Growth of γ′ precipitates in nickel-base superalloy

Abstract

The growth behaviour of γ′ (L12)-phase precipitates in Inconel X-750 type Ni-base alloy has been investigated mainly by micro-Vickers hardness test and transmission electron microscopy. The precipitating phase was observed to be spherical especially at the early stage of aging time and to be ordered fcc γ′ phase, likely pointed out previously. The hardness of specimens aged in various conditions closely related to the size of γ′ precipitates. The growth kinetics of γ′ precipitates followed the predictions of Lifshitz-Slyozov-Wagner (LSW) theory of diffusion controlled growth at all aging temperatures. The activation energy for the growth of γ′ precipitates was estimated to be 281 kJ/mol which was nearly similar to those of diffusion of solute atoms in Ni and Ni-base alloys. This would also suggest that the growth of γ′ in Inconel X-750 type alloy follows the Ostwald ripening of diffusion-controlled growth. The actual particle size distribution of γ′ was somewhat different from the distribution predicted by the LSW theory.