Sputtered DLC-TiB2 multilayer films for tribological applications

This study focuses upon the deposition of diamond-like carbon thin films for tribological applications. Carbon consists of mainly sp² bonds, having a low Hardness and low coefficient of friction. By depositing carbon in a methane (CH₄)-rich atmosphere, the energetics of the process favours the formation of diamond-like bonds, namely sp³. To improve the tribological properties of a multilayer system, a refractory metal ceramic TiB₂, has been multilayered with carbon and deposited on titanium (Ti) substrates to a total thickness of 3 μm. A multilayer stack of 10 bi-layers has been deposited, and the volume fraction of carbon in the coating has been varied by changing the thickness of the individual layers. This study employs pulsed-dc sputtering combined with Ar 7.5% CH₄ to deposit both carbon and TiB₂.The Raman spectroscopy data shows that the carbon deposited was amorphous in nature with an I_D / I_G ratio of 1.25. TiB₂ sputtered in Ar 7.5% CH₄ formed Ti-B-C, containing both a hard TiB₂ phase and a lubricating diamond-like carbon phase.Three volume fractions of carbon have been investigated: 25%, 50% and 75%. From nanoindentation studies, the Hardness varies from 5 to 3 GPa for the 75% and 25% carbon-containing coatings, respectively, measured at a penetration depth of approximately one-third of the coating. This increase in Hardness as a function of percentage of carbon has been attributed to the coatings forming load-bearing properties.From wear studies, friction coefficients of around 0.3 have been measured. Thus, these multi-layered TiB₂/C coatings are both load bearing and lubricious.