Reactive diffusion bonding between commercially pure titanium and 304 stainless steel using nickel interlayer

Diffusion bonding was carried out between commercially pure titanium and 304 stainless steel using nickel as interlayer in the temperature range of 800-900degreesC for 5.4 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 Ni-Ti interface whereas, 304 ss-Ni diffusion zone is free from intermetallic compounds at 800 and 850degreesC processing temperatures. At 900degreesC, Ni-Ti interface exhibits the presence of alpha-beta Ti discrete islands in the matrix of Ti2Ni and the phase mixture of alpha-Fe+lambda+chi occurs at the ss-Ni interface. Nickel is able to inhibit the diffusion of Ti to 304 ss side up to 850degreesC; however, becomes unable to restrict the migration of Ti to stainless steel at 900degreesC. Highest bond strength of 80 % of that of titanium has been obtained for the diffusion couple processed at 850degreesC owing to the better coalescence of the mating surfaces and failure takes place from Ni-Ti interface. At higher joining temperature, the formation of Fe-Ti intermetallics reduces the bond strength and failure in tensile loading occurs from ss-Ni interface.