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

Significant reductions in fiction 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. Two types 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 degrees 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 fori-nation to improved cutting behaviour. Significantly 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. (c) 2005 Elsevier B.V. All rights reserved.