Influence of as-cast and forged states on constitutive behavior and hot processing maps of INCONEL 783 superalloy

Inconel 718 or GH6783, a critical nickel-based superalloy for key components in advanced aircraft engines, presents significant manufacturing challenges due to its inherently poor workability and narrow thermomechanical processing window, demanding innovative approaches for precise and defect-free fabrication. The constitutive behavior and hot work processing map of both as-cast and forged IN-783 alloy are studied at different temperatures and strain rates. The forged IN-783 alloy demonstrates greater resistance to flow instability, particularly at temperatures above 1100 °C, accompanied by higher peak power-dissipation efficiency (40 %–45 %) compared to the as-cast state (35 %–38 %). The established Zener-Hollomon constitutive equations relates flow strength σ (MPa) and T (K) and strain rate $\dot{\epsilon }$ (s⁻¹) for as-cast state is

$\sigma =172.85\ln \left[{\left(\frac{Z}{2.91\times {10}^{17}}\right)}^{\frac{1}{3.93}}+\sqrt{1+{\left(\frac{Z}{2.91\times {10}^{17}}\right)}^{\frac{2}{3.93}}}\right]$, $Z=\dot{\epsilon }{e}^{\frac{57363.5}{T}}$,

whereas that for forged state is.

$\sigma =167.5\ln \left[{\left(\frac{Z}{1.98\times {10}^{20}}\right)}^{\frac{1}{4.15}}+\sqrt{1+{\left(\frac{Z}{1.98\times {10}^{20}}\right)}^{\frac{2}{4.15}}}\right]$, $Z=\dot{\epsilon }{e}^{\frac{66942.5}{T}}$.

Based on hot processing maps, preliminary breakdown deformation for as-cast alloy, should be conducted at lower strain rates ∼0.1 s⁻¹ near 1050 °C, followed by a finishing pass at approximately 1050 °C and lower strain rate ∼0.05 s⁻¹. The recommended processing conditions for forged IN-783 alloy are deformation at 1080–1120 °C and 0.3–0.6 s⁻¹. The forged IN-783 alloy exhibits superior thermal stability with a higher activation energy (556.6 kJ/mol vs. 476.9 kJ/mol), extended safe-processing temperature range (50–70 °C higher), and broader strain-rate window (approximately threefold) compared to the as-cast counterpart. Based on constitutive and processing map analyses, optimized thermomechanical parameters are proposed to facilitate industrial hot-working processes.