Abstract:Samples, made of Ti-6Al-2C alloy through casting, were held at 1300℃ for a relatively long period and their coarse primary grain became granular, which may contribute to the mechanical properties of the alloy. The mechanism of the granulation of primary dendritic TiC was studied by means of XRD, SEM and TEM. The results show that the granulation is carried out through the process of dissolution, diffusion and precipitation of carbon, and the dominant step is diffusion. The equilibrium compositions are different at the points with different curvatures according to Gibbs-Thomson effect. This equilibrium is broken down by the diffusion of carbon at high temperatures, which makes the TiC dissolve at the point with high degree of curvature and precipitate at the point with low degree of curvature. Eventually, the dendrite is molten completely at the point with high degree of curvature so that it becomes several granular grains.

Key words: Ti alloy; composite; mechanism of granulation; high temperature heat treatment