Densification Behavior and Thermal Properties of Hafnium Diboride with the Addition of Boron Carbides

• Published in: Journal of the American Ceramic Society Vol. 95; no. 6; pp. 2035 - 2043
• Main Authors: Brown-Shaklee, Harlan J., Fahrenholtz, William G., Hilmas, Greg E.
• Format: Journal Article
• Language: English
• Published: Columbus Blackwell Publishing Ltd 01.06.2012; Wiley Subscription Services, Inc
• Subjects: Boron carbide; Ceramics; Densification; Density; Heat conductivity; Heat transfer; Sintering; Sintering (powder metallurgy); Stoichiometry; Thermal conductivity
• ISSN: 0002-7820; 1551-2916
• DOI: 10.1111/j.1551-2916.2012.05208.x

Densification behavior and thermal properties of hot‐pressed HfB2–BxC particulate composites were studied. Boron carbide powders were synthesized throughout the homogeneity range (B4.3C–B˜10C) and beyond the carbon‐saturated (B3C) and boron‐saturated (B12C) limits for use as sintering additives in HfB2. Changes in the densification behavior of HfB2 were observed with changes in the B/C ratio of the boron carbide sintering additive. The most effective sintering additives were either the carbon or boron saturated boron carbides which produced composites with the highest relative densities. The improved densification behavior was caused by a combination of removal of surface oxides due to chemical reactivity and changes in the B‐ or Hf‐vacancy concentration in the HfB2 matrix phase. Thermal conductivities of the ceramics were only affected slightly by boron carbide stoichiometry. Thermal conductivities of HfB2 with 10 mol% additions of boron carbides ranged from 114 to 131 W·(m·K)−1 at room temperature and from 87 to 93 W·(m·K)−1 at 1000°C. Measureable changes in composite thermal conductivity with composition were attributed to slight differences in hot‐pressed densities that resulted from different boron carbide B/C stoichiometries.