Multimodal distribution of g′ phase and effect on hot deformation in a wrought nickel base superalloy

Abstract:

The microstructural evolution of different generations of ?′ precipitates during various heat treatment processes of a nickel base superalloy has been investigated. After solutionizing in the single ? phase field, continuous cooling, interrupted cooling and isothermal annealing tests were performed and characterization of the precipitates was carried out by scanning electron microscopy. It is found that a monomodal size distribution of the secondary ?′ precipitates can be achieved at a very high cooling rate in the continuous cooling process. With the decrease of the cooling rate, the secondary ?′ precipitates grow gradually and gather together to form a flowery morphology. When the secondary supersaturation is developed in the vicinity of the secondary ?′ precipitates during isothermal annealing, the water-quenched tertiary ?′ precipitates are produced and result in a bimodal size distribution of ?′ precipitates with the larger secondary precipitates. Furthermore, the effects of the secondary ?′ particle growth on the hot deformation are also discussed.