Phase Transformations in the Surface Layer of Compact Zirconium Nitride-Based Ceramics

Abstract

We have studied structural, morphological, and phase transformations in the surface layer of compact zirconium nitride-based ceramics during high-temperature annealing in vacuum, nitrogen, and air. The formation of oxygen-containing phases during heat treatment of ZrN is controlled by bulk and grain-boundary oxygen diffusion. At the beginning of the process, oxygen is supplied by an amorphous surface layer, which always forms during the ceramic preparation process. In air, the process is driven by oxygen indiffusion from the gas phase across an initially forming porous oxide layer. Grain-boundary oxygen diffusion leads to the formation of a crystalline zirconium oxide layer on grain boundaries and crack nucleation.