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

摘要

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.