PRECIPITATION AND GROWTH OF GAMMA' AND GAMMA'' PHASES IN A 41.5NI-40FE-16CR-2.9NB-1.8TI-0.2AL ALLOY

A 41.5Ni-40Fe-16Cr-2.9Nb-1.8Ti-0.2Al alloy is a superalloy strengthene d by the precipitation of gamma' and gamma '' phases. The knowledge of the nucleation and growth behaviors of the gamma' and gamma '' precip itates is very important for a appropriate usage of the alloy. We inve stigated the precipitation characteristics of this alloy by micro-Vick ers hardness test, X-ray diffraction and transmission electron microsc opy. The hardness of the alloy aged in various conditions closely rela ted to the size of the gamma' and gamma '' precipitates. With increasi ng aging time, the lattice parameter of the alloy matrix decreases and reaches a constant value at each aging temperature after a certain ag ing lime. The volume fractions of gamma' and gamma '' phases precipita ted in the alloy at 993K are 7.2% and 13.3%, respectively. The growth kinetics of the gamma' and gamma '' precipitates followed the predicti ons of LSW theory of diffusion controlled growth at all aging temperat ures. The activation energy values for the growth of gamma' and gamma '' precipitates are estimated to be 278 kJ/mol and 431 kJ/mol, respect ively. Some gamma '' precipitates contain gamma' precipitates inside t heir bodies or are in contact with the gamma' precipitates. It is cons idered that some gamma' precipitates of this allay act as preferential nucleation sites for the gamma '' precipitates.