Interfacial microstructure and mechanical properties of diffusion-bonded titanium-stainless steel joints using a nickel interlayer

Diffusion bonding was carried out between commercially pure titanium and 304 stainless steel using nickel interlayer in the temperature range of 800-950 degrees C for 3.6 ks under 3 MPa load in vacuum. The transition joints thus formed were characterized in optical and scanning electron microscopes. TiNi3, TiNi and Ti2Ni are formed at the nickel-titanium (Ni-Ti) interface; whereas, stainless steel-nickel (SS-Ni) interface is free from intermetallic compounds up to 900 degrees C processing temperatures. At 950 degrees C, Ni-Ti interface exhibits the presence of beta-Ti discrete islands in the matrix of Ti2Ni and the phase mixture of lambda + chi + alpha-Fe, lambda + alpha-Fe, lambda + FeTi + beta-Ti and FeTi + beta-Ti occurs at the stainless steel-nickel interface. Nickel is able to inhibit the diffusion of Ti to stainless steel side up to 900 degrees C temperature; however, becomes unable to restrict the migration of Ti to stainless steel at 950 degrees C. Bond strength was also evaluated and maximum tensile strength of similar to 302 MPa and shear strength of similar to 219 MPa were obtained for the diffusion couple processed at 900 degrees C temperature due to better contact of the mating surfaces and failure takes place at the Ni-Ti interface. At higher joining temperature, the formation of Fe-Ti bases intermetallics reduces the bond strength and failure occurs at the SS-Ni interface. (c) 2006 Elsevier B.V. All rights reserved.