Mechanical properties of superconducting MgB2 materials are important for their practical uses. This paper reports relationships between mechanical properties (Vickers hardness and fracture toughness) and the microstructure in MgB2 bulk materials. MgB2 bulk specimens were prepared by a Premix-PICT (powder in closed tube)-diffusion method. It was found that Vickers hardness and fracture toughness were improved up to about 1.5 times by co-doping with SiC and C10H8. It is interpreted that (i) the improvement of Vickers hardness by the co-doping is mainly due to reducing the MgB2 grain size, and (ii) the improvement of fracture toughness by the co-doping is mainly due to decreasing the amount of amorphous phases.
