Diffusion bonding of commercially pure titanium to 304 stainless steel using copper interlayer

Abstract

Diffusion bonding was carried out between commercially pure titanium (cpTi) and 304 stainless steel (304ss) using copper as interlayer in the temperature range of 850–950 °C for 1.5 h under 3 MPa load in vacuum. The microstructures of the transition joints were revealed in optical and scanning electron microscopy (SEM). The study exhibits the presence of different reaction layers in the diffusion zone and their chemical compositions were determined by energy dispersive spectroscopy. The occurrence of different intermetallic compounds such as CuTi2, CuTi, Cu3Ti2, Cu4Ti3, FeTi, Fe2Ti, Cr2Ti, T2 (Ti40Cu60−xFex; 5 < x < 17), T3 (Ti43Cu57−xFex; 21 < x < 24) and T5 (Ti45Cu55−xFex; 4 < x < 5) has been predicted from the ternary phase diagrams of Fe–Cu–Ti and Fe–Cr–Ti. These reaction products were confirmed by X-ray diffraction technique. The maximum bond strength of 318 MPa (99.7% of Ti) was obtained for the couple bonded at 900 °C due to better coalescence of mating surface. With the rise in joining temperature to 950 °C, decrease in bond strength occurs due to formation of brittle Fe–Ti bases intermetallics. At a lower joining temperature of 850 °C, bond strength is also lower due to incomplete coalescence of the mating surfaces.