Effect of cooling rate on the morphology of γ′ precipitates in a nickel–base superalloy under directional solidification

Abstract

The morphological evolution of γ′ precipitates in a nickel-based superalloy K5 was studied by zone melting directional solidification under vacuum conditions. The results show that at the lower cooling rate of 12.42 K s^–1, γ′ precipitates remand big cuboids, γ′ particles become smaller at the cooling rate ranges from 12.42 to 38.80 K s^–1. For a rather fast cooling rate of 50.16 K s^–1, γ′ particles retain a spherical shape. The experiments show that big cuboids will become unstable and split into several small one at the lower cooling rate of 1.1 K s^–1. The mechanism of the evolution of the γ′ morphologies is also analyzed by introducing a new parameter-shape factor which classifie the total energy into several energy levels. Based on this, the effect of the cooling rate on the γ′ morphology is discussed.

Key words:

• Superalloy
• γ′ Morphology
• Cooling rate