Effect of Nb interlayer thickness on interfacial products and mechanical properties of Ti–6Al–4V/EH690 steel clad plate by vacuum hot rolling

The high content of alloying elements in Ti alloys and high-strength steels, combined with the requirement for quenching and tempering heat treatment during the fabrication process of the clad plate, leads to complex interfacial products and poor bonding properties. An Nb interlayer was introduced to enhance the mechanical properties of Ti alloy/steel clad plates. This work investigated the effect of Nb interlayers with initial thicknesses of 10, 25, and 50 μm on the evolution of interfacial products and bonding properties. The results indicated that when the interlayer was thin (10 μm thick), the diffusion of Ti, Fe, and C in the matrix and clad materials could not be completely inhibited due to the uneven distribution of the Nb interlayer at the interface. TiC, NbC, Nb2C, and Fe2Nb were detected at the Nb/steel interface. With the thickness of the interlayer increased (reaching 25 μm or 50 μm), the influence of uneven deformation on the interlayer was weakened, and the Nb/steel interface was composed of Nb2C and Fe2Nb. The tensile shear test indicated that the fracture occurred at the Nb/steel interface and the Nb interlayer. The plasticity of the micrometer Nb interlayer decreased with the increase in interlayer thickness. Therefore, more cracks and brittle fracture characteristics were observed in the fracture surface of the 50 μm thick Nb interlayer sample. The clad interface with a 25 μm thick Nb interlayer exhibited the highest interfacial shear strength of 295 MPa due to the few intermetallic compounds (IMCs) at the Nb/Steel interface and the excellent plasticity of the Nb interlayer.