Abstract: A Ni-B₄C macroscopic diffusion welding couple and a Ni-15wt%B₄C composite fabricated by spark plasma sintering (SPS) were used to understand the micro-scale diffusion bonding between metals and ceramics. In the Ni-B₄C macroscopic diffusion welding couple a perfect diffusion welding joint was achieved. In the Ni-15wt%B₄C sample, microstructure analyses demonstrated that loose structures occurred around the B₄C particles. Energy dispersive X-ray spectroscopy analyses revealed that during the SPS process, the process of diffusion bonding between Ni and B₄C particles can be divided into three stages. By employing a nano-indentation test, the room-temperature fracture toughness of the Ni matrix was found to be higher than that of the interface. The micro-diffusion bonding between Ni and B₄C particles is quite different from the Ni-B₄C reaction couple.