Self-healing ability of Nb-Si based alloys with boron for improved environmental performance

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Materials in turbine engines are exposed to harsh in-service environments, resulting in the reduction in their integrity and performance. To improve efficiency of engines and to decrease emissions of NOx/CO2, turbine engine temperatures will be increased. Current turbine blade materials are approaching melting temperatures; hence new refractory materials are needed.Nb-Si based alloys are currently investigated to replace Ni-based superalloys used in the hottest part of a turbine engine. Although these materials have good mechanical properties, the oxidation resistance can be poor, which limits their application. Improving the oxidation resistance is the challenge to be addressed in this project.The issue is to be tackled utilising the unique nature of boron. Boron is one of the glass-forming elements. When added to Nb-Si alloys, a glassy self-healing layer may form on the surface upon oxidation of the alloy, improving oxidation resistance. The project investigates the effect of introducing boron on the properties of Nb-Si based alloys through materials characterisation and isothermal and cyclical oxidation tests. The project aims to determine the oxidation mechanism, the impacts of boron introduction and its synergy with commonly used additions e.g. Al, Sn, Ge etc. The experimental outcomes will be compared with computational models. This work will lead to the discovery of alloys with improved oxidation resistance and self-healing ability, which could save significant in-service costs. Once established, this knowledge may be extended to other alloy systems.