Microstructural evolution, metallurgical reactions, and the mechanical properties of pure titanium and carbon steel sheets bonded via hot-roll diffusion with a nickel interlayer

This study investigated the microstructural evolution and mechanical properties of titanium-carbon steel bi-metallic composite sheets fabricated via hot-rolling diffusion with a nickel interlayer at temperatures of 800, 850, or 900°C. Scanning electron microscopy and energy-dispersive X-ray spectroscopy revealed layers of NiTi2, NiTi, and Ni3Ti phases at the Ti-Ni interface. We also observed interfacial σ + β Ti and β-Ti phases. Note that the carbon steel-Ni interface revealed no reaction layers or intermetallic compounds under any of the processing temperatures. The highest shear strength (∼470 MPa) was obtained at a processing temperature of 850°C. The highest peel strength (∼21 N/mm) was obtained at a processing temperature of 900°C. Lower bonding temperatures were shown to reduce bond strength by hindering atomic diffusion, whereas higher bonding temperatures led to the formation of excessive intermetallic compounds. Both conditions resulted in joint failure at the Ti-Ni interface and extensive cleavage planes with various alignments on fracture surfaces. Overall, a hot-rolling temperature of 850°C provided the optimal tradeoff between interfacial bonding strength and ductility.