A Study on Microstructural Evolution in Cold Rotary Forged Nickel-Superalloys: C263 and Inconel 718

Abstract

C263 and Inconel 718 are precipitation hardenable nickel-superalloys widely used in different sections of a gas turbine engine dependent on their strength and temperature capability. Cold rotary forging is an effective route for manufacturing axisymmetric components with significantly higher material utilisation as compared to machining from conventional hot forgings. This paper presents a study on how C263, an alloy system strengthened by γ’, and Inconel 718, an alloy system strengthened by γ” and δ, deform during the cold rotary forging process and how their microstructures evolve. The two alloys exhibit maximum formability in solution-annealed condition. In this study, both C263 and Inconel 718 were annealed before the cold rotary forging operation. Parts with a 90° bend flange were successfully cold rotary forged from tubular preforms with a wall thickness of 6 mm. For both the alloys, the cold rotary forged parts exhibit significant differences in material properties from the undeformed sections to the most deformed section (i.e. the flanges). Post-forging heat-treatments are required to impart the desired material properties throughout the part. Therefore, appropriate annealing and aging treatments were identified for each of the two alloys. These heat-treatments led to uniform material properties for both deformed and undeformed sections of the cold rotary forged flanges in case of both the alloys.