Vacuum hot roll bonding of titaium to stainless steel using Cu and Nb composite interlayer

This article describes a study of the application of a vacuum hot roll bonding technique to Ti alloy plate and stainless steel plate using the composite interlayer of copper(pure copper and copper contains lanthanon Yt)and Nb sheet.The tensile strength was tested and the microstructure of the joint interface, fractograph and the structure of copper interlayer were analyzed by optical and scanning electron microscopy, XRD, energy spectrum analysis. The results showed that the defects such as separation and crack were not observed at interface, and there are no intermetallic compounds formed after bonding. There existed a transition layer at Nb-Ti interface, the thickness of which is about 2.5μm and the thickness of transition layer at Cu-SS and Nb-Cu interface is about 1.9μm. At copper grain boundary the voids were observed and the fractograph showed crack along the grain boundary.Doping of the lanthanon Yt can reduce the grain size. No voids appear in copper layer with Yt comparing with without Yt with the same bonding parameters, and the effect of reducing grain size is more efficient with the content of Yt in copper increasing from 0.01% to 0.02wt%. Comparing with the specimen using pure copper interlayer, the tensile strength increased 51.3 MPa(Yt 0.01wt% in Cu) and 61.7 MPa(Yt 0.02wt%in Cu), respectively.