Hardness and toughness of MoSi2 and MoSi2–SiC composite prepared by reactive sintering of powders

Samples of monolithic MoSi2 and a MoSi2–SiC composite have been prepared by milling elemental powders followed by reactive hot pressing to dense materials with fine microstructures. Mechanical properties (hardness and toughness) have been deduced from hardness imprints and related to the scale of the microstructure. Toughness is increased somewhat in the monolithic intermetallic at fine grain size as well as by the addition of the SiC second phase. Cracking begins always by intergranular decohesion, which seems little affected by the grain size or the presence of the second phase, and subsequently becomes transgranular in MoSi2 and mixed transgranular–intergranular in the MoSi2–SiC composite. The propagation of such longer cracks depends on the microstructure, with both finer matrix grain size and the presence of SiC leading to more difficult crack growth.