EXPERIMENTAL-STUDY AND NUMERICAL-SIMULATI ON OF THE KINETICS OF GAMMA' PRECIPITATION AND MICROSTRUCTURAL EVOLUTION IN AN N18 SUPERALLOY DURING QUENCHING

The high temperatures and stresses experienced within turbine discs re quire high temperature resistant Ni-base superalloys produced by Powde r Metallurgy techniques. The alloy N18 we study has good overall mecha nical properties at temperatures up to 700 degrees C after appropriate heat treatment. These properties are derived from the precipitation o f ordered gamma' phase and are strongly dependent upon the microstruct ure produced during thermal treatments. The gamma' precipitation kinet ics is experimentally studied by dilatometry and transmission electron microscopy. The microstructural evolution of gamma' precipitates duri ng quenching is followed in a high quenching rate apparatus that permi ts to preserve the high temperature microstructure at room temperature . In the present work, a model is being developped and is experimental ly verified in order to describe the intragranular gamma' precipitatio n during quenching.