Omnidirectional simulation analysis of thermo-mechanical coupling mechanism in inertia friction welding of Ni-based superalloy

The coupling between heat and pressure is the kernel of inertia friction welding (IFW) and is still not fully understood. A novel 3D fully coupled finite element model based on a plastic friction pair was developed to simulate the IFW process of a Ni-based superalloy and reveal the omnidirectional thermo-mechanical coupling mechanism of the friction interface. The numerical model successfully simulated the deceleration, deformation processes, and peak torsional moments in IFW and captured the evolution of temperature, contact pressure, and stress. The simulated results were validated through measured thermal history, optical macrography, and axial shortening. The results indicated that interfacial friction heat was the primary heat source, and plastic deformation energy only accounted for 4% of the total. The increase in initial rotational speed and friction pressure elevated the peak temperature, reaching a maximum of 1525.5 K at an initial rotational speed of 2000 r/min and friction pressure of 400 MPa. The interface heat generation could form an axial temperature gradient exceeding 320 K/mm. The radial inhomogeneities of heat generation and temperature were manifested in a concentric ring distribution with maximum heat flux and temperature ranging from 2/5 to 2/3 radius. The radial inhomogeneities were caused by increasing linear velocity along the radius and an opposite distribution of contact pressure, which could reach 1.7 times the set pressure at the center. The circumferential inhomogeneity of thermo-mechanical distribution during rotary friction welding was revealed for the first time, benefiting from the 3D model. The deflection and transformation of distribution in contact pressure and Mises stress were indicators of plastic deformation and transition of quasi-steady state welding. The critical Mises stress was 0.5 times the friction pressure in this study. The presented modeling provides a reliable insight into the thermo-mechanical coupling mechanism of IFW and lays a solid foundation for predicting the microstructures and mechanical properties of inertia friction welded joints.