Fabrication of near net-shaped Al-based intermetallics matrix composites

Intermetallic compounds based on aluminium with Ni, Fe or Ti offer new opportunities for developing superior/advanced structural alloys for applications as diversified as biomedical and aerospace-aircraft industries. Aluminides have the attractive characteristics of low density, high strength, good corrosion and oxidation resistance, non-strategic elements and relatively low cost. There are several techniques for synthesizing the intermetallics and intermetallic matrix composites (IMCs), including the conventional melting and solidification, reactive sintering of constituent powders, and more recently the reactive infiltration of the low melting point constituent metal into the powder preform of the other constituents. The current project studied the fabrication of near net-shaped IMC via molten metal infiltration and subsequent reaction with the metal powder-reinforcement preform. X-ray diffraction (XRD), optical and SEM microscopes were used to characterize the infiltration, reaction and the resulted microstructure. It is expected that the molten metal temperature, holding time within the molten metal, the infiltration pressure, i.e. metallostatic pressure and the preform compaction pressure are all important parameters to be considered carefully to achieve sound components. The current report examined the feasibility of such fabrication technique and the resultant microstructure. It was found that Al3Ni forms when molten aluminium comes in contact with powder preform but fails to form any other intermetallic phase such as Al3Ni2 as predicted by AI-Ni phase diagram for the Al and Ni concentrations used in this investigation. This has been attributed to an incubation period for initiating exothermic reaction, which allowed molten aluminium to infiltrate and thus bring the stoichiometry to that of Al3Ni. (C) 2001 Elsevier Science B.V. All rights reserved.