Dislocation-controlled precipitation of TiC particles and their resistance to coarsening

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Abstract
The formation of TiC precipitates in an austenitic steel has been investigated by transmission electron microscopy. By nucleation at pre-existing dislocation networks high densities of finely dispersed TiC precipitates were created (4–15 nm average particle diameter), while precipitation in a dislocation-free matrix was found to be completely inhibited. TiC precipitation at stacking faults and grain boundaries was found to be also strongly influenced by the dislocations and their interaction with planar defects. Investigation of precipitate growth as a function of time and temperature showed that in the range 600–900°C the TiC precipitates are extremely stable against coarsening. This result is of great importance for elevated temperature applications of the material. Present growth and coarsening theories do not account for the observed temperature and time dependence of the precipitate growth. A growth mechanism is proposed which is based on solute sweeping during dislocation recovery and enhancement of local supersaturation of solute due to dislocation reactions.