| When titanium alloy directly bonded to stainless steel, various intermetallics formed at bonding interface by inter-diffusion between titanium and stainless steel, which makes embrittlement of the bonding joints. In addition, high internal stress results due to the large difference of linear expansion coefficient between these materials. The paper aims at bonding of titanium alloy and stainless steel by vacuum hot roll bonding. The microstructures of the bonding interfaces were analyzed by optical and scanning electron microscopy, X-Ray Diffraction, energy spectrum analysis and nano-indentation. The bonding mechanism of the vacuum hot roll bonding was investigated.When titanium alloy and stainless steel were directly bonded at bonding temperature 800℃, there were unbonded zones across the interface. At bonding temperature 900℃, intermetallic especially Cr rich zone formed across titanium alloy/stainless steel interface make embrittlement of the bonding joints. When bonding temperature equals to or lower than 750℃, titanium alloy and stainless steel cannot bonded directly, and when temperature equals to or higher than 950℃, they cannot bonded, too. The bonded joints achieve the maximum tensile strength of 77.3MPa when processed at bonding temperature of 850℃and reduction of 20%.Vacuum hot roll bonding was carried out between titanium alloy and stainless steel using copper interlayer. Copper interlayer can block the diffusion Fe, Cr and Ni to Ti side and Ti to stainless steel side, and Fe-Ti intermetallics are not formed at the interface. There are no transition layers at SS/Cu interface. The bonding type of Cu-SS is solid solution, and the structure of interface is ruleless inlaid. Brittle Cu-Ti intermetallics are formed at the copper /titanium alloy interface. With the rise in joining temperature, decrease in tensile strength occurs due to incensement of the volume fraction of intermetallics. The tensile specimens fractured at intermetallic layers or between intermetallic layer and Cu interlayer. The thickness of intermetallics at copper/titanium alloy interface depends mainly on bonding temperature, less on reduction. The bonded joints achieve the maximum tensile strength of 343MPa when processed at bonding temperature of 780℃and reduction of 20%.Vacuum hot roll bonding was carried out between titanium alloy and stainless steel using nickel interlayer. Nickel interlayer can completely block the diffusion Fe, Cr and Ni to Ti side and Ti to stainless steel side, and Fe-Ti intermetallics are not formed at interface. There are no transition layers at SS/Ni interface. The bonding type of SS-Ni is solid solution, and the structure of interface is ruleless inlaid. Brittle Ni-Ti intermetallics are formed at the nickel/titanium alloy interface. With the rise in bonding temperature, decrease in tensile strength occurs due to increasing of the volume fraction of Ni-Ti intermetallics. The tensile specimens fractured at brittle intermetallic layers or between intermetallic layer and Ni interlayer. The thickness of intermetallic at nickel/titanium alloy interface depends mainly on bonding temperature, less on reduction. The bonded joints achieve the maximum tensile strength of 440.1MPa when processed at bonding temperature of 760℃and reduction of 20%.Vacuum hot roll bonding was carried out between titanium alloy and stainless steel using Nb interlayer. Nb interlayer can completely block the diffusion Fe, Cr and Ni to Ti side and Ti to stainless steel side, and Fe-Ti intermetallics are not formed at the interface. With the rise in bonding temperature, decrease in tensile strength occurs due to increasing of the volume fraction of Fe-Nb intermetallics. And with the increasing of bonding temperature, the thickness of solid solution layer increases. The thickness of intermetallic at Fe-Nb interface depends mainly on bonding temperature, less on reduction. The bonded joints achieve the maximum tensile strength of 430MPa when processed at bonding temperature of 800℃and reduction of 20%.The behavior of plastic deformation of dissimilar materials experienced during the rolling process was calculated by finite element software MSC.Marc. The calculation results show that the metal plastically deforms and extends, but the oxide is brittle and can respond to stress only by fracturing. During rolling process, the oxide film will therefore be fractured and fragmented, and this allows metal-metal contact and bond. Using soft material as interlayer the extent of mutual slipping across interfaces becomes bigger.The physical process of roll bonding has been investigated. The results showed that bonding of materials is not depend on atomic diffusion but realizes during the process of rolling. The process of the vacuum hot roll bonding was composed of five steps: the bonding surface contact, the fracture of the surface oxide layer and impurity, the extrusion of fresh metal through cracks in rolling and bonding of metals, the inter-diffusion at interface after rolling and the bonding of whole surface.The bonding between titanium alloy and stainless steel transition joint and titanium alloy or stainless steel by TIG welding was carried out. Titanium alloy/stainless steel transition joint bonded directly cracked at their interface while it experiences TIG welding. Transition joint using Cu interlayer after TIG welding, micro-cracks formed on these regions of Cu/TC4 interface between different intermetallic layers and between intermetallic layer and Cu, so the maximum tensile strength of them achieve only 40.77MPa; Transition joint using Ni or Nb interlayer after TIG welding, the microstructure of interfaces does not change significantly, and the maximum tensile strength of them achieve 431MPa and 421.6MPa, respectively.
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