Open AccessDensification of ultra-refractory transition metal diboride ceramics
Author(s) -
William G. Fahrenholtz,
Gregory E. Hilmas,
Ruixing Li
Publication year - 2020
Publication title -
science of sintering/science of sintering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.309
H-Index - 25
eISSN - 1820-7413
pISSN - 0350-820X
DOI - 10.2298/sos2001001f
Subject(s) - materials science , spark plasma sintering , ceramic , impurity , sintering , oxide , transition metal , refractory metals , metallurgy , hot pressing , metal , composite material , catalysis , biochemistry , chemistry , organic chemistry
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.