Synthesis and characterization of dense ultra-high temperature thermal protection materials produced by field activation through spark plasma sintering (SPS): I. Hafnium Diboride

The consolidation of HfB2 by sintering and reactive sintering using the field-activated process of the spark plasma sintering (SPS) method was investigated. Sintering of the diboride at 1900◦C under a pressure of 95 MPa did not result in dense materials. In contrast, reactive sintering at 1700◦C produced about 98% dense HfB2 with a 10 min hold at temperature. In contrast to previous observations, the reaction between the elements and the consolidation of the resulting diboride did not coincide, the latter occurring at a much higher temperature. The reaction mechanism between B and Hf during reactive sintering was investigated. Measured rates of growth of the HfB2 were found to be in agreement with calculated values from diffusion couple experiments, suggesting that the current did not play a significant role in the reactivity. C 2006 Springer Science + Business Media, Inc.