HREM INVESTIGATION OF HOMOGENEOUS DECOMPOSITION IN A NI-12 AT-PERCENT AL-ALLOY

Using HREM gamma'-precipitates in NiAl of radii down to 0.7 nm are imaged. This enables us to see undercritical nuclei and to observe the nucleation process in a Ni-12 at.% Al alloy. The kinetics of decomposition of this alloy ay 773 K was followed. The time dependence of the precipitates' size distribution, their volume density, their mean radii and the volume fraction of the gamma'-precipitates were measured on HREM micrographes. The results are compared quantitatively with classical nucleation theory and with the LSW-theory for Ostwald-ripening.