Ternary Alloying of Refractory Intermetallics

Abstract

ABSTRACTOne of the most attractive attributes of intermetallics is their potential for alloying to achieve the desired balance of engineering properties via the creative use of in-situ composite processing. Following our initial investigation of 20 binary refractory intermetallics, selected primarily on the basis of structure type; seven systems were down selected for ternary alloying, based on a balanced consideration of room temperature toughness, high temperature creep strength, oxidation resistance and ultimate strength. These systems were Nb3Al and Cr3Si with A15 structure, CO2Nb and Cr2Nb Laves phases with C14/C15 structure, MoSi2 with C11b structure, and Nb2Al and Mo5Si3 sigma phases.The alloying potential of each of these binary systems is evaluated with respect to solubility limits, phase relationships, melting point suppression with alloying, and potential for enhancement of creep resistance. The results show that, with alloyed intermetallics, realistic creep strength is attainable and several opportunities exist for in-situ processing of intermetallic based composite systems to improve room temperature toughness.