Application of Box–Behnken design for fabrication of titanium alloy and 304 stainless steel joints with silver interlayer by diffusion bonding

• Diffusion bonding of Ti–6Al–4V to SS304 with silver interlayer was successful.
• Hardness and shear strength increased with the increase in the bonding temperature.
• Shear strength of 149 MPa and 18% strain to failure were achieved.
• Joint efficiency of 80% was obtained for the Ti–6Al–4V and SS304L joints.

Direct bonding between titanium (Ti)/titanium alloy(Ti alloy) and stainless steel (SS) promotes the formation of various Fe–Ti and Fe–Cr–Ti intermetallics in the diffusion zone, because the solid solubility of Fe, Cr, Ni and Ti in each other is limited and these intermetallics weaken the mechanical properties of the joint. The present study focuses on the titanium alloy Ti–6Al–4V diffusion bonded to AISI 304 stainless steel with silver foil as an interlayer. The process parameters were chosen appropriately and hence, the bonding is achieved without any defect. Box–Behnken design is used to decide the optimum number of experiments required to do the investigation. Microhardness measurements and the lap shear test were carried out to determine the hardness and strength of the joints respectively. The results show that atomic diffusion and migration between Ti and Fe or C are effectively prevented by adding pure Ag as the interlayer metal. The results from mechanical testing showed that shear strength values have a direct relationship with bonding time. The maximum lap shear strength of 149 MPa and 18% strain to failure was observed for joints obtained with bonding time of 60 min. However, effective bonding was not possible at 850 °C due to incomplete coalescence of mating surfaces.

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