TRIBOLOGICAL PROPERTIES OF NIOBIUM ION-IMPLANTED ALUMINA

This paper examines the effects of niobium ion implantation on the surface mechanical properties of single crystal and polycrystalline alpha-alumina. A structural transformation can be produced in sapphire implanted with a high fluence of niobium ions which leads to the formation of an amorphous layer of alumina containing nanoclusters of metallic niobium. Nanoindentation experiments are carried out to characterize the mechanical properties of the implanted layers. A low fluence implantation increases the Young's modulus but not the hardness. For high fluence, the amorphous transformation softens the material. The tribological behaviour is studied by comparing the friction kinetics in rotating and reciprocating motion. At low fluence, no difference between implanted and unimplanted samples is observed. For high fluence, the implantation increases the friction coefficient and the wear rate. The friction and wear of implanted alpha-alumina are governed by the behaviour of a transfer film.