Effect of the pressure welding scheme on the microstructure of solid-state joints from nickel-based superalloys EK61 and EP975 with different phase compositions

Abstract

In recent years, due to the rapid development of the aerospace industry, the need for fundamental studies on high temperature nickel-based superalloys, especially in the field of solid state joints (SSJs), has become even more urgent. This paper presents the results of research on the microstructure of solid state joints of high-alloyed EK61 (Ni3Nb) and EP975 {(Ni3(Al,Ti)} nickel based superalloys with different types of strengthening phase after pressure welding. The pressure welding of the combination of the EK61//EP975 superalloys was carried out in vacuum at a temperature of 925 ºC, which corresponds to the interval of superplasticity manifestation of the EK61 superalloy with an ultrafine-grained microstructure. Two schemes of pressure welding were used in the work: cylindrical specimens when normal compressive stresses act, and model specimens of the "disc–shaft" type when tangential and normal compressive stresses act relative to the joining plane. It is found that both joining schemes lead to the formation of a high-quality solid joint. It is shown that a diffusion transition zone is formed between the joined EK61 and EP975 superalloys during the pressure welding process. The width of the diffusion zone after pressure welding is 8–10 microns. The porosity of the solid state zone does not exceed 15%.