Effect of Bonding Temperature on Microstructure and Properties of TransientLiquid Phase Diffusion Bonded Joint of Titanium/Steel Composite Pipe

Taking composite steel pipe with TA2 industrial pure titanium lining and 20 steel coating as the research object, and BNi₂ amorphous alloy foil as the interlayer, the titanium/steel composite pipe was welded by transient liquid phase diffusion bonding at bonding temperatures of 1 130-1 200℃ under argon protection. The effect of bonding temperature on the microstructure and properties of titanium/steel composite pipe joints was investigated. The results show that the joints at different bonding temperatures were formed well without macroscopic defects such as holes and cracks. With increasing bonding temperature, the equiaxed microstructure of weld at the titanium side grew up, α→α'+β phase transition occurred, and the weld boundary became blurred gradually. The acicular ferrite and pearlite in the weld at the steel side became thicker, the black brittle phase gradually disappeared, and the diffusion distance of elements of interlayer and base material increased. The joints welded at different bonding temperatures all fractured in the weld at the titanium side. With increasing bonding temperature, the tensile strength of the joint increased first and then decreased. When the bonding temperature was 1 180℃, the tensile strength was the biggest of 460 MP, and the fracture form was ductile-brittle mixed fracture.