High-temperature phase equilibria in the system Zr-O-N

Powders of Zr, ZrO₂, and ZrN were mixed and pressed to produce samples with different bulk stoichiometries in the ternary Zr-O-N systems. The samples were laser heated above melting, maintained at a high temperature, and quenched. The processed samples were cross-sectioned and studied using scanning electron microscopy, energy dispersive x-ray spectroscopy, and x-ray diffraction. The results pointed to the location of the ternary invariant point Liquid + Gas + ZrO₂ + ZrN on the high-temperature portion of the Zr-ZrO₂-ZrN phase diagram. The ternary liquidus in the Zr-O-N system was further constrained based on the comparison of the results obtained in this work with composition histories of zirconium particles burning in air reported earlier. Elemental analysis of nitrogen-rich inclusions found in the samples showed the existence of an extended compositional range for ternary solid Zr-O-N solutions. X-ray diffraction analysis of the quenched samples indicated that these solutions are likely to be derived from the ZrN phase. A preliminary outline of the subsolidus ternary Zr-ZrO₂-ZrN phase diagram is constructed based on these findings and the interpretations of the well-known binary Zr-O and Zr-N phase diagrams.