Discussion On Mechanism For Vacuum Hot Rolling Bonding Of Titanium Alloy And Stainless Steel

The vacuum hot rolling bonding of Titanium alloy (Ti6Al4V) and stainless steel (0Cr18Ni10Ti) using no interlayer and the interlayer of Cu was investigated. The tensile strength was tested and the microstructure of the joints and the fractograph were analyzed by optical, scanning electron microscopy, XRD and energy spectrum analysis. The bonding mechanism of the vacuum hot roll bonding was discussed.The results showed that the TC4 plate would be haunch-up when there no interlayer and the situation worsening with the increase of the compression ratio. The reaction layers and the micro-crack were occurred in joints which induced the failure of joining. The results using Cu interlayer shows that the haunch-up of the TC4 plate and the formation of the Ti-Fe intermetallic compounds were prevented. The tensile strength was depended on the thickness of the compound layer between the Cu-TC4 interface and the max strength is about 340MPa when the bonding temperature is 780℃and the compression ratio is 20%.The thickness of the compound layers would increase with the rise of the bonding temperature. It would lead to decrease the tensile strength. The bond can not form if the bonding temperature is too low. The compression ratio decides the distortion of the plates which make the surfaces connect close. The strength would increase with the compression ratio at beginning and be stable when the ratio is large enough.The process of the vacuum hot roll bonding was composed of three stages: the flow of the metals and the friction of the interface before rolling, the distortion of the plates and the activation of the atoms of the two surfaces when being rolling and the diffusion of the interface after rolling.