ABSTRACT Ta1-xZrxN thin films were deposited by reactive magnetron sputtering aiming to investigate the influence of zirconium addition on the microstructure, hardness and high temperature oxidation resistance of the coatings. GAXRD showed that all Ta1-xZrxN thin films maintained ZrN crystalline structure, forming a TaZrN solid solution. Zr incorporation did not alter hardness values of Ta1-xZrxN coatings, however, promoted significant improvements in the oxidation resistance when compared to pure TaN thin films.

NbxAlyNz thin films were deposited by magnetron sputtering reactive technique with (y/x+y) ratio varying from 0 to 0.4, in order to maintain aluminum atoms inside NbN matrix in solid solution. GAXRD analyses revealed that the crystalline phase obtained for NbxAlyNz thin films was B1-NbN with a lattice constant shrinkage as Al concentration at these coatings was increased. Due to similarity in electro negativity values between Nb and Al, XPS analyses could not verify pronounced changes among as deposited NbxAlyNz coatings. The average hardness values evidenced that solid solution strengthening mechanism did not increase hardness significantly. The oxidation resistance increased with Al content and no oxide phases were registered by GAXRD analyses for coating with more aluminum added. However, SEM images revealed bubbles after oxidation at high temperatures for all samples.

Zirconium silicon nitride (ZrSiN) thin films were deposited by reactive magnetron sputtering in order to verify the silicon influence on coating morphology and mechanical properties. The Si/(Zr+Si) ratio was adjusted between 0 to 15% just modifying the power applied on the silicon target. Only peaks associated to ZrN crystalline structure were observed in XRD analysis, since Si3N4 phase was amorphous. All samples have (111) preferred orientation, but there is a peak intensity reduction and a broadening increase for the sample with the highest Si/(Zr+Si) ratio (15%), demonstrating a considerable loss of crystallinity or grain size reduction (about 8 nm calculated by Scherrer). It was also observed that the I(200)/I(111) ratio increases with silicon addition. Chemical composition and thickness of the coatings were determined by RBS analysis. No significant changes in nanohardness with increasing Si content were found. The morphology observed by FEG-SEM presents non columnar characteristics for thin films with silicon addition. The set of results suggests that Si addition is restricting the columnar growth of ZrN thin films. This conclusion is justified by the fact that Si contributes to increase the ZrN grains nucleation during the sputtering process.

Biodiesel consists of long-chain fatty acid esters and it presents relatively inert behavior right after its production. However, structural changes occur during its storage, as this fuel has low oxidative stability, fact that increases its corrosivity. The problem of corrosion has become increasingly relevant due to the Government's policy of setting a gradual increase in the percentage of biodiesel added to diesel. The current study evaluated the effectiveness of three natural products to work as corrosion inhibitor in biodiesel. The evaluation was done by means of immersion tests and electrochemical impedance spectroscopy. Results showed that it is possible to reduce biodiesel influence on carbon steel corrosion and that it can be extend to other metals used in automotive engines.

The focus of this paper is to establish a characterisation method for seven polyamide (PA) grades to determine the major material to manufacture an automotive worm gear. The composite properties were measured according to the worm gear loadings: tensile strength, Young's modulus, abrasion and impact resistance. They were also correlated to the PA moisture absorption and its glass fibre (GF) reinforcement. The data from mechanical tests were applied in the finite element analysis (FEA) using the von Mises stress criterion. Before the rig tests of the PA worm gears, the injection process was evaluated, through the capillary rheometry. A higher difficulty to process PA 6/6 30% GF was found, due to its lower apparent viscosity. In the end, the influence of moisture absorption was as decisive to the gear's material selection as the GF to the pinion. Thus, the PAs with the best performance were: PA 6 with 30% GF (gear) and with PA 60% GF (pinion).