Precipitate growth activation energy requirements in the duplex size γ′ distribution in the superalloy IN738LC

Abstract

The precipitate growth features in the duplex size (fine and coarse) precipitate distribution, obtained by quenching the alloy from the holding temperature of 1140°C, was studied by treating the alloy for various times in vacuum at selected temperatures in the range 800–1100°C. It was found that both the fine and the coarse precipitate particles grow with time, apparently aided by the particle movement in the matrix and coalescence, by the so-designated Precipitate Agglomeration Mechanism (PAM). At 1100°C the fine particles grew to the size of the coarse particles in about 100 hours and a near single coarse size of about 840 nm was obtained in the matrix. The activation energies for the growth of both the fine and coarse particles were calculated using particle sizes at different temperatures after 25 h of aging and at 1040 and 1100°C for different aging times. These were found to decrease continuously with an increase in size of the particles, meaning that the coarse particles grow more easily than the fine particles, requiring less activation energies. This behavior could be attributed to the greater attractive force with which the coarser particles would attract the finer particles.