Tailoring microstructure and phase segregation for low friction carbon-based nanocomposite coatings

Friction has a direct relation with the energy efficiency and environmental cleanliness in all moving mechanical systems. To develop low friction coatings is extremely beneficial for preserving not only our limited energy resources but also the earth’s environment. This study proposes a new design for low friction carbon-based nanocomposite coatings by tailoring the microstructure and phase segregation,and thereby it contributes to better controlling the mechanical and tribological properties. Experimental findings and theoretical calculations reveal that high-hardness (18.2 GPa), high-adhesion strength (28 N) as well as low-internal stress (-0.8 GPa) can be achieved by a nanocrystallite/amorphous microstructure architecture for the nc-WC/a-C(Al) carbon-based nanocomposite coating;in particular low friction (~0.05) can be acquired by creating a strong thermodynamic driving force to promote phase segregation of graphitic carbon from the a-C structure so as to form a low shear strength graphitic tribo-layer on the friction contact surfaces. This design concept is general and has been successfully employed to fabricate a wide class of low friction carbon-based nanocomposite coating

The influence of structure changes in the properties of TiCxOy decorative thin films

The main purpose of this work consists in the preparation of titanium oxycarbide, TiCxOy, thin films, in which the presence of oxygen changed the film properties between those of titanium carbide and those of titanium oxide. Varying the oxide/carbide ratio allowed to tune the structure of the films between titanium oxide and carbide and consequently electronic, mechanical and optical properties of the films. The depositions were carried out from a TiC target by direct current, dc, reactive magnetron sputtering, varying the oxygen flow rate. The obtained results showed that the film's properties can be divided into 3 different regimes -- i) carbide, ii) a transition zone and iii) an oxide one. X-ray diffraction results revealed the occurrence of a face-centered cubic phase (TiC-type) for low oxygen content, also obtained in the TiC1.6(O) film, with a clear tendency towards amorphization with the increase of the oxygen flow rate. For the highest oxygen contents, the results revealed the development of a mixture of poorly crystallized TiO2 phases. The colour results indicated a strong dependence on the O/Ti ratio. A progressive reduction of hardness and residual stresses with the increase of the O/Ti ratio was also observed. The residual stresses, as well as the film structure, seem to play an important role on the adhesion of the coatings. The static friction coefficient revealed also some correlation with the mechanical properties, but mainly with the surface roughness.http://www.sciencedirect.com/science/article/B6TW0-4MWPSDM-2/1/0c4ebbd1524da639df7c8a6dfc51206

Property change in multifunctional TiCxOy thin films: Effect of the O/Ti ratio

TiCxOy films with various O/Ti ratios have been deposited by DC magnetron sputtering, using C pieces incrusted in a Ti target erosion area. Composition analysis revealed the existence of three different growth regimes: (i) zone I, corresponding to films with metallic-like appearance, and atomic ratios O/Ti below one; (ii) zone II, with films revealing interference-like colours, and atomic ratios O/Ti higher than 2. Between these two regions, there was a transition zone T, where the atomic ratio O/Ti is between one and two. The films within this zone revealed a brown colour. X-ray diffraction (XRD) structural characterization results showed an evolution from a mixed Ti(C,O) phase at lower O/Ti ratio, to a quasi-amorphous structure within zone T, and poorly crystallized rutile and anatase TiO2 at the highest O/Ti ratios (zone II). These different structural arrangements resulting from different film's compositions had clear effects on electrical resistivity, whose values increased from about 7 × 102 to 2 × 1011 [mu][Omega] cm with increase of the O/Ti ratio. Fourier-transform infrared spectroscopy (FTIR) was used to further confirm the different nature of films structure and, thus, to better understand their properties variation. The observed behaviour was found to be in straight correlation with those of XRD.http://www.sciencedirect.com/science/article/B6TW0-4KWK0WW-3/1/f0de0f5875ba8dd82aec3345e10bf93