state friction coefficient was measured in Ti/TiN (with 150 nm Ti layer thickness) in comparison with as-sputtered monolithic metallic films. These observations indicated that the nanolaminated films are suitable for applications where a combination of low coefficient of friction, high wear resistance and hardness is required.