Tribofilm Formation As a Result of Complex Interaction at the Tool/Chip Interface during Cutting

Investigation of the Wear Performance of TiB2 Coated Cutting Tools during the Machining of Ti6Al4V Alloy

The machining of Ti6Al4V alloy, especially at low cutting speeds, is associated with strong Built-Up Edge (BUE) formation. The PVD coatings applied on cutting tools to machine such materials must have the necessary combination of properties to address such an underlying wear mechanism. The present work investigates and shows that TiB₂ PVD coating can be designed to have certain mechanical properties and tribological characteristics that improve machining in cases where BUE formation is observed. Three TiB₂ coatings were studied: one low hardness coating and two high hardness coatings with varied coating thicknesses. Wear performances for the various TiB₂ coated carbide tools were evaluated while rough turning Ti6Al4V. Tool wear characteristics were evaluated using tool life studies and the 3D wear volume measurements of the worn surface. Chip morphology analyses were done to assess the in-situ tribological performance of the coatings. The micro-mechanical properties of the coatings were also studied in detail to co-relate with the coatings’ performances. The results obtained show that during the rough turning of Ti6Al4V alloy with intensive BUE formation, the harder TiB₂ coatings performed worse, with coating delamination on the rake surface under operation, whereas the softer version of the coating exhibited significantly better tool life without significant coating failure.

Friction- and Wear-Reducing Properties of Multifunctional Small Molecules

Nitrogen- and oxygen-containing compounds were designed empirically and subsequently synthesized, and their rheology, friction, and wear performance as multifunctional base oils (MFBOs) were evaluated. Two of the compounds displayed good viscosity/rheology profiles without the addition of polymeric viscosity modifiers, displaying high viscosity indexes (VIs) above 200. Furthermore, all three MFBOs had lower coefficients of friction compared to well-established and accepted benchmarks. The most significant advancement is their impressive wear improvement by a factor of 5.5 to 70 compared to either of the benchmarks, which is attributed to the polar nature of the base oil which promotes boundary lubrication with metal surfaces. Moreover, these compounds were easily synthesized in one step from commercial starting materials. This work demonstrates that a careful design could provide the features/performance/functions of base oil, rheology modifiers (or VI improvers), and antiwear and friction-reducing additives, all-in one molecule.