Microstructure characterization and tensile shear failure mechanism of the bonding interface of explosively welded titanium-steel composite

The dissimilar joining of TA2/Q235 had attracted great attention because of its important applications in the nuclear fusion, aerospace, petrochemical industry. The possibility of joining TA2 and Q235 irrespective of different thermal expansion coefficients, different melting temperatures, or different mechanical properties was restricted with the conventional welding methods. Explosive welding, as a well-known composite processing technology, could be used to weld two or more similar and dissimilar plates. Which had been used to successfully fabricate TA2/Q235 composite in this work. The failure often occurred near the bonding interface of transition joints and mechanical parts were fabricated by explosive welding in the industrial application and production. Then the tensile-shear test was conducted to investigate the tensile shear failure mechanism at the bonding interface with in-situ SEM, and also nanoindentation was used to identify the mechanical properties. The interface bonding shear strength was around 345 MPa. Further, the microstructure characterization of interfacial zone and the melting and mixing of welding materials were investigated by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The results demonstrated that the failure of the bonding interface occurred along the interface wave direction. It was because that the defects, such as cavities, cracks and brittle intermetallic, in the melted zone of the interface wave. The discontinuities and stress concentration points would result in degraded mechanical properties. The fracture morphology showed microcracks, cleavage plane, dimples, fragmentation of brittle intermetallic compounds, which presented mainly brittle fracture, while ductile fracture existed in some zone. Meanwhile, there were the serious lattice distortion and high internal stress in Ti matrix, while the deformation and elongation of the grain and fine grains formed in Fe matrix.