Joining and integration of ZrB2-based ultra-high temperature ceramic composites using advanced brazing technology

Zirconium diboride-SiC (ZS) particulate ceramic-matrix composites containing either carbon powder (termed ZSC composite) or SCS-9a silicon carbide fibers (termed ZSS composite) were joined to titanium and Inconel 625 using Pd-base brazes, Palco and Palni (T (L) similar to 1492-1513 K). The joints exhibited intimate contact and evidence of interdiffusion of Zr, Si, Pd, and Co, with the Palni joints exhibiting most extensive chemical interaction, greater propensity toward cracking, and partial melting of the Inconel substrate. The joint region comprised of braze-plus-interaction zone exhibited comparable Knoop hardness in Palni and Palco joints. The fully dense ZS had the highest (2000-2600 HK200) and ZSC the lowest (300-750 HK200) Knoop hardness. The ZSS composites displayed a large dispersion in hardness because of incomplete densification (similar to 30% porosity) and transversal cracking from the CTE mismatch between SCS-9a fibers and the ZS matrix. Steady-state thermal calculations reveal that for joined assemblies (similar to 0.51 cm total thickness in the study), joining Ti or Inconel to ZS shall decrease the thermal resistance by nearly 33-43% relative to the metal substrate, thus enhancing the heat dissipation capability in advanced components made using such joints.