Diffusion bonded transition joints of titanium to stainless steel with improved properties

Abstract

Diffusion bonding was carried out to produce transition joints between commercially pure titanium (cp Ti) and 304 stainless steel (304 ss) in the temperature range of 800–950 °C, under uniaxial pressure of 3 MPa for 5.4 Ks. The transition joints were evaluated by tensile testing, light microscopy, electron probe micro-analysis and X-ray diffraction. The study indicates that transition joints achieve 76% strength of pure Ti along with ∼5% ductility when processed at 850 °C. Electron probe microanalysis reveals substantial diffusion of Fe, Cr and Ni in the Ti side and Ti travels less distance in stainless steel matrix. A number of intermetallics σ phase, FeTi, Fe 2Ti 4O, NiTi and NiTi 2 have been identified by X-ray diffraction near the interface. Increases in the joining temperature cause the volume fraction of intermetallics to increase. These intermetallics lower the strength of diffusion bonds when processed at higher temperature.