In-Situ HT-EBSD Measurements and Calibration of Multi-class Model for Grain Growth and δ-phase Dissolution Kinetics of Alloy 718

Abstract

In the aerospace industry the microstructure evolutionMicrostructure evolution of alloy 718Alloy 718 during forgingForging and heat treatmentHeat treatment and the resulting mechanical propertiesMechanical properties are decisive in view of the high-quality requirements of aircraft components. During thermomechanical processing the temperature control and adiabatic heating lead to grain growth and, if δ-solvus temperature is exceeded, to the dissolution of the δ-phase, which further results in accelerated grain growth. To describe the history of the microstructureMicrostructures in terms of grain sizeGrain size during and after forgingForging or heat treatmentHeat treatment an existing multi-class microstructureMicrostructures model is optimized with a focus on grain growth kineticsGrain growth kinetics and parameterized by experimental results. The multi-class model describes the microstructureMicrostructures and the coarsening during processing more precisely in terms of the grain sizeGrain size distribution than previously used single-class models. A topic for other but related work is the prediction of mechanical propertiesMechanical properties such as tensile strength, fracture toughnessFracture toughness and creepCreep resistance, which requires a precise prediction of grain sizeGrain size characteristics in terms of sizes and size distributions as provided by the model presented in this work. The experimental data basis stems from in-situ high-temperature electron backscatter diffraction (HT-EBSD) investigations and supporting experiments. The experimental setup and the results are discussed in detail.