Surface microstructure evolution analysis of Inconel 718 during ultrasonic vibration-assisted grinding using FEM

Abstract

In this study, a novel method for predicting microstructure evolution through secondary post-processing of finite element method (FEM) simulation results is proposed. This developed method integrates grinding process variables (strain ε, strain rate $\dot{\epsilon }$, temperature T, stress σ, etc.) with the unified constitutive equations of Inconel 718 to calculate the distribution of normalized dislocation density $\overline{\rho }$, recrystallization volume fraction S, and grain size d at any frame time. Furthermore, the microstructure evolution during ultrasonic vibration-assisted grinding (UVAG) was analyzed under varying ultrasonic vibrations A, spindle speeds n, and grinding depths a_p. The research results indicate that the microstructure evolution mainly divided into three stages, resulting in the formation of refined grain region and high-density dislocation region in the ground surface layer. Ultrasonic vibration increases the depth of the refined grain region and the dislocation density in the ground surface layer, due to the strain increases and temperature decreases caused by periodic vibration. Additionally, increases in spindle speed and grinding depth leads to higher dislocation density, recrystallization fraction, and refine grain depth. The microstructures (dislocation density, depth of refine grain region) in the ground surface layer were characterized via transmission electron microscopy (TEM) and electron back scattered diffraction (EBSD), and the experimental results verified the effectiveness of the developed method for predicting microstructure evolution. This method provides a new approach for understanding and controlling the microstructure evolution of the grinding surface of Inconel 718 during the UVAG process.