Solid-State Diffusion Bonding of Commercially pure Titanium and Precipitation Hardening Stainless steel

Solid-state direct diffusion bonding of commercially pure Titanium (Cp-Ti) and precipitation hardening stainless steel (PHSS) has been carried out in the temperature range of 800°C to 1000°C with an interval of 50°C for 3.6 ks under 3.5 Mpa uniaxial load in (4 to 6)×10 Pa vacuum. The effects of temperatures have been investigated with reference to bond strength. The examination revealed that the transition joints achieve tensile strength 108% and shear strength 87.6% higher compared to pure titanium. And the ductility of the joint has been found to be 12.8% when processed at 950°C. The joint structure and intermetallic phases like Fe2Ti, FeTi, Cr2Ti, λ ( solid solution of Fe2Ti and Cr2Ti ), χ ( Fe17Cr7Ti5 ), α-Fe, α-Ti and β-Ti were predicted by optical microscope, SEM-BSE, EPMA and subsequently the presence of intermetallic phases including σ phase (compound of Fe and Cr ) were confirmed by X-ray diffraction (XRD) technique. EPMA also revealed substantial diffusion of Fe, Cr and Ni into the titanium base-metal and titanium traveled a less distance towards PHSS side. Bond strength and hardness of the interface layers were measured by tensile testing and micro-hardness testing respectively. The activation energy Q and growth velocity k of the reacting layers in the diffusion bonded joints were also calculated. The bond strength has been found to be satisfactory at 950°C. Bond strength drops as the volume fraction of intermetallics increased with the rise in bonding temperature (1000°C).