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

In the aerospace industry the microstructure evolution of alloy 718 during forging and heat treatment and the resulting mechanical 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 microstructure in terms of grain size during and after forging or heat treatment an existing multi-class microstructure model is optimized with a focus on grain growth kinetics and parameterized by experimental results. The multi-class model describes the microstructure and the coarsening during processing more precisely in terms of the grain size distribution than previously used single-class models. A topic for other but related work is the prediction of mechanical properties such as tensile strength, fracture toughness and creep resistance, which requires a precise prediction of grain 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.