The influence of low-energy ion bombardment on the microstructure development and mechanical properties of TiB x coatings

Abstract

The influence of the deposition parameters on the growth, structure and mechanical properties of the TiB x coatings is studied. The TiB x coatings represent a nanocomposite system, in which random or oriented TiB 2 nanocrystallites are embedded in an amorphous matrix as is revealed by cross-sectional transmission electron microscopy. We show that low-energy ion bombardment ( E i ) of growing TiB x coating, influences the preferred orientation of TiB 2 crystallites. The increase of ion current density ( i s ) by means of negative substrate bias voltage ( U s ) leads to change from random to the (0001) preferred crystal orientation whereby the electrical biasing promotes crystal growth in the coating and the (0001) texture appears gradually during the film growth. Together with the (0001) preferred orientation selection the composition B/Ti ratio was changed from 2.9 (floating potential, E i = 8 eV ) to 2.4 ( E i = 94 eV). The highest amount of oriented (0001) crystallites and highest hardness H = 53 GPa exhibit TiB x coatings deposited at E i = 94 eV and i s = 2.69 mA.cm −2.