Inorganic Fullerene-like (IF)-MoS₂ nanoparticles were tested under boundary lubrication and ultrahigh vacuum (UHV) and were found to give an ultra-low friction coefficient in both cases compared to hexagonal (h)-MoS₂ material. Previous works made by L.Rapoport et al. with IF-WS₂ ¹ reveal that the effect of the inorganic fullerene-like materials decreases at high loads and sliding velocities. Nevertheless, under the conditions used in our experiments, with high pressure (maximum pressure above 1.1 GPa in oil and 400 MPa in high vacuum) and slow sliding velocities (1.7 mm/s in oil test and 1mm/s in high vacuum), friction decreases and stabilizes at about 0.04 for 800 cycles in both cases. Therefore, IF-MoS₂ material appears to be a good candidate for use in various environments in regards to other structural MoS₂ forms. Wear mechanisms were investigated using both High Resolution TEM and surface analyses (XPS) on the wear tracks. Wear particles collected from the flat wear scar show several morphologies, suggesting at least two lubricating mechanisms. As the spherical particles are found in the wear debris, rolling may be a predominant event. However, flattened IF-MoS₂ particles are often observed after friction. In this case, low friction is thought to be due either to sliding between IF-MoS₂ external planes or to slip between individual unwrapped sheets ^2,3,4.

¹

(a). L. Rapoport et al., Nature, 387, 791 (1997).

(b). L. Rapoport, Y. Feldman, M. Homyonfer, H. Cohen, J. Sloan, J. L. Hutchison, and R. Tenne, Wear 975-982 (1999).

² C. Grossiord, J. M. Martin, T. Le-Mogne, and T. Palermo, Surface and coatings technology 352, 108-109 (1998).

³ C. Grossiord, J. M. Martin, T. Le-Mogne, K. Inoue, and J. Igarashi, Journal of vacuum science and technology, (1998).

⁴ C. Grossiord, K. Varlot, J. M. Martin, T. Le-Mogne, C. Esnouf, and K. Inoue, Tribology International, (1998).

Self-lubricant - Low friction MoS₂ / Ti (MoST) composite coatings (PVD magnetron sputtering) [1] has been deposited onto hard coating (PECVD) carbide inserts and have been tested for machining dry high speed milling and turning of steel and grey cast iron.

Dry machining (DM) is an important objective in machining industry to reduce environmental- and production costs. DM using MoST is possible in some cases: because of the low friction, the use of coolant is not necessary. Also better chip evacuation and a smoother cutting process will occur, which can lead to higher accuracy of products.

The paper includes an assessment of the limiting factors for a successful machining performance of coated tools including the influence of the geometry of the tool, the machining parameters.

These factors mentioned above have been correlated to the mechanical, chemical, oxidation and structural behaviour of the tools during machining tests.

[1] N.M Renevier, V.C Fox, D. G Teer, J. Hampshire, Surf. Coat. Technol., 127 (2000) 24

Plasma-sprayed Cr₂O₃-based coatings containing MoO₃ were studied to gain a better understanding of the influence of molibdenum oxide composition in the coatings on their tribological behaviour. Cr₂O₃/MoO₃ composite powders and a Cr₂O₃ powder were fabricated using a spray-drying method and plasma-sprayed coatings of these powders were produced.

Wear tests were conducted with a reciprocating motion at room temperature and 450°C under dry sliding condition. Measurement of friction coefficient was made in association with the sliding cycle. The physical characteristics of surfaces was investigated by scanning electron microscopy and chemical composition of the coating surfaces was analyzed using a X-ray photoelectron spectrometer and a transmission electron microscopy.

The study showed that the micro-hardness of coatings containing MoO₃ were higher than that composed of Cr₂O₃ alone. The result of TEM analysis indicated that chromium/molybdenum was precipitated in the grain and grain boundary. The friction coefficient of the MoO₃-added coatings were lower than that without MoO₃ addition at both test temperatures. However, the addition of MoO₃ in the Cr₂O₃ coatings did not significantly improve the anti-wear performance of the coatings at both test temperatures. Dispersed smooth films were formed in the worn surface for all coatings. These wear protecting layers, formed by plastic deformation of adhered and compacted debris particles to the surface, strongly influence the friction of the coatings as already observed by the authors with different plasma-sprayed coatings. The chemical composition of these films varied depending on the test temperature.

Today, special research activities are concentrated on the optimization of coating properties to improve the performance of cutting tools. (Ti,Al)N-based hard coatings are well known for their excellent microhardness even at elevated temperatures as well as for their good oxidation and wear resistance. Further improvements concerning the wear behaviour may be achieved by reducing the friction between tool and workpiece material in cutting.

In this paper, the cutting performance of hard and soft PVD-coated carbide tools is investigated in turning and drilling of tempered steel. Chip structure is analyzed in order to investigate the effect of friction. The cutting forces and the wear behaviour of the drilling process are highlighted for (Ti,Al)N and (Ti,Al)N+ a-C-coatings. A superior wear behaviour of soft coated tools was found in the initial wear phase. An influence of soft coatings on the wear behaviour after the running-in period could not be observed.