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

The influence of the deposition parameters on the growth, structure and mechanical properties of the TiBx coatings is studied. The TiBx coatings represent a nanocomposite system, in which random or oriented TiB2 nanocrystallites are embedded in an amorphous matrix as is revealed by cross-sectional transmission electron microscopy. We show that low-energy ion bombardment (Ei ) of growing TiBx coating, influences the preferred orientation of TiB2 crystallites. The increase of ion current density (is) by means of negative substrate bias voltage (Us) 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, Ei = 8 eV) to 2.4 (Ei = 94 eV). The highest amount of oriented (0001) crystallites and highest hardness H = 53 GPa exhibit TiBx coatings deposited at Ei = 94 eV and is = 2.69 mA.cm−2.

Research highlights
► The influence of low-energy ion bombardment on TiBx coatings during deposition.
► The TiBx coatings represent a non-textured or preffer oriented nanocomposite system.
► TiB2 nanocrystallites are encapsulated within amorphous matrix.
► TiBx coatings exhibit high values of hardness (35–53 GPa).