Microstructural homogeneity and hot-workability enhancement of Inconel 718 by tailoring intragranular Ni–Nb-based precipitates

The effect of intragranular Ni–Nb-based precipitates on the microstructural evolution and hot workability of Inconel 718 was systematically investigated. Three heat-treatment routes were designed to control the spatial distribution and phase constitution of Ni–Nb-based precipitates: homogenized (Ho), delta-processed (DP; grain-boundary δ), and pre-aging-treatment-assisted delta processing (PAT–DP; introducing intragranular δ via γ″ precipitation and subsequent transformation). Hot compression tests were conducted at temperatures of 900–1150 ℃ and strain rates of 0.01–10 s -1 to a true strain of 1.0. The results revealed that the spatial distribution of Ni–Nb-based precipitates governs the dominant DRX nucleation mode, shifting it from grain-boundary-dominated to intragranularly assisted nucleation. Compared with Ho and DP, PAT–DP exhibited higher initial work hardening and peak stresses (by up to 13.1%), attributed to the combined dislocation-pinning effect of intragranular γ″ and δ precipitates. More importantly, the mixed intragranular distribution of γ″ and δ precipitates promoted more homogeneous DRX nucleation within grain interiors, resulting in a higher recrystallized fraction and reduced grain-size dispersion. Processing map analysis, combined with crack susceptibility index evaluation, confirmed that PAT–DP provides a wider processing window and lower crack susceptibility. These results suggest that tailoring the intragranular distribution of Ni–Nb-based precipitates enables the simultaneous improvement in microstructural homogeneity and hot workability, offering a robust strategy for process optimization in Inconel 718.