Influence of interface microstructure on the mechanical properties of titanium/17-4 PH stainless steel solid state diffusion bonded joints

In the present study, titanium was diffusion bonded to a type 17-4 precipitation hardening stainless steel in vacuum at different temperatures and times. Bonded samples were characterized using light microscopy, scanning electron microscopy (SEM) and X-ray diffraction technique (XRD). The inter-diffusion of the chemical species across the diffusion interface was evaluated by electron probe microanalysis (EPMA). Up to 850 degrees C for 60 min, FeTi phase was formed at the diffusion interface; however, alpha-Fe + lambda, chi, Fe2Ti and FeTi phases and their phase mixtures were formed above 850 degrees C for 60 min and at 900 degrees C for all bonding times. The maximum tensile strength of similar to 342.4 MPa and shear strength of similar to 260.3 MPa along with 12.8% elongation were obtained for the diffusion couple processed at 950 degrees C. The thicknesses of different reaction products at the bond interface play an important role in determining the mechanical properties of the joints. The residual stress of the bonded joints increases with the increases in bonding temperatures and times. (C) 2011 Published by Elsevier Ltd.