Phase transformations and microstructural features in hafnium nitrides. Issue 15 (December 2017)

• Record Type: Journal Article
• Authors: Schulz, Bradford C.; DiPietro, Steve; Weinberger, Christopher; Thompson, Gregory B.
• Is Part Of: Journal of the European Ceramic Society. Volume 37:Issue 15(2017)
• Page Start: 4532
• Page End: 4538
• Publication Date: 2017-12
• Subjects: Ultra-high temperature ceramics -- Hafnium nitride -- Hot-isostatic pressing -- Diffusion couple -- Microstructure; Ceramic materials -- Periodicals; Composite materials -- Periodicals; Matériaux céramiques -- Périodiques; Composites -- Périodiques; Ceramic materials; Composite materials; Periodicals; Electronic journals; 666.05
• DOI: 10.1016/j.jeurceramsoc.2017.06.016
• Languages: English
• ISSNs: 0955-2219

Abstract

Abstract: Two sets hafnium nitride diffusion couples processed by hot-isostatic pressing at 1200 °C and 1900 °C were formed by reacting Hf with HfN. The 1900 °C couple consisted of Hf grains next to ε-Hf3 N2 grains with fine Hf laths. These were followed by refined ζ-Hf4 N3 grains abutted to the equaxied HfN grains that had a precipitated crisscross pattern of ζ-Hf4 N3 laths on the close-packed planes of HfN; this microstructure agreed with a model's prediction that these interfaces are the most thermodynamically favorable nucleation sites. The 1200 °C couple revealed similar regions except for a lack of this crisscross ζ-Hf4 N3 lath morphology in HfN. The lower temperature is suspected to kinetic limit the condensation of nitrogen vacancies necessary to facilitate lath precipitation. A range of lattice parameters were found to occur for the ε-Hf3 N2 and ζ-Hf4 N3 phases within the couple indicting that these nitrides are not line compounds but accommodate some amount of stoichiometry variation.