Mechanism of TiC formation in Al/TiCin situ metal-matrix composites

Abstract

In recent years, metal-matrix composite (MMC) processing techniques have evolved, whereby the reinforcing particulates are formed in situ in a molten alloy, and the melt containing the dispersions is cast into an ingot for subsequent fabrication into wrought products. One such approach involves the formation of TiC particulates in aluminum alloy matrices via a gas-molten metal reaction. In this approach, a carbon-bearing gas is introduced into a molten Al-Ti alloy, allowing Ti in the melt to react with the carbon released from the injected gas to form TiC. The volume fraction and the size of TiC particles are important parameters which influence the mechanical properties of these composites. Although it is reasonably clear that the volume fraction of the TiC particles is basically determined by the initial content of the Ti content of the melt, given a continuous supply of carbon during processing, the mechanisms responsible for controlling the TiC particle size are unclear. This communication is intended to present some recent results which provide some insight into the formation mechanisms.