Principal Investigator

The objective of this research was to identify the phases formed and determine some mechanical properties of reactively sintered MoSi2 and MoSi2 composites with carbon additions. The carbon additions were added via polymeric coatings on MoSi2 particles. The purpose of adding carbon was to form silicon carbide particles (SiCp) in situ and reduce the inherent presence of SiÜ2 in MoSi2. Carbon was added by two processes followed by pressureless sintering. The idea was to obtain a more uniform distribution of carbon by coating the MoSi2 particles than by simply mixing carbon powder with MoSi2 powder. The in situ formation of SiCp would increase the low temperature toughness of MoSi2 by using it as a reinforcement and also reduce the high temperature creep by reducing grain boundary sliding caused by viscous flow of SiC>2 at elevated temperatures. The carbon coating of the Mo Si2 powder was obtained by: /»henolic resin based carbon by.solvent evaporation (PRBCSE) and aqueous cfispersion_/locculation (ADF). The sintering temperatures and times ranged from 1600 to 1800 °C and 1 to 100 h, respectively. The addition of carbon did reduce the presence of SiC>2 and there was formation of SiCp. However, the SiCp formation was less than expected and, therefore, did not increase toughness significantly. The Nowotny phase (Mo<4.gSi3C<o.6) was also found in less than expected amounts. Fracture toughness did not increase appreciably in the composite samples because a maximum of 1.4 vol % SiCp was formed. But observation of crack/SiCp interaction showed promise in that if a sufficient amount of SiCp could be formed, an appreciable increase in toughness could result