The influence of cooling rate from temperatures above the γ′ solvus on morphology, mismatch and hardness in advanced polycrystalline nickel-base superalloys

The interrelationships between composition, γ′ morphology, hardness and γ-γ′ mismatch were identified for a set of advanced nickel-base polycrystalline superalloys. When cooling from a temperature above the γ′ solvus, i.e. a supersaturated γ matrix, it was found that the cooling rate determines the γ′ morphology and particle distribution that develops. This in turn dictates the hardness of the alloy system and the mismatch in lattice parameters between the γ and γ′ phases. This work shows that the development of these parameters is relatively insensitive to alloy composition. Moreover, the thermal history, especially cooling rate through the γ′ solvus temperature is found to be the critical factor in determining alloy response.