Preliminary Study on Diffusion Bonding of V-4Cr-4Ti/Ti by Hot Forging Process

The diffusion bonding of V-4Cr-4Ti alloy and commercially pure titanium was performed by a hot forging process. The interface microstructure and bonding strength of the diffusion joint were analyzed by OM, SEM, EDS, and shear test. According to OM and SEM analysis, the diffusion joint is about 100 lam wide in total. It presents a smooth diffusion interface without any defects, and can be divided into two zones with different widths and microstructures: zone I is the needlelike Widmanstatten alpha-beta structure consisting of beta-Ti and alpha-Ti, while zone II is a solid solution of V and Cr in Ti, which is caused by the interdiffusion of the strong beta-stabilizers V and Cr in the V-4Cr-4Ti alloy into the Ti matrix. According to the Vickers hardness distribution of the substrates and the diffusion joint, it can be divided into six regions (A, B, C, D, E and F). The region C near the boundary of Ti substrate has the highest hardness of 3320 MPa, and the region E close to the region D has the lowest hardness (1820 MPa), while the average hardness of the Ti substrate and V-4Cr-4Ti alloy is 1900 MPa and 2580 MPa, respectively. The shear test result shows that the actual shear strength of diffusion joints is higher than 165.2 MPa, and the fracture occurs at the transitional interface between the titanium substrate and the diffusion joint, which is mainly ascribed to the stress concentration caused by the phase transition of the Ti substrate in the cooling process.