Mechanical properties of diffusion bonded joints between titanium and stainless steel with nickel interlayer

Abstract

Solid state diffusion bonded joints of commercially pure titanium and 304 stainless steel using a 300 μm nickel interlayer were prepared at 850°C for 1·8–10·2 ks under 3 MPa load in vacuum. The diffusion bonds were characterised by light and scanning electron microscopy. The SEM–BSE images show the existence of different reaction layers in the diffusion zone. The composition of these layers was determined using an electroprobe microanalyser, indicating that TiNi₃, TiNi and Ti₂Ni are formed at the nickel/titanium interface and the stainless steel/nickel interface is free from intermetallics. The presence of intermetallics was confirmed by the X-ray diffraction technique. Nickel can inhibit the diffusion of Ti to the stainless steel side for all bonding times. A maximum tensile strength of ∼312 MPa (∼98% of Ti) and a shear strength of ∼236 MPa (∼81% of Ti) along with ∼9·1% ductility were obtained for diffusion couple processed for 7·2 ks. Observation of fracture surfaces by SEM using EDS demonstrates that failure takes place mainly through the nickel/titanium interface.