Microstructure evolutions and interfacial bonding behavior of Ni-based superalloys during solid state plastic deformation bonding

Abstract

As an advanced solid state bonding process, plastic deformation bonding (PDB) is a highly reliable metallurgical joining method that produces significant plastic deformation at the bonding interface of welded joints through thermo-mechanical coupling. In this study, PDB behavior of IN718 superalloy was systematically investigated by performing a series of isothermal compression tests at various processing conditions. It was revealed that new grains evolved in the bonding area through discontinuous dynamic recrystallization (DDRX) at 1000–1150 °C. Electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) results revealed that the bonding of joints is related with interfacial grain boundary (IGB) bulging process, which is considered as a nucleation process of DRXed grain under different deformation environments. During recrystallization process, the bonded interface moved due to strain-induced boundary migration (SIBM) process. Stored energy difference (caused by accumulation of dislocations at the bonding interface) was the dominant factor for SIBM during DRX. The mechanical properties of the bonded joints were dependent upon the recrystallized microstructure and SIBM ensued during PDB.