This investigation explores nucleation and growth of precipitates through the concept of ledge mechanisms. The formation rate of growth ledges on the face-centered cubic/body- centered cubic interphase boundaries of facetted precipitates is measured in nickel-chromium alloys by hot stage transmission electron microscopy. Ledge formation rates predicted from classical nucleation theory are compared to those measured experimentally. The contributions of solute supersaturation, strain energy, and interphase boundary energy to ledge nucleation are assessed. The role of misfit dislocations at interphase precipitate/matrix boundaries during growth is determined. These results should provide a connection between the geometric approach to explaining precipitate shape employed by the invariant line model and the physical mechanism of precipitate growth.
