Microstructure and mechanical properties of diffusion bonded joint between tungsten and ferrtic steel using vanadium/nickel composite interlayer

The diffusion welding characteristic between W and ferrite steel(FS) interface was investigated in vacuum hot pressing furnace at 1 050℃ for 1h with 10 MPa, using 3 mm V foil and 1 mm Ni foil as interlayer. The microstructure, element compositions, phase compositions and microhardness of joints were observed and measured with field-emission scanning electron microscopy(FE-SEM), energy dispersive spectroscopy(EDS), electron probe micro-analyzer(EPMA), x-ray diffractometer(XRD) and nanoindenter, respectively. The tensile strength was tested by mechanical testing machine. The results showed that, a reliable bonding between W and FS could be gained by using vanadium/nickel composite interlayer. The W/FS joint consisted of a multilayer sandwich structure, including the transition zone of W/V, the residual V interlayer, the diffusion layer of V/Ni, the residual Ni interlayer and the diffusion layer of Ni/FS. Meanwhile, the transition zone of W/V and Ni/FS were mainly composed of solid solution structure and the V/Ni diffusion layer with the highest microhardness of 9.7GPa. The joint had a multilayered structure consisting of VC layer/mixing layer of VC and Ni-V intermetallics/Ni-V intermetallics layerand the tensile strength of joint reached 164 MPa and the samples fractured through the V/Ni interface because of the presence of brittle VC phase and Ni-V intermetallics.