Microstructure Quantification in Nickel-Based Superalloy Udimet 720Li

The morphology of gamma' A precipitates for the wrought Ni-based superalloy Udimet 720Li was quantitatively evaluated by applying the absolute moment invariant technique. The diameter of the secondary gamma' A precipitates, d, increased continuously with the decrease of the cooling rate, v, after solution treatment at 1473 K for 1 h along the following equation; d proportional to v(-0.4). In addition, with decreasing cooling rate, the shape of the secondary gamma' A precipitates changed from spherical to octodendritic. For the oil-quenched alloy after solution treatment, d continuously increased with the increase of the aging time at 1173 K, and the spherical shape remained unchanged during the process. On the contrary, for the furnace-cooled alloy, the shape evolved from octodendritic to spherical with the aging time, exhibiting an almost constant d.