Coarsening of γ′-precipitates in single-crystal superalloy SRR 99

Abstract

Coarsening of l'-precipitates in single-crystal superalloy SRR 99The effects of isothermal annealing between 800 and 1200°C on the microstructure of single-crystal SRR 99 have been investigated. During aging at either 800 or 900°C, the precipitates adopt an irregular, rounded, and highly interconnected array which suggests that they have undergone coalescence. Aging at higher temperatures was found to produce a regular cuboidal precipitate morphology, although long-term aging promoted the formation of "1'-'rafts '. The precipitate size distributions were found to be broader than those predicted by the Lijshitz-Slyosov and Wagner theory, and the coarsening kinetics also showed significant deviations from the power law prediction of this theory. The reasons for these deviations are discussed in the light of the available models, and it is suggested that a progressive transition in the dominant coarsening mechanism takes place.

In situsmall-angle neutron scattering investigation of the γ′ precipitation and growth in the nickel-based single-crystal alloy SC16

“…Up to now there are very few works monitoring in situ the nucleation and growth of the γ phase in technical alloys such as SC16. Hopgood and Martin [11] observed the coarsening of γ in the alloy SRR 99 as a function of the ageing time at fixed temperatures by means of transmission electron microscopy (TEM). Royer et al [12] investigated by scanning electron microscopy (SEM) and TEM the change in morphology during the rafting of the particles in the AM1 superalloy, but still starting from room temperature (RT) and approaching the solvus temperature from below.…”