Modeling Transient Temperature-Driven Microstructure Evolution in Inconel 718 during Hot Forming

Diffusion and defect data, solid state data. Part B, Solid state phenomena/Solid state phenomena, vol. 390, pp. 85–96

Abstract

Industrial hot forming of nickel-based superalloys is typically carried out under non-isothermal conditions, where rapid temperature changes between forming steps not only affect the thermo-mechanical response but also the microstructural evolution, including processes such as recrystallization. Most microstructure models are developed and calibrated for idealized isothermal conditions, and their applicability to realistic transient temperature paths is still unclear. Therefore, this study investigates the microstructure evolution of Inconel 718 under non-isothermal hot deformation by combining dilatometer tests with full-field simulations using DIGIMU® in order to provide detailed insight into the underlying microstructural mechanisms and to assess the capability of a Full-Field approach for modelling such non-isothermal forming conditions. For this aim, compression tests with temperature increases (1020 °C to 1070 °C) and decreases (1120 °C to 1070 °C) were performed, with the temperature change applied at different strains. The results reveal a path dependence, heating at low strain to 1070 °C leads to higher DRX-fractions and finer, more homogeneous grain structures, whereas later heating at higher strains produces coarser, partially recrystallized microstructures due to reduced strain at the higher temperature. For the temperature decrease, DRX occurs predominantly at 1120 °C, after a late temperature change, no additional DRX takes place at 1070 °C. While an earlier change still allows additional DRX. The Full-Field simulations reproduce these trends in dislocation density, recrystallized fraction and grain size distributions with good qualitative agreement and moderate quantitative deviations. Overall, the study demonstrates that the timing and direction of temperature changes affect the final microstructural state, and that DIGIMU®, a Full-Field approach, can capture path-dependent microstructure evolution in Inconel 718 and provides a useful digital tool for analyzing and designing transient temperature hot forming processes.

Authors 4

1. Nadine Mostafa Talaat Elekyabi Aachen

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen University

2. Holger Brüggemann Aachen

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen University

3. Emad Scharifi Aachen

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen University

4. Junhe Lian Aachen

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen University