Effect of pressure welding temperature on the microstructure and mechanical properties of solid-state joints of wrought nickel-based EK79 and EP975 superalloys

The effect of the pressure welding (PW) temperature on the gradient microstructure formation in the solid-state joint (SSJ) zone of heat-resistant nickel-based EP975 and EK79 superalloys is investigated in this work. The PW was carried out in the temperature range of 1000 –1100°C corresponding to the temperature-rate conditions of superplasticity of EK79 superalloy having fine-grained microstructure. The strength of welded specimens at room temperature was evaluated. It is shown that in the temperature range of 1000 –1100°C quality solid-state joints were obtained from dissimilar EK79//EP975 superalloys. It is found that the more heat resistant EP975 superalloy is thermally stable at temperatures of 1000°C and 1050°C and at the welding temperature of 1100°C a coarsening of the matrix phase is observed. Growing γ-phase grains to a size not exceeding of 10 μm in the EK79 superalloy was observed at 1050°C and 1100°C. It was found that a transition diffusion zone in the SSJ zone is formed, the width of which increases with increasing temperature from 10 to 20 μm. The maximum strength (σUTS =1450 MPa) of the SSJ of EK79//EP975 was achieved after PW at 1050°C.