Nano surface generation by single point diamond turning for low-pressure diffusion bonding of copper

This study has demonstrated a combination of single-point diamond turning (SPDT) and solid-state diffusion bonding (SSDB) to achieve low-pressure joining of Cu plates. SPDT on the faying surfaces has resulted in nano-level surface roughness of Sa 1.56 nm and Ra 1.32 nm. Diffusion bonding experiments were performed by varying bonding temperatures from 600 °C to 800 °C and at a low bonding pressure of 4 MPa. It was interesting to note that a low-temperature bonding at 600 °C has resulted in a bonding ratio of 92.2 %, and it significantly enhanced to 98.4 % at 800 °C. Complete grain boundary migration was observed along the joint interface for the sample bonded at 800 °C. The shear load for joint failure increased from 13.06 kN to 18.36 kN with an increase in bonding temperature, which was correlated with the microstructural observation. The fractography study indicated a ductile mode of failure. Low-pressure diffusion bonding of the Cu plate with integrated channels was successfully demonstrated without deforming the channels. Precision alignment of the arrayed channels for conformal cooling applications could be achieved using a combination of SPDT and SSDB, which would be challenging with other joining techniques.