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Densification Behavior and Microstructure Evolution of Hot‐Pressed HfB 2
Author(s) -
BrownShaklee Harlan J.,
Fahrenholtz William G.,
Hilmas Greg E.
Publication year - 2011
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1551-2916.2010.04063.x
Subject(s) - microstructure , materials science , carbon fibers , boron carbide , boron , impurity , porosity , metallurgy , sintering , carbide , ceramic , chemical engineering , composite material , chemistry , organic chemistry , composite number , engineering
Densification behavior and microstructure evolution of hot‐pressed HfB 2 were studied. When unmilled HfB 2 was hot pressed at 2200°C, the resulting ceramics contained open porosity (85.8%ρ th. ). In contrast, attrition‐milled HfB 2 containing ∼0.7 wt% WC–Co milling contamination could be hot pressed to >98% density at temperatures as low as 1900°C. The addition of either boron carbide (4 wt%) or carbon (2 wt%) improved densification and reduced the temperature necessary to reach full density to 1750° and 1850°C, respectively. Full density (>99%) was achieved for additive free, attrition‐milled HfB 2 at temperatures of 1950°C or higher. Fully dense HfB 2 was also produced with the addition of 1 wt% carbon, although 2.1 vol% residual carbon remained in the microstructures after densification. The combination of carbon additions and WC impurities, introduced during milling, resulted in the formation of (Hf,W)C 0.98 solid solution inclusions. (Hf,W)C 0.98 formation suggested that carbon reacted with HfO 2 impurities, which were present on particle surfaces from powder processing. The improved densification behavior with the addition of boron carbide or carbon suggests that both additives increase hafnium and/or boron mobility.