Variation in the reaction zone and its effects on the strength of diffusion bonded titanium–stainless steel couple

Abstract

Solid state bonding was carried out between commercially pure titanium and 304 stainless steel at 850 °C temperature for 30–150 min under uniaxial load in vacuum. The transition joints were characterized using optical and scanning electron microscopes and revealed the presence of reaction layers in the diffusion zone. The chemical composition of these reaction products was determined by energy dispersive spectroscopy and the presence of phase/phase mixtures σ, α-Fe + χ, χ + λ, λ + FeTi + β-Ti and β-Ti were predicted. Their existence was also confirmed by X-ray diffraction technique. The concentration–penetration plots for Ti, Fe, Cr and Ni are obtained from electron probe microanalysis, which also exhibit concentration gaps in the profile indicating formation of intermetallics in the diffusion zone. The width of intermetallic phases attains its maximum for 90 min joining time, then drops and again rises for 150 min bonding time. The maximum bond strength of 76% of that of titanium was achieved for the assemblies processed for 90 min owing to better coalescence of the mating surfaces, though the volume fraction of intermetallics is high.