Diffusion bonding of TI-6AL-4V to AISI 316L stainless steel: mechanical resistance and interface microstructure

The interface microstructure and mechanical strength of joints obtained by diffusion bonding of alloy Ti-6A1-4V to AISI 316L stainless steel are presented. Bonding took place at 850, 900 and 950°C, maintained for different lengths of time (60 to 180 min). The highest recorded shear strength was equal to 382 MPa and was displayed by the specimen bonded at 950°C/180 min. Three different fracture paths were identified, each correlated to a characteristic strength range. From microprobe measurements and x-ray diffraction studies the following interface reaction products were identified: σ phase, α-Ti, Fe2Ti, β-Ti and Fe-Ti. The interface growth kinetics obeyed a quadratic law, indicating diffusion controlled growth of the β-Ti layer. Finally, from correlations identified between β-Ti layer thickness and shear strength variations, some hypotheses on the role of both pores and interface reaction product on mechanical strength were presented.