The effect of intermetallics on the strength properties of diffusion bonds formed between Ti-5.5Al-2.4V and 304 stainless steel

Solid-state diffusion bonding was done to produce transition joints between Ti-5.5Al-2.4V and type 304 austenitic stainless steel in the temperature range of 850-950 deg. C under uniaxial load for 1 h. The diffusion-bonded couples thus produced were evaluated by optical microscopy, scanning electron microscopy, X-ray diffraction and tensile testing. Scanning electron microscopy in back scattered mode reveals the presence of different reaction bands in the diffusion zone. Chemical compositions of these reaction layers were determined by using energy dispersive spectroscopy. The study indicates the existence of σ, Fe2Ti, FeTi and Fe2Ti4O in the reaction zone. These compounds were confirmed by X-ray diffraction technique. It has been observed that with the rise in processing temperature, the width of diffusion zone as also volume fraction of intermetallic phases increases. Highest bond strength (∼272 MPa) has been obtained for the diffusion-bonded assemblies processed at 850 deg. C due to presence of thinner width of brittle intermetallics and the failure occurs in the region somewhere in between FeTi and β-Ti during tensile loading for all the diffusion-welded joints