Suchergebnisse

Functionally graded aluminium matrix composites reinforced with SiC particles are attractive materials for a broad range of engineering applications in the automotive, aircraft, sports, military and aerospace industries, whenever a superior combination of surface and bulk mechanical properties are required. In general, these materials are developed for the production of high wear resistant components. Also, often this kind of mechanical part operates in the presence of aggressive environments, such as marine atmospheres. In this work, aluminium composites with functionally graded properties, obtained by centrifugal cast, are characterised by reciprocating pin-on-plate sliding wear tests against nodular cast iron. Three different volume fractions of SiC reinforcing particles in each functionally graded material were considered. Sliding experiments were performed with and without the presence of a lubricant (3% NaCl aqueous solution). All tests were carried out at room temperature, under a normal load of 10N and constant frequency (1 Hz) and stroke (6 mm). In the case of the lubricated tests, electrochemical parameters (corrosion potential) were monitored during sliding. The worn surfaces as well as the wear debris were characterised by SEM/EDS. Friction values were in the order of 0.42 for unlubricated conditions, but varied between 0.22 and 0.37 when the aqueous solution was present. Relatively high wear rates (over 110-6 gm-1) were obtained in both unlubricated and lubricated sliding. The volume fraction of SiC particles exerted a net effect on the tribological response of the composites, although conditioned by the presence or absence of the aqueous solution. A deleterious effect of the chloride aqueous solution on the degradation of the matrix, leading to the pull-out of SiC particles induced by the dissolution of the matrix/particle interface was evidenced. Observation of the worn surface morphology indicated that the presence of the lubricant modifies the protective action promoted by the combined effect ...

Textile composites have been used for various applications because of their enhanced strength/weight ratio and versatile properties compared to other materials such asmetals. Many studies have investigated the tribological behaviour of textilecomposites, but none have focused onthe tribological characterization of 3D multilayeredwoven reinforced textile composites. Five types of 3-plywoven interlocked structures with varying interlacements were used as reinforcement for the nylon fibre/polyester resin composites for the present study. The influence of the textile structure interlacement on the tribological properties of the composite material (in terms ofwear volume)was investigated in thiswork. Further, special attention was given to understand the effect of sliding frequency on the tribological behaviour and driving wear mechanisms. The tests were conducted on a new class of reciprocating sliding wear tester, in dry (unlubricated) conditions, under a fixed applied load of 20N by varying the frequency of oscillating motion (0.5≤f≤8 Hz). In addition, testswere also conducted, at a constant frequency of 4Hz and as a function of several loads (5Nto 40 N). Fromthese tests, a 3-plywoven reinforced composite with the best tribological performance as a function of frequency and load was identified. It was observed that the type of woven structure had an influence on the tribological properties. Therefore, the selection of a textile composite should be based on the load and frequency at the service condition. The wear mechanisms involved in the tribological process were also analysed ; The authors would like to express their gratitude for financial support provided by FCT, Portugal, through an individual project (SFRH/BPD/20344/2004), and an Asia Link program between the University of Minho, Portugal, and IIT Delhi, India, sponsored by the European Union. Thanks also to Mr. Sérgio Carvalho, who assisted with experimental work in the Tribology Lab at University of ...

Applications of coloured thin films can be found on the production of high-quality consumer products, such as eyeglass frames, wristwatch casings and wristbands. These components should possess scratch and corrosion resistant surfaces through the desired lifetime. Recently, metal oxynitrides, MeNxOy (Me = early transition metal) were proposed for decorative applications. In these materials, variations on the amount of oxygen allow the film properties to be tailored, originating a wide range of colours. Additionally, these materials should also fulfil the wear and corrosion requirements above referred. In the present work the corrosion behaviour of single layered zirconium oxynitride, ZrNxOy films, immersed in artificial sweat solutions, is described. Films were produced by rf reactive magnetron sputtering at a constant substrate temperature of 300 ºC, from a pure Zr target. The main processing variable was the flow rate of reactive. The corrosion resistance was evaluated by potentiodynamic polarisation tests and Electrochemical Impedance Spectroscopy (EIS) at different immersion times, at room temperature. The corrosion resistance of the films is strongly affected by the O/N ratio. A slight tendency to improving the corrosion resistance of the films was found with the increasing in the atomic fraction of oxygen. Nevertheless, pitting was found in all samples. However, the amount of pits seems to be strongly dependent not only on the composition of the film, but also on the processing-induced defects distribution. ; European Union, FCT- Portugal and European community ...