Beyond Nickel Based Superalloys

Abstract In the most advanced gas turbine engines, the gas temperature exceeds the melting temperature of Ni based superalloys. Further improvements in the performance of gas turbines require operation of metallic materials at higher temperatures. Research programs on Nb and Mo silicide based alloys have demonstrated that these materials can offer attractive mechanical properties that justify their consideration as suitable candidate materials to replace Ni based superalloys in specific structural applications in gas turbine engines. The research has also demonstrated that oxidation behavior of developmental alloys can be significantly improved via selection of specific alloy elements. The ongoing research to develop new alloys is outlined with the emphasis on new metallic materials based on the refractory metals Nb and Mo. For the Nb based alloys, alloy development research based on the Nb–Si–Ti system with transition/refractory and free electron metal additions is reviewed. For the Mo based alloys, the review concentrates on alloys based on the Mo–Si–B and Mo–Si–Al systems.