Synthesis and mechanical properties of Mo≤5Si3C≤1 and Mo≤5Si3C≤1-based composites

The Moless than or equal to 5Si3Cless than or equal to 1 phase was synthesized by the reactive hot-pressing (RHP) from elemental molybdenum, silicon, and carbon powders at 30 MPa and 1500 degrees C for 1-2 h. The products were characterized using chemical and X-ray fluorescence analyses, X-ray diffraction and scanning electron microscopy. Although a small amount of SiO2-rich glassy phase (about 1 wt%) is contained, compacts consisting of only the crystalline Moless than or equal to 5Si3Cless than or equal to 1 phase can be produced from Mo, Si and C powders via a hot-press sintering process. Phase relations in the Mo-Si-C system and lattice parameters of the Moless than or equal to 5Si3Cless than or equal to 1 phase were examined. Fracture strength, Vickers hardness and fracture toughness of Moless than or equal to 5Si3Cless than or equal to 1 hot-pressed at 1500 degrees C for 2 h were 485 MPa, 12.1 GPa and 3.3 MPa.m(1/2), respectively. These results suggest the potential of Moless than or equal to 5Si3Cless than or equal to 1 not only as a new reinforcement second phase but also as a new matrix material of composites of Mo-Si compounds. Moless than or equal to 5Si3Cless than or equal to 1/Mo2C and Moless than or equal to 5Si3Cless than or equal to 1/MoSi2 in-situ composites were also prepared by controlling Si content. The surface of Moless than or equal to 5Si3Cless than or equal to 1/Mo2C composite was easily corroded particularly in the presence of moisture. On the other hand, Moless than or equal to 5Si3Cless than or equal to 1/MoSi2 composite showed better corrosion resistance, and well-balanced mechanical properties. The Moless than or equal to 5Si3Cless than or equal to 1-MoSi2 pseudo-binary system may be of importance for new high-temperature structural materials. (C) 1997 Elsevier Science Limited. All rights reserved.