Microstructure evolution of ATI718 plus alloy during high-speed machining: Experiments and a combined FE-CA approach

Abstract

Excellent surface integrity is an eternal pursuit in high performance manufacturing, with microstructure being a crucial component of the surface integrity dataset and a key factor controlling surface properties such as fatigue and creep. The multi-physical fields generated by thermo-mechanical loads during high-speed machining act on the processed surface layer, influencing the evolution of microstructures. To investigate the microstructural evolution mechanisms of ATI718 plus during high-speed machining, cutting experiments and techniques such as Electron back scatter diffraction (EBSD), Transmission Kikuchi diffraction (TKD), and Precession electron diffraction (PED) is conducted to quantitatively analyze the microstructures in the chip shear zone and the machined surface. Subsequently, a combined finite element (FE) and cellular automata (CA) model is developed to simulate the microstructure evolution during the cutting process. The discontinuous dynamic recrystallization (DDRX) mechanism is employed to demonstrate the nucleation and growth of grains under the influence of multiple physical fields. The simulation and experimental results show similar dynamic recrystallization (DRX) grain sizes, indicating acceptable accuracy of the CA model in terms of DRX grain size. The comparison between experimental and simulation results confirms the occurrence of both continuous dynamic recrystallization (CDRX) and DDRX during the cutting process. The synergistic competition between CDRX induced grain lamellar refinement and DDRX induced grain growth emerge as the primary mechanism driving microstructural evolution. A layer of ultrafine grains, with a thickness within 20 μm, is formed on the machined surface. Results under different parameters demonstrate that the temperature has a more significant impact on the thickness of the ultrafine grain layer and the diameter of grains within the layer compared to the strain rate.