The densification behavior of transition metal diboride compounds was reviewed with emphasis on ZrB2 and HfB2. These compounds are considered ultra-high temperature ceramics because they have melting temperatures above 3000°C. Densification of transition metal diborides is difficult due to their strong covalent bonding, which results in extremely high melting temperatures and low self-diffusion coefficients. In addition, oxide impurities present on the surface of powder particles promotes coarsening, which further inhibits densification. Studies prior to the 1990s predominantly used hot pressing for densification. Those reports revealed densification mechanisms and identified that oxygen impurity contents below about 0.5 wt% were required for effective densification. Subsequent studies have employed advanced sintering methods such as spark plasma sintering and reactive hot pressing to produce materials with nearly full density and higher metallic purity. Further studies are needed to identify fundamental densification mechanisms and further improve the elevated temperature properties of transition metal diborides.


Materials Science and Engineering


Support for this project was provided by the Enabling Materials for Extreme Environments signature area at Missouri University of Science and Technology. Financial support for WGF and GEH was also provided by the Office of Naval Research through contract number N00014-16-1-2303 .

Keywords and Phrases

Densification; Hot pressing; Sintering; Transition metal diborides

International Standard Serial Number (ISSN)

0350-820X; 1820-7413

Document Type

Article - Journal

Document Version

Final Version

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Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.

Publication Date

01 Jan 2020