Mechanical properties of HfB2 whiskers

Nanoindentation has been used to study mechanical behavior of HfB2 whiskers 10–20μm in diameter in a directionally reinforced ceramics. For comparison a bulk (0001) HfB2 single crystal 5 mm in diameter has been tested. For both the samples a pop-in due to the nucleation of dislocations in a previously dislocation-free region under the indent has been observed. It has been shown that for a HfB2 whisker in reinforced ceramics the critical load of the elastoplastic transition is twice as high as for a bulk HfB2 single crystal and, the maximum shear stress, at which the nucleation of the first dislocation loop in a HfB2 whisker occurs, approaches to the theoretical shear strength value. The observed effect has been caused by the higher structural perfection of whiskers as compared with a bulk sample. Hardness and elastic modulus of the HfB2 whisker are higher than that of the bulk crystal by 10 and 3%, respectively.