Characterization of the Initial Stages of Dynamic Recrystallization in ATI 718Plus®

Abstract

ATI 718Plus® is a polycrystalline multi-phase strengthened Ni-base superalloy suitable for turbine disc applications in aero engines. A typical turbine disc experiences temperatures in the rim up to 650–700 \(^{\circ }\)C and stresses as high as 1000 MPa in the cooler parts of the component. The manufacturing process, especially forging and heat treatment, plays a pivotal role in achieving the final microstructure and associated mechanical properties needed to withstand this harsh environment. The microstructural evolution during aforementioned processes is directly related to dynamic recrystallization. The changes occurring during the initial stages of deformation are of particular interest as partially recrystallized areas with a broad range of grain size can be detrimental for the mechanical properties of the component. ATI 718Plus® has been used in this work to study grain nucleation and growth during recrystallization. To evaluate the importance of the deformation conditions on the outcome of the forging, a set of specimens were produced from a single billet of ATI 718Plus®. Hot compression tests were performed on Rastegaev-samples across a wide range of temperatures, strains and strain rates. In addition, the characteristics for meta-dynamic recrystallization were evaluated on a samples subset. The evolution of the flow curves as well as the development of the microstructure will be presented. This study specifically focuses on the role of deformation parameters as well as their influence on the recrystallized fraction and grain boundary misorientation angle.