Oxidation behavior of Mo≤5Si3C≤1 and its composites

The oxidation behavior of Moless than or equal to 5Si3Cless than or equal to 1 and its composites was studied in air over the temperature range of 500 degrees C-1600 degrees C. Experiments revealed poor oxidation resistance of monolithic Moless than or equal to 5Si3Cless than or equal to 1 at high temperature. The oxidation was quite rapid at 1200 degrees C and above, resulting in complete oxidation of specimens in a short time. The addition of 2.0 wt% boron was found to produce a Moless than or equal to 5Si3Cless than or equal to 1 composite with three other phases of MoB, MoSi2, and SiC, and showed remarkable improvement in oxidation resistance. The mechanism for the improvement was attributed to the viscous sintering of the scale to close the pores formed during the initial oxidation period. Oxidation tests were also conducted on SiC-Moless than or equal to 5Si3Cless than or equal to 1 composite at 800 degrees C, 1300 degrees C and 1600 degrees C for more than 100 hours. The oxidation resistance of the composite was found to be very good. The results demonstrate that, though oxidation resistance of monolithic Moless than or equal to 5Si3Cless than or equal to 1 is far insufficient for high-temperature applications, boron-modification and/or composites with SiC are viable methods to improve oxidation resistance to a practically acceptable level. (C) 2000 Kluwer Academic Publishers.