Direct solid-state diffusion bonding of zirconium carbide using a spark plasma sintering system

The authors conducted direct solid-state diffusion bonding of zirconium carbide (ZrC)-sintered materials with different average grain sizes of 3.5, 75 and 35 gm using a spark plasma sintering system. ZrC samples were bonded at 1300-2000 degrees C for 20 min with no defects or oxidation. Shear tests on the ZrC-ZrC joints at room temperature revealed that the bonding temperature to obtain joints with a strength at the bonding interface that is higher than the fracture strength of the base materials could be reduced by reducing the ZrC average grain size. Microstructure studies around the bonding interface showed that the bonding process was controlled by grain-boundary diffusion, and the dominant driving force was a lowering boundary energy at the intersection of the grain boundary and the bonding interface (i.e., triple junctions at the bonding interface). Grain boundary migration across the bonding interface at the triple junctions was suggested to increase joint strength. The higher density of the triple junctions derived from the reduced ZrC grain size is thought to enhance grain boundary migration and increase the driving force and diffusion paths for grain boundary diffusion, which results in the formation of joints with a higher bonding interface strength. (C) 2016 Elsevier Ltd. All rights reserved.