The effect of diffusion welding parameters on the microstructural characteristics and mechanical properties of dissimilar joint between 17-4PH steel and Ti6Al4V alloy using nickel interlayer

Diffusion welding is a solid-state welding process in which contacting surfaces to be joined under pressure at elevated temperatures with minimal macroscopic deformation. This study aimed to investigate the effect of diffusion welding parameters on the microstructural characteristics and mechanical properties of the dissimilar joint between 17-4PH steel and Ti6Al4V alloy using Ni interlayer with a thickness of 150 µm. The experiments were performed in a vacuum furnace at three temperatures of 900, 950 and 1050 °C for 45 and 60 min under the pressure of 5 MPa. The results indicate that at the temperatures of 900 and 950 °C, Ni3Ti, NiTi and NiTi2 intermetallic compounds are formed at the nickel-titanium interface, while with increasing the temperature to 1050 °C, NiTi2+Fe2Ti, β-Ti and β-Ti+α-Ti phases are formed at the interface. The minimum microhardness (562 HV) is achieved at the temperatures of 900 °C and time of 45 minutes and the maximum microhardness (700 HV) is obtained at the temperatures of 900 °C and time of 60 minutes. By increasing the time of diffusion welding from 45 to 60 minutes at two constant temperatures of 900 and 950 ° C, the shear strength increases %4.8 and %23.6, respectively. Also, by increasing the temperature of diffusion welding from 900 to 950 °C at fixed times of 45 and 60 minutes, the shear strength decreases %55.3 and %31.7, respectively. The best shear bond strength was 303 MPa, which was obtained at the temperature of 900 ° C and the time of 60 minutes.