Joining of ultra-refractory carbides

Transient-liquid-phase (TLP) bonding enables joining at reduced temperatures relative to those required by more traditional joining routes while preserving the potential for high-temperature applications of ultrarefractory carbides. Pure ZrC, HfC and TaC ultra-high temperature ceramics (UHTCs) were joined using a multilayer Ni/Nb/Ni interlayer by executing a 30-min bonding cycle under low load (<1.3 kPA) at 1400 °C in a high-vacuum furnace. Microstructural and microchemical analyses of the resulting joints were conducted using scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The SEM/EDS analysis suggests that the (Ni,Nb)-containing liquid formed during bonding wets the carbide matrices properly, resulting in well-bonded crack-free interfaces between the UHTCs and the Nb-rich interlayer. Although there were many similarities between the resulting joints, the microstructures in the interlayer-carbide transition regions also exhibited considerable diversity.