A Review on Diffusion Bonding between Titanium Alloys and Stainless Steels

High-quality joints between titanium alloys and stainless steels have found applications for nuclear, petrochemical, cryogenic, and aerospace industries due to their relatively low cost, lightweight, high corrosion resistance, and appreciable mechanical properties. This article reviews diffusion bonding between titanium alloys and stainless steels with or without interlayers. For diffusion bonding of a titanium alloy and a stainless steel without an interlayer, the optimized temperature is in the range of 800-950 degrees C for a period of 60-120 min. Sound joint can be obtained, but brittle FeTi and Fe-Cr-Ti phases are formed at the interface. The development process of a joint mainly includes three steps: matching surface closure, growth of brittle intermetallic compounds, and formation of the Kirkendall voids. Growth kinetics of interfacial phases needs further clarification in terms of growth velocity of the reacting layer, moving speed of the phase interface, and the order for a new phase appears. The influence of Cu, Ni (or nickel alloy), and Ag interlayers on the microstructures and mechanical properties of the joints is systematically summarized. The content of FeTi and Fe-Cr-Ti phases at the interface can be declined significantly by the addition of an interlayer. Application of multi-interlayer well prevents the formation of intermetallic phases by forming solid solution at the interface, and parameters can be predicted by using a parabolic diffusion law. The selection of multi-interlayer was done based on two principles: no formation of brittle intermetallic phases and transitional physical properties between titanium alloy and stainless steel.