Evolution of Interfacial Microstructure of Ni-Co Base Superalloy During Plastic Deformation Bonding and Its Bonding Mechanism

Superalloys with excellent high-temperature resistance and oxidation resistance have been widely used in aviation and energy fields. The new Ni-Co base superalloy is considered a candidate for the next generation of turbine discs due to its higher performance of mechanical properties and microstructure stability at high temperatures. However, tungsten inert gas (TIG) welding, metal inert gas (MIG) welding, and other welding techniques are not suitable for welding the new Ni-Co base superalloy because the Al + Ti content of the alloy reaches 7.5%, while traditional welding techniques (electron beam welding, friction welding, and diffusion welding) also have some disadvantages. For example, friction welding has certain requirements on the shape of the sample, and it is not suitable for welding largevolume alloys. Diffusion welding requires a long heat retention period and a harmful precipitation phase exists at the interface. A new welding method is applied in this study to solve the problem of welding nickel-based superalloy, achieving a better bonding effect. The Gleeble 3500 thermal simulator was used to study the plastic deformation bonding of Ni-Co base superalloys in a temperature range of 1000-1200 degrees C and a strain range of 5%-40% with a strain rate of 0.001 s(-1). The recrystallization behavior of the interface was studied by OM, EBSD, and TEM, and the bonding mechanism of the interface was clarified. The results showed that the resistance to deformation of the alloy was low when the plastic deformation bonding was performed at 1150 degrees C, and there was no risk of cracking of the alloy. Plastic deformation bonding experiments with different deformations had shown that the alloy can achieve complete bonding of the interface under the condition of 40% deformation, and its mechanical properties can reach the same level as the matrix. The tensile fracture analysis showed that the fracture profile of the 40% deformed joint was consistent with the base material, showing a ductile fracture pattern. The results of EBSD and TEM showed that the coarse grains near the interface were first refined during the plastic deformation. With the increase of deformation, the refined grain removed the original interface by the migration of the interfacial grain boundaries with the assistance of a continuous dynamics recrystallization process and ultimately led to the bonding of the interface.