Improved ductility and oxidation resistance in Nb and Al co-substituted MoSi2

Polycrystalline samples of (Mo1−xNbx)(Si1−yAly)2 with x = 0.0–0.03 and y = 0.0, 0.04 were prepared by arc melting followed by densification by hot pressing. The mechanical and oxidation behaviors of high density polycrystalline pellets were evaluated. Thermogravimetric analysis shows lower oxidation in (Mo1−xNbx)(Si0.96Al0.04)2 samples compared to pure MoSi2. X-ray diffraction analysis of the oxide scale revealed the presence of α-Al2O3 peaks. Mechanical characterizations carried out on (Mo0.99Nb0.01)(Si0.96Al0.04)2 composition show a marked improvement compared to that of unsubstituted MoSi2. Micro-hardness measurements reveal a lowering of the room temperature hardness and stiffness compared to pure MoSi2. Plastic deformation under compression is observed at room temperature with a yield stress of 500 MPa. The K1C value increased from 3.33 (±3) MPa m0.5 to 4.05 (±0.3) MPa m0.5 with the fracture mode being predominantly transgranular.