Microstructure Quantification in Wrought Ni-Based Superalloy Udimet 720Li

Abstract

The morphology of γ′ precipitates was quantitatively evaluated for wrought Ni-based superalloy Udimet 720Li by using the absolute moment invariant technique. The diameter of secondary γ′ precipitates, d, increases continuously with the decrease of cooling rate, v, after the solution treatment at 1473 K/1 h along the following equation; d ∝ v^-0.4. It is found that the secondary γ′ precipitates changes from spherical to octo-dendrite in shape with the decrease of cooling rate. In the case of oil-quenched alloy after the solution treatment, the value of d continuously increases with aging time at 1173 K, while the spherical shape remains unchanged during aging. On the contrary, for the furnace-cooled alloy, the shape of secondary γ′ precipitates evolves from octo-dendrite to spherical in shape with aging time under the almost constant value of d.