Diffusion bonding of commercially pure titanium and 17-4 precipitation hardening stainless steel

Abstract

Commercially pure titanium and 17-4 precipitation hardening stainless steel were diffusion bonded in the temperature range of 850–950 °C for 7.2 ks under 3.5 MPa uniaxial load in vacuum. The transition joints were examined in optical and scanning electron microscope. The chemical compositions of reaction layers in the diffusion zone were determined by energy dispersive spectroscopy and the formation of intermetallics like σ phase, Fe2Ti, FeTi, Cr2Ti, χ, α-Fe, α-Ti and β-Ti phases were predicted. These intermetallics were confirmed by X-ray diffraction technique. The bond strength was evaluated and maximum tensile strength of 102% and shear strength of 81% of those of Ti along with 10.6% ductility were obtained for the diffusion couple, when processed at 900 °C. These occur due to better coalescence of mating surface asperities with respect to 850 °C processing temperature. The volume fraction of the intermetallics increases with the rise in joining temperature and bond strength naturally drops.