Peritecticlike precipitation of titanium carbide in Al-Ti-C melts at 1373 K

The reaction between an Al-Ti melt and a carbon containing medium, i.e. pur e graphite or molten aluminium containing aluminium cal bide, was studied. Experiments were carried out at 1373 K, using three different experimental setups. Depending on the carbon source, titanium carbide precipitated as a layer or as free particles. Classical nucleation theory for homogeneous and heterogeneous nucleation is used to assess the surface tension. The influe nce of stoichiometry on surface tension and nucleation is discussed. The fo rmation of a continuous layer or peritecticlike precipitation of titanium c arbide, is theoretically analysed. The growth of the layer is rate controll ed by the mass transfer of carbon at the interface, plausibly as a result o f the ordering tendencies in titanium carbide. The degeneration of precipit ation into that of freely formed particles is found to be nucleation contro lled. A model for degenerate precipitation is proposed, including predictio ns of the reaction front compositions, growth rate, and particle fractions in a dilute ternary system. The model is in good agreement with experiments , after compensating for settling of the precipitates, except in predicting the precipitated functions. MST/3830