ANALYSIS OF INSITU FORMATION OF TITANIUM CARBIDE IN ALUMINUM-ALLOYS

A novel technique to generate fine single-crystal TiC platelets in an Al-4.4wt.%Cu matrix has been developed. The highly exothermic process is moderated by means of a carrier gas and leads to a fine (0.1-2.0-mu-m) and homogeneous distribution of the stoichiometric carbides. An analysis is provided to examine the carbonaceous gas decomposition reaction, the reaction products and reaction paths, the rate-limiting steps in the formation of TiC and the solidification route from analytical and experimental evidence it is suggested that nucleation of the carbide occurs via titanium diffusing to the carbon and precipitating out as a carbide via a solid-liquid chemical reaction. In the initial stage of the process, the rate-limiting step is the supply of carbon in the carrier gas. Towards the latter part of the process, with titanium depletion, diffusion of titanium across the boundary layer is the rate-limiting step. Theoretical thermodynamic considerations indicate that TiC is stable during solidification and Al4C3 formation is precluded.