Effects of WC contamination on the densification of spark plasma sintered monolithic HfB2

Abstract

Monolithic HfB2 samples were produced by SPS at 1800 °C and 2050 °C with two heating rates of 77 °C/min and 107 °C/min, respectively. Despite the increase in the heating rate, relative densities variations against the densification time didn't show any significant change. The apparent activation energy and its changes during the densification were calculated using the master sintering curve. An abrupt increase from 20 to 50 kJ/mol to 250 kJ/mol indicated the activation of a sinter mechanism with high activation energy at high temperatures (above 1600 °C). The measured relative densities above 95% for both samples favored this change in the densification mechanism. Microstructural assessments revealed a tungsten-rich liquid-like phase most probably introduced into the primary powder during the high-energy ball mill. Also, the formation of W solid-solution in HfB2 was shown using EDS analysis and underpinned by peak shift in XRD patterns.