SYNTHESIS AND MECHANICAL-PROPERTIES OF ESS-THAN-OR-EQUAL-TO-5SI3C-LESS-THAN-OR-EQUAL-TO-1 AND AN-OR-EQUAL-TO-5SI3C-LESS-THAN-OR-EQUAL-TO-1-BASED COMPOSITES

The Moless than or equal to 5Si3Cless than or equal to 1 phase was syn thesized by the reactive hot-pressing (RHP) from elemental molybdenum, silicon, and carbon powders at 30 MPa and 1500 degrees C for 1-2 h. T he products were characterized using chemical and X-ray fluorescence a nalyses, X-ray diffraction and scanning electron microscopy. Although a small amount of SiO2-rich glassy phase (about 1 wt%) is contained, c ompacts consisting of only the crystalline Moless than or equal to 5Si 3Cless than or equal to 1 phase can be produced from Mo, Si and C powd ers 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 ha rdness and fracture toughness of Moless than or equal to 5Si3Cless tha n 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 pot ential of Moless than or equal to 5Si3Cless than or equal to 1 not onl y as a new reinforcement second phase but also as a new matrix materia l 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 e qual to 1/Mo2C composite was easily corroded particularly in the prese nce 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 impo rtance for new high-temperature structural materials. (C) 1997 Elsevie r Science Limited. All rights reserved.