Solute Distributions in Tantalum-Containing Zirconium Diboride Ceramics

Solute segregation was examined in zirconium diboride and zirconium-tantalum diboride solid solution ceramics that were produced by reactive hot pressing. Microstructural analysis demonstrated that the ZrB ₂ and (Zr,Ta)B ₂ ceramics reached nearly full relative density and were nominally phase-pure. X-ray diffraction was consistent with full incorporation of Ta into solid solution within the ZrB ₂ structure, and energy-dispersive spectroscopy demonstrated that tantalum was well distributed throughout the bulk of the Ta-doped specimens. The weak characteristic X-rays for B led to inaccurate results for total atom concentrations in boride ceramics by energy-dispersive spectroscopy. Atom probe tomography was used to analyze the amount and spatial distribution of Ta species. No obvious Ta segregation was observed in grains or grain boundaries. However, nitrogen strongly segregated to a grain boundary. This study demonstrated that atom probe tomography is an accurate method for characterizing the amount and spatial distribution of metallic and nonmetallic species in ZrB ₂ ceramics.