Abstract:The diffusion bonding of V-4Cr-4Ti alloy and pure titanium was achieved by the hot forging process. The interface microstructure and bonding strength of the diffusion joint were analyzed by OM, SEM, EDS, and shear test, respectively. The diffusion joint is about 100 μm wide in total, and can be divided into two zones with different width and microstructure. The SEM analysis across the diffusion interface presents a smooth diffusion interface without any defects. According to the Vickers hardness distribution across the substrates and the diffusion joint, it can be divided into six regions (A, B, C, D, E and F). The boundary zone of region C close to Ti substrate possesses the highest hardness of 332 HV, and the zone of region E close to region D has the lowest hardness(182 HV), while the average hardness of Ti substrate and V-4Cr-4Ti alloy are 190 HV and 258 HV, respectively. The result of shear test shows that the actual shear strength is higher than 165.2 MPa, and the fracture occurred at the boundary zone of titanium substrate close to the diffusion joint, which is mainly ascribed to the stress concentration due to the phase trasition for Ti substrate during cooling process.