Multimodal size distributions of γ′ precipitates during continuous cooling of UDIMET 720 Li

The technological properties of many nickel-based superalloys originate in the morphology and distribution of Ni3(Al, Ti) particles (γ′ precipitates). Starting from the solution-annealed condition, the distribution and the morphology of γ′ precipitates are investigated experimentally during continuous cooling of the nickel-base superalloy UDIMET 720 Li. Characterization of the precipitates is carried out by scanning electron microscopy and energy-filtered transmission electron microscopy investigations. Depending on cooling rate, monomodal, bimodal and even trimodal size distributions are observed. The experimental observations of the size distributions are confirmed by numerical simulations of the γ′ precipitation kinetics. The theoretical background for occurrence of multimodal size distributions during continuous cooling is discussed.