Mechanical processing and microstructural control in hot working of hot isostatically pressed P/M IN-100 superalloy

The hot deformation behavior of hot isostatically pressed (HIPd) P/M IN-100 superalloy has been studied in the temperature range 1000–1200°C and strain rate range 0.0003–10 s −1, using hot compression testing. A processing map has been developed on the basis of these data and using the principles of dynamic materials modelling. The map exhibited three domains: one at 1050°C and 0.01 s −1, with a peak efficiency of power dissipation of ≈32%, the second at 1150°C and 10 s −1, with a peak efficiency of ≈36% and the third at 1200°C and 0.1 s −1, with a similar efficiency. On the basis of optical and electron microscopic observations, the first domain was interpreted to represent dynamic recovery of the γ phase, the second domain represents dynamic recrystallization (DRX) of γ in the presence of softer γ′, while the third domain represents DRX of the γ phase only. The γ′ phase is stable upto 1150°C, gets deformed below this temperature and the chunky γ′ accumulates dislocations, which at larger strains cause cracking of this phase. At temperatures lower than 1080°C and strain rates higher than 0.1 s −1, the material exhibits flow instability, manifested in the form of adiabatic shear bands. The material may be subjected to mechanical processing without cracking or instabilities at 1200°C and 0.1 s −1, which are the conditions for DRX of the γ phase.