Small-scale Experiments on the Recrystallization of alloy 718 and their Transferability to Industrial Production

Abstract

The precise control of grain size during hot deformation is paramount for the mechanical integrity of aerospace-grade nickel-base superalloys. This study investigates the recrystallization behavior of Nickel-base alloy 718 by employing classical hot deformation experiments in combination with a novel experimental setup: a DSI Gleeble 3800 thermal-mechanical simulator integrated with a Laser Ultrasound system. This approach allows for the in-situ measurement of microstructural changes — specifically grain growth and recrystallization — during the actual deformation and following heat treatment. Isothermal compression tests were conducted at different temperatures, partly with subsequent holding at temperature. The Laser Ultrasound system utilizes a pulsed laser to generate ultrasonic waves and a laser interferometer to detect them. By measuring the ultrasonic attenuation in real-time, the recrystallization and grain growth was quantified as it occurred. Results indicate that hot deformation with Laser Ultrasound provides a very good correlation with post-mortem EBSD (Electron Backscatter Diffraction) analysis, particularly in identifying the necessary temperatures and holding times required for meta-dynamic recrystallization. This approach supports the optimization of thermomechanical processing routes for nickel base superalloys used in aerospace applications.