In-situ formation of self-lubricating tribo-films for dry machinability

Significant reductions in friction coefficient during sliding tests of Cl-implanted TiN films were attributed to tribological reactions leading to the formation of TiO and shear deformable Magneli phase oxide (TinO2n−1), which are thought to act as a self-lubricant. Turning tests using cutting tools with Cl-implanted TiN and TiCN protective coatings have resulted in reduced friction and wear. pes of experiments have been carried out to study the formation of Ti-oxides in the presence of chlorine, and their relation to the improvement in dry machining performance. Firstly, unimplanted and Cl-implanted titanium films were oxidized in air at 400 °C to simulate in-situ oxidation in conditions similar to local heating during machining. Secondly, the oxide tribo-films formed on the cutting surface of unimplanted and implanted TiCN coated tools used in turning tests were examined in order to relate the oxide formation to improved cutting behaviour. icantly greater amounts of TiO and intermediate Ti-oxides including TiOx (1 < x < 2) and Magneli phases were found in the Cl-implanted samples analysed by X-ray photoelectron spectroscopy (XPS) in comparison to the unimplanted samples. The implanted chlorine atoms may have a catalytic role in the formation of Ti-oxides from Ti or TiCN. Furthermore, chlorine forms bonds with titanium, which reduces vacancies for oxygen during the oxidation reactions. This results in the formation of the lower order Ti-oxides instead of TiO2.