Spark plasma joining of ZrB₂-SiC composites using zirconium-boron reactive filler layers

Spark plasma joining is used to join ZrB₂-SiC composites with seamless microstructures at the joint that results in retention of high-temperature mechanical and oxidation properties after joining. Our approach uses a spark plasma sintering furnace and Zr-B powder filler layers to join the parts together. The joining processing parameters used to optimize the joint microstructure were filler composition, target temperature, hold time, and volume of filler. A filler of 1 mm³ and spark plasma joining conditions at 1800°C for 300 s resulted in the formation of a joint region that was indistinguishable from the bulk substrates. Room and high-temperature (1350°C) shear strengths of joined substrates measured equal to baseline substrates and oxidation behavior for joined and baseline substrates were equivalent after static air oxidation at 1700°C. X-Ray diffraction measurements show the joint is composed of ZrB₂ and ZrC. We found the joining mechanism to be solid-state bonding of ZrB₂ that formed from the Zr-B filler and reaction bonding by the formation of ZrC. Spark plasma joining rapidly joins ZrB₂-SiC and probably other conductive ultra high-temperature ceramic composites, and has the potential to impact the rapid assembly and joining of complex thermal protection material systems.