Flux Assisted Casting Preparation and Surface Property Evaluation of Aluminium Matrix Composites Reinforced with Carbide Nanoparticles

Abstract

In the present effort, Aluminium Matrix Composites (AMCs) reinforced with submicron TiC and WC particles of 0.5 to 1 vol% content were produced through a casting based process assisted by both: (a) the use of K2TiF6 as a wetting agent in order to enhance particle incorporation into the molten matrix and (b) mechanical stirring to limit particle clustering. The produced composites are compared as far as their microstructure, wear and corrosion behaviour are concerned. Microstructurally-wise, an almost uniform particle distribution was achieved in both cases of particle reinforcement, characterized by clustered and isolated particles located mainly at the grain boundaries. Particle incorporation was kept at high levels suggesting the beneficial action of the K2TiF6 salt, whereas particle clustering was limited mainly due to mechanical stirring. Various intermetallic phases were formed as a result of both the inoculation by the K2TiF6 salt and the intensive reactivity of the ceramic phases with the molten matrix. The latter was mostly attributed to the ultra fine particle size. A eutectic microconstituent was also observed at the grain boundaries. Solidification front – particle interactions were found to also account for the final particle distribution and location. Sliding wear experiments revealed a beneficial action of the reinforcing phase on the wear response of the produced composites compared to that of the monolithic matrix. Surface oxidation, plastic deformation, crack formation and debris abrasive action were the main degradation features. Potentiodynamic polarization testing in Dilute Harrison's Solution (DHS) suggested similar corrosion mechanisms irrespectively of the type of the reinforcement phase. The performed analysis revealed localized corrosion effects mostly associated with the matrix alloy. Corrosion was largely associated with the eutectic microconstituent and the grain boundaries. Areas with a high concentration of sub-micron-particles had remained essentially free of corrosion signs.