Akaash Chakkaravarthy

• Ultrasonic processes are typically energy time and cost efficient and recently of high interest, especially for joining. However, the sonication of materials is often associated with phenomena that remain largely unresolved to date, such as increased ductility during sonication and microstructural changes. To gain a deeper understanding of the elementary processes contributing to increased ductility through ultrasonic sonication, this study investigates the modification of metal by ultrasound and its impact on the density of geometrically necessary dislocations (GNDs). The presence of a large grain structure in IN617 allowed the effect of ultrasound to be more easily observed and analysed. Therefore, samples of IN617 were used for study. The effect of ultrasonic treatment on the density of GNDs in IN617 was analysed using Electron Backscatter Diffraction (EBSD) measurements. Additionally, an E–m model and finite element modelling (FEM) were employed to gain deeper insights into grain behaviour. The FEM model was successfully applied by correlating the mechanical behaviour predicted by the E–m model based on Young’s modulus and the Schmid factor with experimental observations. A combination of experimental data and computational modelling was used to analyse the effect of ultrasonic treatment on dislocation dynamics. EBSD data from three different samples were used to simulate the material’s response to various mechanical and ultrasonic loading conditions. The analysis revealed distinct variations in GND density across the samples. Many grains exhibited a unique response under different loading conditions, as observed through Young’s modulus, Schmid factor, resolved shear stress, and plastic strain. The results indicate that ultrasonic treatment influences dislocation behaviour by either promoting stress relaxation or increasing local hardness. A geometrically necessary dislocation (GND) analysis was conducted to explore the effect of plastic deformation on three different samples (N1, N2, and N3) of IN617 alloy after sonication was applied. Several software tools, including MATLAB, MTEX tool box, Origin, GMSH, Python and Dassault Abaqus were employed to assist in the analysis. Three samples were analysed under different conditions: in the first case, the initial sample was examined; for the second case, the sample was subjected to a force of 400 N; for the third case, a force ranging from 100 to 200 N was applied over a period of 50 milliseconds; and for the fourth case, the same force was applied for a period of 5000 milliseconds. The GND analysis of all these cases was carried out using Electron Backscatter Diffraction (EBSD). Additionally, various plots, such as plastic strain, resulting shear stress, von Mises stress, and maximum principal stress, were generated using ABAQUS. Other important data, including Young’s modulus (E), Schmid factor (m), and the product of Young’s modulus and Schmid factor (𝐸.𝑚), were also plotted. These graphs were compared, and a comprehensive study was conducted to understand the likelihood of plastic deformation under different conditions. By conducting the aforementioned analysis and detailed study, a comprehensive understanding of the influence of ultrasound on the density of geometrically necessary dislocations (GNDs) in the nickel-based super-alloy IN617 was achieved.