Pressureless sintering mechanisms and mechanical properties of hafnium diboride ceramics with pre-sintering heat treatment

A pressureless sintering process with two pre-sintering heat treatments was developed for the densification of HfB2. The use of two isothermal holdings, at 1650 and 2000 °C, prior to the final sintering temperature (2200 °C) proved to be more effective at removing oxygen impurities and rearranging the initial powder compact microstructure. The mechanical properties of HfB2 with 2 wt.%B4C, including hardness (19.5 GPa), E modulus (529 GPa) and strength (469 MPa), were comparable to hot-pressed samples or higher than the values using other sintering aids.