From lab to disk forging: Validating superplasticity in microstructure-optimized PM nickel-based superalloy via in situ DIC and small-scale sample modeling

The superplastic forming of difficult-to-deform powder metallurgy (PM) Ni-based superalloys is crucial for their industrial application. This study achieved the superplastic forming of a PM Ni-based superalloy, GX001, through microstructural optimization using a sub-solvus heat treatment with slow cooling, which coarsened incoherent γ′ precipitates and effectively enhanced the alloy's formability. It also employed precise constitutive modeling using an in situ digital image correlation method to monitor deformation in real-time to predict the optimal deformation conditions. The constitutive modeling reveals that the optimal superplasticity regimes are near the conditions of 980 °C/0.001s −1 and 1080 °C/0.001s −1 . They are also evidenced by the tensile and compression tests, which show an elongation of 341 % at 1080 °C/0.001s −1 and a reduction of 75 % without cracking during compression at 980 °C/0.001s −1 , respectively. Furthermore, the microstructural characterization revealed the origin of the superplasticit: (1) besides the DRX from grain boundary, heterogeneous dynamic recrystallization triggered by primary coarsened γ′ precipitates, yielding the accumulation of dislocations; (2) participation of the γ transformed from γ′ dissolution in deformation, accommodating dislocations via the formation of dislocation cells and walls; and (3) microstructure stabilized through the pinning effect on grain boundary provided by incoherent dissolving γ′ particles and MC carbides. Finally, the novel modeling method, microstructural optimization, and the superplasticity mechanism proposed in this study are believed to be significant for forming difficult-to-deform PM superalloys, as further proven by a successfully forged industrial-scale disk. It should be mentioned that the present method for predicting the deformation behavior of a large-scale sample should consider its size effect. • Slow cooling process yields coarsened γ′ precipitates, enhancing formability. • Hot processing maps‌ predict dual optimal processing windows. • KAM analysis‌ reveals γ′ phase actively deforms during compression. • Superplasticity occurred through transformed γ from γ′, coarsened γ′, and DRX. ‌. • Superplasticity is achieved at 1080 °C/0.001s −1 , enabling industrial forging.