Evolution of γ′ morphology and γ/γ′ lattice parameter misfit in a nickel-based superalloy during non-equilibrium cooling

Abstract The change of γ′ phase morphology in quenched Ni-based superalloy strengthened by γ′ precipitates was investigated by means of scanning electron microscopy and X-ray diffraction. Lattice parameters of γ and γ′ phases and subsequently the δ parameter were calculated. Relatively high content of gamma prime formers resulted in a substantially high volume fraction of precipitates in the dendrite cores. The volume fraction of γ′ phase was significantly decreased due to dissolution of precipitates in the surrounding matrix, as a result of short-term subsolidus exposure. The lattice parameter of γ′ phase was higher than that of γ phase, which results in a positive δ parameter in fully heat treated (FHT) and also FHT+ Quench conditions. For (200) and (220) reflections the γ/γ′ misfit was lower in the FHT + Q sample.