HfB2 ceramic polycrystals: A low-temperature metal-like ceramic at high temperatures?

Hafnium diboride (HfB2) is a highly refractory (melting above 3000°C) ceramic with many potential applications at high temperatures. To enable its use at temperature for extended periods its high-temperature plasticity must be known. This paper examines the mechanical response at temperatures between 900°C and 2000°C in air and in a reducing atmosphere, interpreting the data in the frame of classical models for the plasticity of compact-packed metals at low temperatures. In particular, the Friedel law and the principle of similitude for dislocation patterning are assessed. This reveals that HfB2 is a singular example of a ceramic material with “metal” mechanical behaviour.