Processing, microstructure and properties of C40 Mo(Si,Al)2/Al2O3 composites

The C40 Mo(Si0.75Al0.25)2/Al2O3 composites were prepared by spark plasma sintering (SPS) of mechanically alloyed (MA) powders. The Mo(Si0.75Al0.25)2/0–20 vol.% Al2O3 materials, showing micron and submicron composite structure, possess a hardness of 13.9–14.6 GPa but a poor toughness of 1.78–1.80 MPa m1/2. The addition of 30 vol.% Al2O3 leads to the formation of the micron C40 Mo(Si0.75Al0.25)2/Al2O3 composite with an intergranular distribution of Al2O3, that results in a drop of the hardness to 10.2 GPa and an improvement of the toughness to 3.67 MPa m1/2. The transition of the cleavage facets to the intergranular fracture with the addition of Al2O3 is assumed as the main toughening mechanism.