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

Abstract

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.