Growth accidents induced by primary γ′ precipitates in a polycrystalline nickel-based superalloy

Abstract

The development of overgrown grains during sub-solvus annealing of a polycrystalline γ−γ′ nickel-base alloy is investigated, with special emphasis on the primary γ′ precipitates. Quantitative analysis conducted on a large three-dimensional electron back-scattered diffraction dataset reveals a high fraction of γ′ precipitates on the annealing twin boundaries in the large grains. When observed in-situ in a scanning electron microscope, the formation of annealing twins is correlated to the crossing of γ′ precipitates by moving grain boundaries. The role of precipitates in the occurrence of growth accidents is discussed.