Role of Zr in strengthening MoSi2 from density functional theory calculations

MoSi2 is an important intermetallic with excellent oxidation resistance at high temperatures above 1000 degrees C. However, its application at lower temperatures is limited by oxygen embrittlement, a phenomenon known as pesting. In this work, we comprehensively investigate the role of Zr in mitigating pesting in MoSi2 using density functional theory calculations. We show that Zr dopants reduce the embrittling effects of oxygen interstitials at MoSi2 grain boundaries by being a charge donor to oxygen. However, a more substantial effect is observed when Zr is present as a secondary getter nanoparticle phase. Oxygen interstitials have a strong thermodynamic driving force to migrate into the Zr subsurface at the Zr/MoSi2 interface, and the work of separation of the clean and oxygen-contaminated Zr/MoSi2 interfaces are much higher than that of MoSi2 grain boundaries. Finally, we present an efficient screening approach to identify other potential getter elements using simple thermodynamic descriptors, which can be extended to other alloy systems of interest. These findings provide crucial fundamental insights and further avenues to optimize Mo and other alloys. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.