Effect of Element Ni Diffusion on Microstructure and Mechanical Properties of Brazed Joints of Cemented Carbide and Steel

YG15 cemented carbides and 35CrMo steel were brazed by Ag-based filler metal with different contents of element Ni. The effect of the Ni content, brazing temperature and ultrasonic vibration on the microstructure and mechanical properties of the joints was investigated. Results show that continuous α-Cu solution layers can be obtained by increasing the Ni content, and the shear strength peak is 295 MPa with the 4.7 wt% Ni filler metal at the brazing temperature of 800℃. The brazing temperature influences the depleted zone width of element Co of joints through the impact on the diffusion of element Ni. The minimum of the depleted zone width of element Co is observed in the joints at the brazing temperature of 730℃, and the shear strength of the joint reaches maximum 350 MPa. The brazing process with ultrasonic vibration can enlarge the width of the depleted zone of element Co of the joints, decrease the content of eutectic structure, and drive the migration of WC particles into bonds. The maximum shear strength 371 MPa of the joints with 17.5 μm wide depleted zone of element Co is obtained with ultrasonic brazing for 30 s, which is increased by 6% compared with that without ultrasound. © 2017, Science Press. All right reserved.