Unravelling the Microstructural Properties, Thermomechanical Analysis, Tribocorrosion Behaviour, and Predictive Grain Evolution Modeling of Dissimilar Inconel-Steel Hybrid FSW Joints

Abstract

The present thesis investigates the joining of dissimilar Inconel 718 and SS321 alloys using induction-assisted friction stir welding (IAFSW), with emphasis on process-structure-property relationships. The study systematically examines the influence of welding parameters on material flow, thermal behaviour, dynamic recrystallization, grain-boundary evolution, phase/precipitate characteristics, and mechanical performance. Experimentally validated numerical approaches based on coupled Eulerian-Lagrangian (CEL) modelling and Monte Carlo Potts (MCP) simulation were employed to understand the thermomechanical response and grain evolution during welding. The resulting joints were further evaluated in terms of mechanical properties, tribological behaviour, and electrochemical corrosion performance. The optimum 450/70 condition produced a refined dynamically recrystallized microstructure, favourable grain-boundary characteristics, improved strength and hardness, and enhanced wear and corrosion performance within the investigated process window. In addition, integration of compressed air media cooling (CAMC) with IAFSW was demonstrated to reduce tool loading and wear while enabling stable welding of the high-strength dissimilar alloys. Overall, the work establishes an integrated experimental-computational framework for understanding and improving the performance and industrial feasibility of dissimilar Ni-alloy/steel friction stir joints.