Numerical Analysis Of Evolution Of Dynamic Recrystallization In Inertia Friction Welding Process Of Ni-based Superalloy

The inertia friction welding is widely used in aero-engine,which is one of excellent manufacturing technologies of rotating structure parts in aero-engine.The thermal-mechanical coupling process and the evolution of dynamic recrystallization have great influences on microstructures and mechanical properties of the joints.Therefore,it's essential to study the temperature field,stress and plastic strain field and the evolution of dynamic recrystallization,which is the basis of controlling the welding quality and the microstructure and properties of the joints.The results of welding experiment indicate that the dynamic recrystallization occurs in friction interface.The hardness of friction interface center is higher than that of marginal zone.All the welded joints at different parameters(initial speed,friction pressure)are fracture in base metal in tensile tests.The dynamic recrystallization behavior has an important effect on mechanical properties.In order to simplify the calculation process,based on the rigid/plastic body model of friction pair,the instantaneous numerical model of inertia friction welding was established by finite elements simulation software,which was verified by flash temperature,the shape of flash and the geometrical dimensions of flash,and the maximal error is less than 12.76%.So,the founded model can be used to analyze the thermal-mechanical coupling process and evolution process of microstructures in inertia friction welding process.The simulation results of the thermal-mechanical coupling process indicate that the distribution of heat flux and the temperature distribution along the radial direction are characterized with the "dual hump" distribution,in which the maximal heat flux and the highest temperature appear at the position of 2/3 radius,which is determined by the distributions of linear velocity and friction pressure on the friction interface.The annular high-temperature zone appears and has an important effect on stress and strain.Thus,the distributions of stress and strain along the redial direction are also characterized the "dual hump" distribution.The axial compressive stress in the friction interface center are higher than that at marginal zone.And the axial compressive stress will transform to tensile stress gradually.The plastic strain of friction interface is maximum and it increases with increasing friction time.The plastic strain at the friction center is higher than that at marginal zone.Based on the results of thermal-mechanical coupling process,the model of microstructure evolution was established by developing user subroutines.The simulation results have a better approach to the experiment results.The dynamic recrystallization is initiated at the annular zone(0.286R-0.552R)and it will extend to the friction interface.The grain size at the annular zone is smaller than that at peripheral region.With the increase of friction time,the grain size of the annular region is larger than that of other regions because of the annular high-temperature region.The dynamic recrystallization of the microstructures in the friction interface will take place earlier when the friction pressure and initial speed is higher.The higher friction pressure,the smaller grain size.In the late stage of inertia friction welding,the grain size of friction welded joint under low rotary inertia is smaller than that under high rotary inertia.