Constitutive Characterization and Microstructure Evolution of As-extruded FGH4113A Superalloy with Ultrafine Grain During Isothermal Forging
Forging is the key forming process for producing advanced aero-engine powder turbine disks.The microstructure of as-extruded alloy mostly depends on the chemical composition of alloy and extrusion processing parameters.The average grain size number is greater than 13 for the novel powder nickel-based superalloy FGH4113A after hot extrusion,and the as-extruded alloy has dual-phase microstructure of γ+γ'.The fine and homogeneous dual-phase microstructure makes it possible to broaden isothermal forging processing window.In this study,Gleeble hot compression experiments for as-extruded FGH4113A alloy with ultrafine grains were carried out at temperatures of 1000,1040,1080,1120 ℃ and strain rates of 0.001,0.01,0.1 s-1.Height reduction was 60％for samples under all experiment conditions.The results show that no crack is found on the surface of alloy samples under all experiment conditions,suggesting that the as-extruded FGH4113A alloy with ultrafine grains has a wide isothermal forging process window.The average activation energy for the alloy is 515.375 kJ/mol.True stress-true strain curves show a steady flow characteristic for samples under low strain rate(0.001 s-1)and the change from work hardening to recrystallization softening for the samples under high strain rate(0.1 s-1).γ'is sensitive to temperature,and recrystallization grains grow obviously at high deformation temperature due to the dissolution of a large amount of γ'.Furthermore,the main recrystallization way is discontinuous dynamic recrystallization for as-extruded FGH4113A alloy with ultrafine grains.This study offers experiment evidence for forging processing design of the as-extruded FGH4113A alloy with ultrafine grains.
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