ON THE INFLUENCE OF LOW-ENERGY TANTALUM ION-IMPLANTATION ON INDENTATION FRACTURE AND HARDNESS OF ALPHA-ALUMINA SINGLE-CRYSTALS

The prismatic (1120BAR) Plane of sapphire was implanted with different fluences of tantalum ions of an energy of 60 keV. The continuous indentation test with different orientations of the Knoop indenter was applied to study the mechanical properties of the material. The crack/twin pattern observed in the vicinity of the indentation mark was found to be dependent on both Knoop indenter orientation and the implantation fluence. Ion implantation with increasing fluence lead to reduction of the crack size. A more ductile behaviour of the modified sapphire was observed. The analysis of the registered indentation load/depth curves on the basis of the recently developed energy principle of indentation allowed to discuss the differences in indentation behaviour of implanted and virgin crystals. An attempt to explain the different kinds of ''steps'' observed on the loading curves of the indentation test is undertaken. The observed effects which last to a considerably higher depth than the location of the implant are assigned to radiation induced amorphization and generation of compressive stresses.