High-Strength Diffusion-Bonded Joints of 17-4 Stainless Steel and T64 Alloy Using Nickel and Copper Bilayer

The vacuum-assisted diffusion-bonded joints (DBJs) between 17-4 PH grade stainless steel (SS) and Ti-6Al-4V (T64) using Ni and Cu as transitional bilayer materials were prepared using 3.5 MPa bonding pressure at 750-850 °C for 45 min. Interfaces were characterized using optical and scanning electron microscopes. Atomic interdiffusion across the joining interfaces was assessed using electron probe microanalyzer. For the DBJs processed at 750 °C, layer-wise intermetallic of Cu-Ti type was found at the Cu/T64 interface; however, both the SS/Ni and Ni/Cu interfaces were free from intermetallics. Till 800 °C, Ni and Cu intermediate bilayer materials restricted the movement from T64 to SS, and vice versa. At 825 °C and higher bonding temperatures, both Ni and Cu layers did not impede the atomic movement from T64 to SS; so layer-wise reaction products (σ phase, χ phase, and λ + FeTi) were observed along the SS side. High-strength diffusion-bonded joint was achieved at 775 °C processing temperature, that is, maximum tensile strength of ~ 643 MPa along with ~ 9.3% elongation. The tensile strength of the DBJs gradually decreased with the increase in temperature due to the presence of Ni + Cu + T64 diffusion reaction zone (800 °C) and the evolution and broadening of SS + Ni + Cu + T64 diffusion reaction zone at and above 825 °C.