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29of the lubricants, including their behavior at low temperatures and their resistance to oxidation. The tribological properties of the new biolubricants have also been studied, analyzing their ability to protect the interacting surface from wear, as well as the level of friction generated during sliding. Moreover, the compatibility of the new formulated oil with all the seals present in the real application has been taken into consideration. The selected lubricant is now being tested in agricultural machinery from AGRIA.

In recent years, several improvements have been made concerning the wear of materials in sliding contact, thanks to the employment of Cr +6 -free hard coatings, their optimization, and the development of new deposition techniques and technologies. When solid lubricants, such as PTFE materials, are involved as sliding surfaces against steel material, roughness and hardness effects on friction and wear have to be taken into consideration, because they play an important role from the tribological stand point.The aim of this work is correlation of tribological measurements with surface characteristics, in particular coating material, roughness and hardness of a landing gear rod sealing system. A cylinder-on-flat specimen configuration was chosen in order to faithfully reproduce working conditions, using a coated steel cylinder sliding against PTFE samples. The PTFE material was homogeneously worn independently of the countermaterial/coating, while when sliding against the softer material, the wear of the rod was observed. A comparison between results previously obtained on NBR is provided.

The mechanical and optical properties of TiO2 and Al2O3 films deposited by DC reactive magnetron sputtering were analysed as a function of the deposition conditions. Two different sputtering powers and three different voltages targets which influence the pressure and the deposition rate were studied. The voltage corresponds to two different percentages of the turn down set point of the hysteresis curve and fully poisoned condition. As their optical application is the main functionality of these coatings, the transparency and the refractive index were investigated. However, the mechanical properties are the key factors for determining the performance of these systems in use. For this, the wear resistance of these coatings was studied through the analysis of the evolution of the friction coefficient with time and the analysis of the wear track. The corrosion resistance has been also analysed through electrochemical studies. The results reveal that there is a clear influence of the studied deposition conditions on the mechanical and optical properties of these films. However, while general conclusions could be drawn for Al2O3 films, for TiO2 films the tendency is not so clear and further work needs to be performed.