Aluminium reinforced by WC and TiC nanoparticles (ex-situ) and aluminide particles (in-situ): Microstructure, wear and corrosion behaviour

Abstract

In the present effort, Aluminium Matrix Composites (AMCs) were produced by the addition of submicron sized TiC and WC particles of low (up to 1.0vol%) content into a melt of Al1050. Casting was assisted by the use of K2TiF6 as a wetting agent and mechanical stirring to limit particle clustering. An extensive presence of intermetallic phases was observed in the cast products, as a result of both the inoculation by K2TiF6 and the intensive – mainly due to the fine carbide particle size – reactivity of the carbides with the molten matrix. Particle distribution was reasonably uniform comprising both clusters and isolated particles. The intermetallic particle dispersion has changed the intended nature of the composites. Instead of one type of reinforcement, that of carbide particles, the aluminium matrix contained two main types of reinforcement: (a) in-situ intermetallic particles and (b) carbide nanoparticles, as such, or more often as clusters of remaining carbide nanocores and aluminide particles. The reinforced materials exhibited a notably improved sliding wear performance over that of the alloy owing to the beneficial effect of both the carbide and the intermetallic phase dispersion. A wear mechanism was formulated based on microstructural features of the wear surface (repeated “hill-valley” morphology, surface oxide layers, crack formation and grooving). Cyclic potentiodynamic polarization in Dilute Harrison’s Solution (DHS) revealed that the corrosion behaviour of the reinforced materials was mainly controlled by the corrosion of the alloy matrix. As such, the predominating form of corrosion was intergranular corrosion (IC) of Al associated with the presence of alloy matrix impurities. Carbide nanoparticles, aluminide phase associated with them and their Al-matrix remained essentially intact of corrosion. IC progress was often inhibited by the presence of clusters of aluminide and carbide particles.