Replacement materials for the superalloys currently used in gas turbine engines are needed if the operating temperature-and thus efficiency-is to be increased. Candidates include ceramics (which have problems with low Fracture toughness) and intermetallics. The materials discussed here consist of a Mo5Si3 matrix combined with one or two other phases to increase the ductility and oxidation resistance. The oxidation behavior and creep behavior are examined, in particular upon the addition of boron.